8 bore bp loads

[¡Señor.Casualidad!]

Como estas mis amigos!?
Iso loads and nerdy info for an 8 bore rifle.
Ive recently purchased an 8 bore pinfire rifle mfr'd by devisme of France circa 1863 and am trying to get any load info I can.
The previous owner slugged to bore but only mentioned the bore dia (.840") not the groove dia. I will slug the bore myself when I get more cerrosafe.
Im aware of typical charges and wad/nitrocard configurations but my question is how much larger than groove dia should the bullet be? Ive always stayed less than .005" over for my sharps rifles, does this also make sense for an .84 cal? The barrel is 27" and has a very fast twist rate of 1:12.
Ive got a bullet mold from the previous owner. Its an accurate molds .89 cal with my ebay alloy it drops a bullet at .888" and 1,490grns the groove diameter mics at .860"-.865" at the muzzle with my calipers. He and I have both shot it with this bullet (moderate loads) and it seems to shoot good! all my knowledge and experience(im a noob) tells me 48 thou over bore diameter is a lot even with deep 10-15 thou rifling. Any info would be greatly appreciated! if I can get this rifle shooting very well and consistent it may join me for my first buff hunt down under. Maybe in a few years!

 

[fourfive8]

Love the old guns! I certainly have no experience with a 86 caliber pinfire! You’re right, that 12” twist is very fast for such a large caliber and obviously calls for a conical. Keep us posted…

 

[Daryl S]

Been shooting lead for many years. I would not go larger than .865".
12" ROT sounds WAY too after to me.
Much also depends on the alloy, of course. Something around 10 to 13 brinel would be about perfect imho.
What exactly are you wanting to shoot with it?
What loads does W.W. Greener mention in The Gun? He notes: 10 drams (273gr.) 862gr. bullet.
No mention is made if this is for a pin fire or central fire gun. but it is listed as .835", which is 8 bore(8 balls of pure lead that size = 1 pound). 7,000gr. divided by 8 = 875gr. for a pure lead round ball. 12" twist is WAY too fast for a short slug or round ball. An 80" ROT might be closer to what is more likely.
7 bore is nominally .873". A round ball of 7 bore would weigh 1,000gr. even.

 

[¡Señor.Casualidad!]

This gun is very interesting to me and really is an odd piece(kinda why i bought it)
Not sure who or what this rifle was originally made for.
3 5/8" chamber nearly 500grn case capacity
1:12 twist
Shortish single barrel
11 lb weight(its been restocked)

If it had a roundball twist rate and a shorter chamber it would make sense. Lightweight (for the bore) single barrel good for crazy stopping power without weighing 15+lbs

But its got a case length for 300+ grains and a twist rate that mathematically would stabilize a 2000+ grain bullet

"Plinking" loads with my current bullet at 550fps and 1000ftlbs of energy will still yield around 90-100 ft lbs of recoil. supersonic loads would be SPICY 250-300 ft lbs of recoil easy

 

[Daryl S]

Yes, that rate if twist has me baffled. I just dont understand it. Now, the slower moving the bullet, the faster the twist must be, but 12" is SO fast for such a big bore. I just dont undrsyand it as it dates past when weirdly fast twists were being used in Britain(percussion era)

 

[fourfive8]

Yikes, plinking load with that much recoil!
Almost sounds like a specialty or custom made gun for DG hunting. Another thing popped into my head was possibility that in an earlier life it was a Paradox? I’d be tempted to lighten the charge down to 50-80 gr FF and work up using variable fiber filler w/o airspace of course. Folliwing…

 

[¡Señor.Casualidad!]

Here is the current bullet

Although the twist is crazy fast it does seem to shoot well. Ive always been under the impression that over stabilization is better than under stabilization?
Currently hits about 2" right at 25yds and about 2' right at 170yds all off hand
bullet seems to fly just fine

 

[¡Señor.Casualidad!]

Been shooting lead for many years. I would not go larger than .865".

I was thinking the same thing once I get the bore slugged ill likely get a different bullet mold.
Probably this one. Weight is a little less so is overall length but the length of actual bullet contacting the rifleing is greater and he can machine the mold to my requested dia for any particular alloy
Would probably do a 1:20 or 1:15 tin to lead, keep it easy