I was aware of this but I allways wondered if accuracy and performance was affected? Perhaps some one with some experience will share their knowledge?
SWARA, The load that gave over 2200fps was the Woodleigh 500gr PP which is longer than the round nose in the same weight and was pretty heavily compressed. I didn't mind because I don't really have a problem if a load is compressed but I know that some people do. The load that I gave above, using the Woodleigh 480gr RN wasn't heavily compressed - in fact there was very little compression, just a tiny bit enough to stop the powder from freely moving. This load also was spot on at 2150fps which was always considered to be the 'magic' velocity that people were after. If someone doesn't like heavily compressed loads, I can highly recommend the 480gr Woodleigh RN. Good hunting to you too.. Russ.
From what I've read, people seem to lose about 50-100fps shooting the shorter Win Mag in the Lott chamber...
If you shoot a WM cartridge in the Lott, wouldn't the extra chamber space just act like freebore, at least theoretically increasing velocity, if not accuracy?
Freebore decreases velocity because it allows some of the initial pressure to push past the bullet. The theory is that by allowing the initial pressure to pass, thus decreasing the pressure at that point, which is at the peak point of pressure, that the powder charge can be increased so that there will be a longer duration of pressure resulting in higher velocity. But with a given load comparing a cartridge fired in a non-freeebore with a freebore chamber, the non-freebore is more efficient and will have higher velocity.
There seems to be two schools of thought, leading (pun intended) to claims that freebore increases and decreases velocity. "By adding more free bore, the bullet is then able to be seated out further thus increasing the case capacity which in turns allows you to add more powder to the case and thus an increase in velocity, usually quite a substantial increase in velocity at that." http://www.gunnersden.com/index.htm.rifle-barrel-free-bore.html
It isn't two different theories- it's how the barrel configuration is used. With bullets seated to the "normal" OAL there is the blowby space I previously described, allowing for reduced initial pressure and for increased powder charge. Or by seating a bullet far enough forward that this blowby space is filled the freebore space is eliminated and the bullet seals the barrel in the same fashion as a normal OAL in a standard chamber. Since the bullet base is well forward in the cartridge, there is increased powder space so the effect is to make the cartridge perform as if it were a larger case. The results being similar to an "improved" case with a no freebore barrel.
Ray , Roland , I suppose it only makes a difference if the operator uses that extra space made available by seating the bullet further out in the case to add more powder??? But with factory ammunition probably as Bad Boy said ..a loss 50ft/sec or so. And really if you owned a 458 "Lott" why would you realistically load up 458WM to take advantage of the free bore unless you where in a pinch? Would you not just load up Lott and go? still interesting though .
The factory .458 has a LOT of freebore - to much to be honest. Duane Wiebe wrote how he fired some factory ammo in a .458 and it chrono'd at 1900fps. He then took a thread off the barrel and screwed it in to remove the freebore and the velocity jumped to over 2000fps! The limiting factor with the .458 has always been the magazine length - not the throat length. IMO it would make more sense to have the throat length a similar length to the mag length get rid of some of the unnecessary (IMO) freebore...
Wasn't aware that was the reason for less velocity with more free bore. I've always thought it was pressure related where the more freebore delayed the bullet contact with the lands thus increasing the initial internal volume of the combustion chamber as the bullet moved forward with no resistance from land engagement just after ignition thus lessening the starting peak pressure thus reducing the velocity. Nothing to very little to do with gases blowing by the bullet. Freebore is why Weatherbys do what they do with loads that would otherwise run over-pressure. Another way to approach regaining cartridge potential or "normal" velocity as with the greater freebore of a WM in a Lott chamber would be to use a slighty faster powder - that would increase initial pressure thus the velocity. Or as was discussed somewhere, simply seating the WM bullet out farther then increasing powder charge. However... much of the discussion about the options for various seating depths is academic because of the location of the crimp groove and the necessity for a solid crimp in most heavy recoiling rifles. Of course recoil induced bullet "set back" wouldn't apply to a single shot as it certainly does in a magazine bolt gun. And recoil induced bullet "pull" would apply to a double rifle.
The challenge with the .458 WM has always been case capacity. Compressed loads lead to caking of the powder and potentially part ignition and squib loads. As a PH, I'd load my ammo fresh every year in my .458 WM. The only rifle I used consistently over a 20 year career. Never an issue and never a failure. The Lott has a lot more case space and thus no need to compress the load. If you're hand loading your own, very little freebore is left ideally. The velocities from the .458 and Lott compared are quite significant. We have a new player on the block now too... the .458 African.
I recall reading somewhere that freebore increases velocity by giving the bullet a running jump at the lands, the bullet's momentum helping to overcome resistance from the lands. But I am unable to Google up any authority for that proposition, so maybe my memory is in error. Maybe I read it in some old Weatherby ads. Surely Weatherby has some reason for the freebore, beyond simply burning more powder, and the obvious reason that occurs to me is Weatherby must believe freebore increases velocity. Even if the running-jump theory is poppycock (or an invention of my subconscious), isn't it possible the greater powder capacity that freebore allows for does increase velocity, at least a smidgeon? If so, then one might say that freebore increases (allows for greater) velocity.
Id be surprised if it was otherwise , your job as a PH isn't to be dropping game (firing rounds) it's first to see that your clients come home in one piece, second to blah blah blah... Not diminishing your job in anyway. But most folks forget in the protection part. And to be good at that part you need to be fast and accurate with your rifle....lots & lots of range time. (apologies a bit of topic of this thread)
That about sums it up! @HWL , if you're wanting to convert one of your 458 WM rifles to 458 Lott, I say go for it. Why not? It isn't about practicality, nor need, but want. So, why not? Go for it. Have some fun.
