Understanding the regulation of double barrel rifles

IvW

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I am having a hard time understanding exactly how this is supposed to be.

Some manufacturers will stipulate regulation at 50m or yards others(often German)70 meters or yards and then others with smaller calibers will stipulate regulation at 100....so what exactly does this mean? Does it mean that both barrels hit the same spot at the given distance and then start drifting further apart? So they start out barrel distance apart cross at 50 and ten they are barrel distance apart at 100 again and from there on further and further apart?
Some folks say a properly regulated double will be regulated with the two bullets striking barrel center distance apart irrespective of the distance, if this was the case then crossing with the regulated load should not happen with a SxS.

According to Westley Richards regulation is: Regulating the barrels of a rifle means adjusting/regulating the 2 barrels of a rifle to shoot to the same point of aim at a given distance. This is achieved by a repetitive process of shooting the rifle and then making minute adjustments to individual barrels in a specific jig, ultimately moving the barrels to the correct the point of impact.

Another source quotes: Acceptable results equate to an inch and a half at 65 yards. Some people prefer a longer distance these days, especially boar hunters, who often want the rifle regulated to one hundred yards. The regulation distance is important. For example, a rifle regulated to touch bullets at fifty yards will be crossing at seventy; meaning the right barrel’s bullet will impact to the left of the left barrel’s bullet. Barrels regulated to shoot within and inch and a half of each other at sixty five yards, won’t start to cross until they reach a hundred yards.

So which is correct? As this means the regulation will have the bullets cross at the given distance or am I confused?

Then O/U rifles seem to be a better option when wanting an all purpose or small to medium bore( lets say 7x57R to about 450/400 NE) double as it does not have the same regulation issues or not?
 

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Ive been reading as much as I can as I am in the search for my first double. From my research, the majority of respectable authorities on the subject have given the response that properly regulated DR's should never have a crossing bullet path. Obviously forces impact the bullet and it will lose its fight with physics and the trajectory will decay. Before that point you want the trajectory to be no more than the distance between bore center to bore center at your needed, or the manufacturer stated, regulation distance. This is not always the case so 1.5" is usually used as the guide for 50 meters, but 1"-3" is also stated to be acceptable depending on the manufacturer. Also why it is good practice to see what each barrel does 15, 25, or even 50 yards beyond the regulation distance...

As you mentioned for O/U's, my research and both handling and shooting a few DR's has moved me to wanting a O/U over a SXS. I shoot O/U exclusively for double barrel target & upland hunting so its more comfortable and natural, for me. Secondly, I have read and heard that an O/U can be inherently better for a longer range shot (75-100+ meters), should the absolute need arise. I very recently was able to shoot a 470 O/U next to a 450NE SXS and found this to be true, again, for me. I was more precise on a longer shot with the O/U even with noticeable more recoil. This can all be related to my exclusiveness to use O/U shotguns, but I am glad I had the chance to shoot a O/U and SXS at the same time. I have also heard the regulation of a O/U can be easier, though I have not spoken to enough smiths that have a bias on that specific subject.

Just my greenhorn .02, as again, I'm in the market, and trying to gather as much info and experience before the investment.
 
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I want a double not to cross and to be the distance of the muzzles apart at 65 yards ( think that's dinstance used by English makers...what I know Paul used ) continuing out to 100 yards...which my 9.3 used to do....a lot especially the bigger Cals will be slightly up or down from each barrel at 65 or so.....presume that's because they think that the rifle is going to be used at or around that distance. ...also complicated regulating a double
 

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Explaining "barrels regulation"...

Let me give it a shot (pun fully intended) :)

The two barrels should shoot together, right? Whether "together" means shots touching, 1" apart, 2" apart, etc. can be discussed endlessly, but it seems that for DG hunting out to 50 meters/yards with iron sights, 2" groups are OK.

On DG doubles built for .500 case-head (that includes most .400, .450, .465, .470, .475, .476, .500), the two barrels are about 1" apart, bore center to bore center, at the breech, so one would think that if they stayed parallel, 1" apart, bore center to bore center, all the way to the muzzle, the two barrels would shoot parallel into eternity, right?

That is almost, but not quite 100% true with the over/under rifles because both barrels recoil in the same vertical axis as the rifle stock grip, and almost the same vertical axis as the stock (depending on stock cast). Therefore, recoil is essentially in straight line and there is no sideways yaw. This is why O/U doubles rifles are easier and cheaper to make, and much less sensitive to ammo variations (bullet weight, bullet bearing surface, velocity, etc.), and when changing ammo with them, most of the changes are addressed with replacing the front sight to move the point of impact (POI) higher or lower to the point of aim (POA).

Where the side by side doubles are different, and the bigger the caliber, the more pronounced the difference, is that neither barrel is in the same vertical axis as the stock grip and stock. The left barrel is left of the stock, and the right barrel is right of the stock. What this means is that the left barrel pulls the rifle left under recoil, and the right barrel pulls the rifle right under recoil. This is the "yaw." The two shots diverge under recoil. Always. How much to the left and to the right? It depends how long the bullets take to go through the barrels (bearing surfaces, velocity, barrels length, etc.), hence how long the recoil lasts, and how much recoil and yaw there is (caliber, bullet weight, velocity, powder charge, etc.).

The only way to get the two shots "together" is for the two barrels to mechanically converge when assembled. The typical .470 will have about 1" distance bore center to bore center at the breach, and about 0.75" distance bore center to bore center at the muzzle. The barrels clearly converge. This is an easy-to-verify fact.

The art of barrels regulation is to have the two barrels converge just enough when soldering the front wedge between them, so that the convergence of the barrels compensates exactly for the divergence of the shots under recoil. In a perfect world, the barrels convergence at the muzzle would be just so, and the rifle would shoot two parallel trajectories and the two shots would never cross nor spread.

This would be the ideal world, but this is not the real world, if only due to the fact that no two shooters get the same group from the same rifle, because no two shooters control recoil exactly the same way and keep the rifle from yawing left then right exactly the same way.

In the real world, the process of barrels regulation means soldering the front wedge between the barrels/shooting/unsoldering and moving the wedge/resoldering the wedge;
... and again shooting/unsoldering and moving the wedge/resoldering the wedge;
... and again shooting/unsoldering and moving the wedge/resoldering the wedge;
... and again, and again, etc. until the result is deemed good enough.
Good enough is not the same for each gunmaker. Good enough is when the gunmaker meets his goal (whichever that goal might be) and calls it quit. The less expensive the double, the faster this time comes. Push time savings - understand: costs savings - to its limit, and some makers try to replace the "solder/shoot/unsolder" process with blind soldering of a CNC machined wedge, and there is no predicting what group size the rifle will shoot, and where it will shoot it. Enter the infamous Dremel to start altering the crowns and push bullets right or left as they leave the barrels...

The really good regulators get the barrels close to shooting parallel, but very rarely do they shoot perfectly parallel, so all doubles will tend to cross (at 50 meter/yard? 75? etc.) or they will tend to spread (1" group at 25 meter/yard, 2" at 50? 3" at 75? etc.). This is just the nature of the beast. And that is the day the rifle was regulated, with the ammo lot used, and with the shooter used... Then the sights are adjusted so that the point of impact (POI) covers the point of aim (POA).

Now, add to that, even when shooting the exact same bullet with which the rifle was regulated, some differences in powder lots, temperature of the place (Africa vs England or Germany), barometric pressure (altitude), humidity, shooter form, shooter's ability to control recoil and yaw, shooter fighting the recoil or rolling with the recoil, etc. and most doubles fired by most shooters will not shoot parallel and their shots will either converge or diverge.

In the old days, the British gunmakers regulated their doubles to cross at 50 to 65 yards in England because cordite developed higher pressure in warm Africa than in cold England, so when the rifles were shot in Africa, the higher pressure caused more recoil. More recoil caused more yaw and divergence when shooting, and the crossing at 50 to 65 yards either moved to 100 yards, or maybe was replaced by spreading at 100 yd, which was fine enough for any real world application.

In the old days too, the British gunmakers also insisted that the rifle be shot during regulation by the client himself, so that the clients's unique way of controlling recoil and yaw would be built into the regulation. When they built for clients with considerable experience (e.g. professional ivory hunters) they built a little less convergence into the regulation because these guys knew how to control recoil and yaw. Conversely, rifles for first time safari clients usually had a tad more convergence, because it was likely that the rifles would yaw a little more under recoil.

So, in summary, there is no hard rule for what is regulation of double rifles, because the results will change with the same rifle shooting differently for different shooters, even with the same load. Never mind with different loads. In the real world, a rifle is very well regulated in my view when it keeps 2 shots from each barrel of its regulation load in a 2" group anywhere between the muzzle and 50 yards. And, realistically, 3" is OK too in my view. Whether this group at 50 yd has the two left shots on the left of the group (no crossing - preferable) or on the right of the group (crossing likely around 40 yd and starting to spread at 50 yd - less desirable), is essentially OK too as long as one does not try to group this rifle at 100 yd. And this will change when the shooter changes bullet shape, load, powder lot...

Developing the loads a fraction of a grain at a time to increase or decrease the amount of yaw (recoil energy) and the time the bullet spend in the barrel (velocity) will increase or decrease the divergence of the shots between recoil, and will bring the rifle into the convergence built into the way the wedge was soldered.

Sorry, this is again probably too long of a post, but this is not an easy subject to compress into just a few sentences...

I hope this answered the questions :)
 
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Ridgewalker

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Yes Pascal, I took a nap in the middle...just kidding! Yes that makes since. A 2” group at 75 yards (or what ever one decides is their normal DG range) with the left barrel left of center and the right barrel right of center would be excellent IMO! Minute of any DG.
 

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One Day,
Very well said. I've wondered about regulation for some time and could not make much sense of what I read. Too many differing theories. Now Ihave a much clearer picture. Thanx.
 

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Ive been reading as much as I can as I am in the search for my first double. From my research, the majority of respectable authorities on the subject have given the response that properly regulated DR's should never have a crossing bullet path. Obviously forces impact the bullet and it will lose its fight with physics and the trajectory will decay. Before that point you want the trajectory to be no more than the distance between bore center to bore center at your needed, or the manufacturer stated, regulation distance. This is not always the case so 1.5" is usually used as the guide for 50 meters, but 1"-3" is also stated to be acceptable depending on the manufacturer. Also why it is good practice to see what each barrel does 15, 25, or even 50 yards beyond the regulation distance...

As you mentioned for O/U's, my research and both handling and shooting a few DR's has moved me to wanting a O/U over a SXS. I shoot O/U exclusively for double barrel target & upland hunting so its more comfortable and natural, for me. Secondly, I have read and heard that an O/U can be inherently better for a longer range shot (75-100+ meters), should the absolute need arise. I very recently was able to shoot a 470 O/U next to a 450NE SXS and found this to be true, again, for me. I was more precise on a longer shot with the O/U even with noticeable more recoil. This can all be related to my exclusiveness to use O/U shotguns, but I am glad I had the chance to shoot a O/U and SXS at the same time. I have also heard the regulation of a O/U can be easier, though I have not spoken to enough smiths that have a bias on that specific subject.

Just my greenhorn .02, as again, I'm in the market, and trying to gather as much info and experience before the investment.

But this contradicts the way all the major double manufacturers regulate there rifles.
 

IvW

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I want a double not to cross and to be the distance of the muzzles apart at 65 yards ( think that's dinstance used by English makers...what I know Paul used ) continuing out to 100 yards...which my 9.3 used to do....a lot especially the bigger Cals will be slightly up or down from each barrel at 65 or so.....presume that's because they think that the rifle is going to be used at or around that distance. ...also complicated regulating a double

I agree. If let's call it "Parallel" regulation is achieved then the two barrels will shoot side by side all the way until the bullets hit the ground or not?
 

IvW

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It appears that the top double manufacturers regulate for the barrels to cross. 65 yards seems to be the standard for British regulation, reason given is that in the warmer climate the pressure will go up resulting in the barrels crossing sooner at about 50 meters.

Posted on May 21, 2014 by Simon Clode
REGULATING A DOUBLE RIFLE AT WESTLEY RICHARDS




The process of regulating a double rifle is one that we are doing on a very regular basis here at Westley Richards. With over 45 double rifles currently on order in the factory, it equates to nearly one rifle a week. The task of regulating the rifles falls in the safe hands of Stuart Richards who was himself taught the process by both Keith Thomas and Ken Halbert. Both were past foremen in the factory who undertook our regulating during their time here.

Regulating the barrels of a rifle means adjusting/regulating the 2 barrels of a rifle to shoot to the same point of aim at a given distance. This is acheived by a repetitive process of shooting the rifle and then making minute adjustments to individual barrels in a specific jig, ultimately moving the barrels to the correct the point of impact.

At Westley’s we shoot our rifles on our range, this is equipped with both a chronograph and an electronic target system. The chronograph measures the individual velocity of each shot, a consistent velocity is required to judge the shots and this way we are able to pick up any ‘flyers’ meaning low or high velocity shots and these can then be discounted in any adjustments. I would emphasise, that without very consistent loads, regulation is impossible, and this is an area we have invested a considerable amount of time and money on here over the years. The electronic target system provides an accurate history of all the shots taken during the regulation process.



Having shot the rifle with 4 shots to confirm accuracy the rifle is then disassembled, front sight removed and the barrels are placed in a regulating jig as seen above. This jig supports the barrels and allows individual adjustments through the use of 9 hex head bolts. There is a wedge in the muzzle of the rifle which aides in the barrels being drawn either inwards (draw wedge out) and apart (push wedge in).

Having set the barrels firmly in the jig, the muzzle ends are heated up to a point where the solder holding the barrels together begins to melt, at this point the barrels can be independently moved in any direction to obtain the correct convergence and point of aim. This is done by relieving the opposing bolt and tightening the other side. Adjustments are made in small movements of about .0010″ a time although this is where the process becomes one of feel and knowledge rather than pure measurement. The barrels are then allowed to cool down completely after which they are cleaned and the process begins again and is repeated until the desired result is achieved.

Flux is applied to the barrels to keep the solder running freely during heating.



Drawing out the wedge in order to move the barrels closer together.

Minute adjustments are made in the jig using hex key.

The barrels cooling down in jig. The wire wraps are in place to keep the barrels in place.







A series of 4 targets showing the movement of the shots after regulating in jig.

Stuart Richards with another completed rifle.

I can say without hesitation that in all my years here with the company, the regualtion process has not been done as efficiently and accurately as it is being done now in the careful, young and enthusiastic hands of Stuart Richards who tells me his fastest regulation was in 8 shots and the longest over 100 shots, and also points out that the large calibre’s are so much easier than the small ones. I know there is a sincere sense of pride every time he produces a final target which are always exceptional.

This entry was posted in Gun Making, New Guns, People by Simon Clode.

Is it science? Is it magic? Is it a formula or a dark art? Everyone seems to have an opinion about the best means of getting a rifle with one barrel attached to another to place two shots side-by-side within an inch or two of one another, at the desired range. Diggory Hadoke gets to grips with the gritty subject of double rifle regulation.

Not many companies still make double rifles. In the UK, I can name a handful: Holland & Holland, Rigby, Purdey, David McKay Brown, Westley Richards. Of continental makers, Chapuis, Heym, Krieghoff spring to mind. The double rifle, once the mainstay of the deer stalker, the big game hunter and the driven boar enthusiast, has largely been surpassed by bolt-action magazine rifles, which are cheaper to make, accurate, reliable and, above all, easier to make shoot tight groups and simple to adjust, as and when necessary; for example, when changing optics or ammunition.

The old double rifles of the Victorian and Edwardian eras were painstakingly tested and adjusted in order to make them deliver accurately, with the desired powder load and bullet weight. Looking into the cases of vintage double rifles, we will often see, on hand-written labels, pasted to the lid, detailed loading instructions, with specific notes on powder, bullets, wads and patches. If the sportsman followed the recipe, he could be confident that the rifle would shoot in the manner intended. The necessary bespoke loading tools were often included in the case.

I met up with one of Britain’s foremost rifle regulators, Keith Dennison Thomas, while he was busy regulating a new .416 Rigby double ‘rising bite’ side-lock at the West London Shooting School. Not to be confused with Keith Thomas, the gun engraver, Keith has over two decades of regulating double rifles under his belt. He explained to me some of the procedures and challenges of making double rifles shoot accurately.

The tools of the trade.

Regulation takes place at the range. There are indoor ranges, like to one at Westley Richards, which is fully enclosed underground. There are also open air ranges, like the one at the West London Shooting School.

Arriving at the range, the regulator will have with him a collection of essential kit to be employed during the process. The most obvious being ammunition. This needs to be from a single batch, to minimise variation. The average rifle requires sixty rounds of ammunition to regulate.

The regulating jig is a contraption that fits over the barrels and has hex head bolts in multiple positions for adjustment. A gas bottle is required to provide the heat, binding wire and aluminium wedges are for support. Measuring tools, pliers, rosin flux, tin wire, a lighter, cleaning brush and a tin to store the front sight when not in place complete teh essentials.

If a proper bench and vice is available, as at Westley Richards, that is ideal. If not, a Black & Decker ‘Workmate’ will do the job. British weather being what it is, if working outdoors, a shelter of some kind is helpful.

The job is made easier if two people are involved. If one shoots and one spots (good optics make this faster), it saves time. Also, the strain of repeatedly firing a heavy rifle is better spread between two over the day. Recoil fatigue can affect the shooter and the results.

For a target, the initial four sighter shots are fired at a black dot. This initial shot sequence provided a datum point for the rest of the work. Thereafter, the A3 size half-moon target is used, with a one inch grid pattern to make adjustments easier to calculate from up range. For example, a British .470 will approximate a thou’ of adjustment at the muzzle with an inch of movement on the target at 65 yards.

Regulating new rifles.

Once set up at the range, those first shots will determine the next move. Most new rifles will arrive with a consistent point of impact, usually within six to eight inches of each other. Keeping the sight in the centre, one barrel is moved at a time. To adjust the right barrel, the left is clamped and the barrels heated with the torch to melt the tin. The barrels will expand five to seven thou’ when hot. The wedge is moved and pressure applied to the right barrel in the jig. It moves, is allowed to cool, then test fired again. The process is repeated until the regulator is happy with the result.

Acceptable results equate to an inch and a half at 65 yards. Some people prefer a longer distance these days, especially boar hunters, who often want the rifle regulated to one hundred yards. The regulation distance is important. For example, a rifle regulated to touch bullets at fifty yards will be crossing at seventy; meaning the right barrel’s bullet will impact to the left of the left barrel’s bullet. Barrels regulated, as Keith prefers, to shoot within and inch and a half of each other at sixty five yards, won’t start to cross until they reach a hundred yards.

A number of factors affect the results of each part of the regulating process. Light, thin rifle barrels on many foreign double rifles react more erratically to each adjustment than the, traditionally thick, barrels on British rifles. Small calibres are very sensitive and often the act of heating alone will cause the point of impact to change significantly. This is where the regulator must draw on his years of experience to ‘feel’ each adjustment as he eases the barrels to the optimal positions for performance. In general, big, slow bullets are easier to regulate than small fast ones.

Regulating old rifles

Many a hunter has eyed the tempting array of fine double rifles in the auction racks and mused about taking one to Africa. It is something of a lottery to get involved in this game. I was with a client at Holt’s a few years ago and we picked up a lovely George Gibbs boxlock double rifle in .22 Savage Hi-power. Fortunately, the targets supplied with the rifle to show its performance were accurate and I later hunted wild turkey in Texas with it.

However, the same client had a .375 flanged by Cogswell & Harrison, which a US based regulator failed to get to shoot acceptable groups before a trip to hunt dangerous game in Africa. That rifle eventually found its way to Westley Richards for regulating. It now shoots very well and I killed a huge crocodile with it in Tanzania a few years later.

Ammunition

Whatever its origins, when a rifle was made, it would have been carefully regulated with the desired ammunition, with a particular weight and grain of black powder or one of the emerging ‘smokeless powders’ of the early twentieth century, such as Cordite. To replicate the performance characteristics of these powders today requires some experimentation.

Kynamco have, for some years produced ‘obsolete’ calibre ammunition for sportsmen but a lot of people load their own ammunition, with the help of technically useful books, like ‘Shooting the British Double Rifle’ by Graeme Wright, and careful experimentation at the range. This way, some of the once dormant rifles of the past, like the beautiful black powder express hammer rifles of the 1870s and 1880s in .450 and .500 calibre have been brought back into service. Also, some of the big double nitro express rifles for dangerous game. like the .450 N.E, which fell out of favour before the First World War are now being carried in the bush and put to good use.

A key issue for double rifle performance is consistency of ammunition. Federal .470 cartridges have not changed since the 1990s and will perform exactly the same today as they did 30 years ago. Kynamco have periodically changed their brass supplier, primers and powder, totally changing the characteristics of each round. One newly regulated .375 was shooting 1 1/2” groups and when a new box of ammunition was introduced, the groups moved to 6 1/2”. That is no use for hunting! It is best to buy a large quantity of same batch ammo when you set up the rifle: enough to last your lifetime of shooting (fortunately big doubles do not normally get fired hundreds of times a year).

A word of warning; monolithic solid bullets have become the desired projectile in some quarters but Keith will have nothing to do with them. The old steel barrels do not handle them well and will be irreparably damaged by their use. ‘I won’t use any monolithic or hydrostatic bullets”, he told me, “They have destroyed a lot of good rifles”. Tell tale signs include the appearance of a shadow of the rifling on the outside of the tubes, or ripple effects in the steel.

Learning to be a regulator

Regulating rifles is not an easy job for the hobbyist to have a go at. Many have been delivered to professionals, like Keith, here, after American or Australian enthusiasts have ‘had a go’. The usual problem is that by heating the barrels, they lose all the solder that holds them solid and the rifle then ‘shoots all over the shop’, according to Keith. In such cases, the barrels need to be fully stripped and ribs re-laid. The accumulated debris under the ribs needs properly cleaning out first.

Keith learned how to regulate by helping Paul Willis and David Perkins when they were doing the job for Rigby and Paul Roberts, back in 1994. At first, Keith was there to shoot the rifles but the two masters soon involved him in the regulating and taught him the skills to undertake the whole job for himself. Keith then spent a decade working for Purdey and a period in self-employment, building guns and rifles as well as regulating rifles for several gunmakers, before taking a foreman’s position at Westley Richards in 2007. Five years ago he returned to a free-lance role and continues to work for a number of gun and rifle makers.

We are fortunate to still have a small number of really skilled and experienced professionals, like Keith Dennison Thomas, who understand, and can perform, these essential services for the bespoke gun building trade. Without them, many of our old and new rifles would never perform to their potential and deliver the service that we hunters need. I just hope he passes his skills on to the next generation.

Published by Vintage Guns Ltd on 28th June 2019
 

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sestoppelman

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We hashed this out here some time ago. Some believe that once properly regulated to have the two bullets more or less meet at a specified distance, that they will then magically go side by side into eternity. We went round and round about this. I believe and one of the masters in his book stated that this was not so. As described above; since there must be a convergence to regulate for a certain distance, once that is met, the bullets will continue on in the direction they needed to converge in the first place. Thus they will not go side by side into eternity. In reality it hardly matters except that one should test the individual rifle at various distances so they know how much the spread is beyond regulation distance. It might not amount to much, but it will be there.
 

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But this contradicts the way all the major double manufacturers regulate there rifles.

You may want to check out the Nitro Express forums as this has been debated to death. You will read examples of this debated going back to the mid-late 19th century. Some have stated that manufactures like Heym and VC will make them parallel or cross to the clients wishes. Then again, many Smith's here say parallel is the proper way to go.

My preference would absolutely be parallel. I'n an ideal world I would rather have two flight paths be 1-1.5" apart from muzzle to where the bullets hit the ground. That almost certainly wont happen but a crossing path after regulation difference just means compensating for each barrel individually should a longer distance shot be needed in a SXS. This may be the norm or proper in some channels, or many might say a DR isnt for that range. If I were to have a DR made by VC I would certainly ask for parallel and hope that they would be tight and never cross paths.
 

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I agree. If let's call it "Parallel" regulation is achieved then the two barrels will shoot side by side all the way until the bullets hit the ground or not?

Not sure as wind etc might have something to say....but my 9.3 was regulated perfectly as far as I am concerned. ..if I bought a double and it crossed inside of 100 yards it would go back. ...as I have mentioned before I shot a Rigby 470 during it being regulated...the person doing it used a black and decker workmate bench...blow torch.....wire and rods for twisting barrels to alter impact point and he looked like some old wizard ....he was increliable to watch doing his magic....Paul said he was the best at regulating a double rifle....unfortunately he passed away a couple of years after that...but was privilege to have watched an old craftsman doing his thing
 

One Day...

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It appears that the top double manufacturers regulate for the barrels to cross. 65 yards seems to be the standard for British regulation, reason given is that in the warmer climate the pressure will go up resulting in the barrels crossing sooner at about 50 meters.
Not sure if you read my explanation post above IvW, but it is the opposite.

Brits regulated doubles to cross with cordite in Britain at whatever distance (in the 50 to 75 yd bracket generally, or as specified by the client), so that when shot with cordite ammo cooked in the African sun the higher pressure would result in the barrels crossing further (not sooner), in the 75 to 100 yd bracket (higher pressure increases the yaw under recoil, hence increases the divergence of the shot.).

The hope was certainly for the higher pressure shots to not cross anymore, and not spread either, thereby achieving the mythical balance where the convergence of the barrels compensates exactly for the divergence of the shots and the two barrels actually shoot apparently parallel trajectories, byt the key operating word in this sentence is "hope" and I say "apparently parallel" because it is very unlikely that the trajectories are actually parallel.

However, as alluded to by spike.t, if the crossing or spreading only becomes visible past 100 yards, that is good enough to be called "parallel" in the real hunting world. After 100 yd, the issue is irrelevant; who cares if the two shots finally cross at 200 yd, or if their spread reaches 3" at 225 yd... :)

What I can mathematically guaranty you, is that if a double get the two shots touching at xx distance, then by definition it will cross 10 yd beyond and it will shoot a group wider and wider (rights shot on the left of the group and left shot on the right of the group) as distance increases. This is just basic geometry.

I agree here with spike.t and TTundra. I actually prefer a double that shoots 1.5" anywhere from 0 to 50 yd to a double that shoots 0.5" at 50 yd, because the double that shoots 1.5" at 50 yd will likely either continue to shoot 1.5" to 100 yd (holy grail!) or it will get to cross in the 75 to 125 yd bracket, which is good enough for me. Conversely, the double that shoots 0.5" at 50 yd, will cross at 55 and shoot again 0.5" at 60, 1.5" at 75 yd, 2.5" at 85 yd, 3.5" at 95 yd etc. (all these figures are approximations, I have not done the calculus, but you get the point...) :)
 
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One Day...

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upload_2019-12-17_13-2-32.png



How is that for brevity (y)
 

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My Blaser S2 uses ammunition in all three calibers (500-416/ 30-06/ .375) regulated not to cross. It is possible that the 500-416 might, but I have it regulated to a red dot at 70 meters and it prints MOA groups from each barrel creating an overlapping 2.5 inch group - right shots and left shots are separated. The the other two calibers do that at 100 meters and both keep 4 rounds LxR/LxR in 3-3.5 inches at 200 meters with no crossing of the rounds. I obviously use a telescopic sight with both calibers and sight in on the right barrel. The left is always within a MOA or so and always left to at least 300 meters (the farthest I have ever fired at a target).

I have a scoped 9.3x74 German guild gun that does exactly the same thing. So should any properly regulated double.

Unless one is purchasing a new bespoke rifle, regulation is now pretty much a crap shoot. The test target will normally be at 50 meters, and so long as the two test shots are within the target circle - usually three or four inches, it is sent on to distribution. Many test targets are already showing vertical distribution even crossing at that short range.

As @One Day... notes, for most situations, and particularly when using open sights, it doesn’t matter. On the other hand, if one wants a truly versatile double that can pick the odd kudu off the next ridge while trying to walk down a buffalo, it can matter a lot.
 

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Fully agreed Red Leg.

This is where the 500-416 offers a unique flexibility: its .416 400 gr slugs, especially those of spitzer design, will reach out with proper optics.

However, it will do so at the expense of offering less reliable stopping power up close than a .450/.470 rounded or flat nose 500 gr slug.

Compromises, compromises... :)

Compromise as it may be, the 500-416 is likely the caliber approaching the most the mythical "universal" double's caliber, as it shoots 'almost' as flat as the .375 H&H and it hits 'almost' as hard as the .450/.470 NE.

PS: Just like the .416 Rigby (and all its modern Taylor/Hoffman/Remington/Ruger/Dakota/etc. duplications, albeit at significantly increased pressure) truly bridges the gap between the .375 H&H and the .450/470 NE (and their modern .458 Watts/Ackley/Win/Lott/Rigby/etc. duplications)...
 
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One Day...

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One more thought...

We touched above on the effect the higher pressure of hot cordite had on how a rifle regulated in cold England would shoot in hot Africa.

This is a vastly obsolete issue with temperature-stable modern powders, but for complete understanding it is useful to clarify that the critical factor for double rifles crossing or spreading closer or further based on cordite temperature, was not load pressure per se, it was how much AND how long recoil and yaw influenced the direction in which the bullets left the barrels. This is linked to how much time the bullets take to go through the barrels, generally called "barrel time." The same issue still exists today when changing powder type (burn rate) and powder charge (temperature is not an issue anymore).

Two outcomes of higher load pressures are possible:
  • Higher load pressure that does not result in significantly increased bullet velocity will increase the spread of the shots because the barrels will move upward and sideways more (more recoil and yaw) before the bullets leave the barrels.
  • Conversely, higher load pressure that results in significantly higher bullet velocity will decrease the spread of the shots because the bullets will leave the barrels before they fully move upward and sideways.
This is why, I suppose, depending on bullet weight, bullet material and bullet bearing surface, and depending on powders burn rate, some reloaders experience increased spread when increasing their load, while other reloaders experience reduced spread when increasing their load.

For example:
Use only one bullet type, with profile same as originally used to regulate rifle, and later used to re-regulate it by Ken Own. Use only one powder type, R15, unless Ken Owen used a different powder for his regulation load with that given rifle. Don't use 4350 or 4831 no matter where you learned to use them. Don't increase the velocity you shot the 4 inch spread loads with--to increase velocity, all other factors being same, will only increase the spread. Actually, decrease that velocity slightly, hoping for less than 4 inch grouping with left/right barrels. Generally, try to duplicate loads Ken Own used to regulate with, to get same or close to same results as he did.

Since my Krieghoff .470 shoots its regulation load in ~1.75" groups at 50 yards and 100 yards without crossing (left barrel bullets print left of right barrel bullets), and since I therefore do not reload for it, I have never experienced it myself, one way or another, but I figured that mentioning this could further explain the dynamics at play :)
 
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One more thought...

We touched above on the effect the higher pressure of hot cordite had on how a rifle regulated in cold England would shoot in hot Africa.

This is a vastly obsolete issue with temperature-stable modern powders, but for complete understanding it is useful to clarify that the critical factor for double rifles crossing or spreading closer or further based on cordite temperature, was not load pressure per se, it was how much AND how long recoil and yaw influenced the direction in which the bullets left the barrels. This is linked to how much time the bullets take to go through the barrels, generally called "barrel time." The same issue still exists today when changing powder type (burn rate) and powder charge (temperature is not an issue anymore).

Two outcomes of higher load pressures are possible:
  • Higher load pressure that does not result in significantly increased bullet velocity will increase the spread of the shots because the barrels will move upward and sideways more (more recoil and yaw) before the bullets leave the barrels.
  • Conversely, higher load pressure that results in significantly higher bullet velocity will decrease the spread of the shots because the bullets will leave the barrels before they fully move upward and sideways.
This is why, I suppose, depending on bullet weight, bullet material and bullet bearing surface, and depending on powders burn rate, some reloaders experience increased spread when increasing their load, while other reloaders experience reduced spread when increasing their load.

For example:


Since my Krieghoff .470 shoots its regulation load in ~1.75" groups at 50 yards and 100 yards without crossing (left barrel bullets print left of right barrel bullets), and since I therefore do not reload for it, I have never experienced it myself, one way or another, but I figured that mentioning this could further explain the dynamics at play :)
Sounds like perfect regulation for a .470.
 

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