58 cal 20 inch barrel expectations

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david doyle

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Working on a smooth bore 58 cal BP ML with a 20 inch barrel. (not my first choice in length but it had it's merits in terms of $ for barrel and stock and ease of inletting. i.e super nice half stock blank for 70 bucks and 90 dollar barrel )

As I get close to committing to my drop at heel and comb I am wondering what velocity I can expect from a PRB from this tube. I know it is realistically of little importance what sight height I use but I am trying to create the 'perfectly fitted stock'. I want to be able to shoulder it and have it pointing out in space with a 100 yd zero (yes it is all foolishness on this particular gun which realistically will be hunting at bow ranges for grouse with shot)

If anyone has any insight on what velocity I can expect with between 60 grains (what the devenport formula says is most efficient) and heavier charges I would appreciate hearing about it. I can find lots of info on 100 grain charges in 36 inch plus barrels but cannot find any real info on short tubes (wonder why;)

I will use this info to determine the sight heights and the sight heights to determine the stock shape.

Thanks
 
I'll check my Lyman tables when I get home (4 hrs) unless someone beats me to it. I'll give you velocities for the shortest 58 barrel they have listed using a PRB.

PS that sounds like a really cool build...we need pics as you progress.
 
Did a little more research and it seems that the davenport (?) formula indicates a 60 ish grain load of this length of barrel, Goex lists about 1000 fps for 60 grains of powder in an unknown barrel length.
Wow you sure give up alot in a short barrel!

Any ideas about the feasibility of achieving 1000 fps in a 20 inch barrel? I wonder how much noise, recoil and sprayed unburnt powder I would need to cope with in order to squeeze a bit more velocity out of it?

Probably not worth the bother and a 1000 fps will surely topple a deer at 40 yards so I guess I will plan for a 75 yard zero with a 60-70 grain charge. Back to the rasp....
 
Didn't have the greatest of luck (no listings for tactical ML configuration :) )

.58 x 24"(shortest listed) x 48" twist (slowest listed) Pyrodex Select' 276 gr PRB

60gr-1087 fps,724 ftlbs
80gr-1253 fps,962 ftlbs
100gr-1395 fps,1193 ftlbs

*Always cross reference loads*
 
Thanks alot for that. If I can get 1000-1100 fps out of the 'tactical ML' I'll be content with the project. Might get more as it is a smooth bore and that should make it a bit quicker.

Just another few zillion hours of measuring and taking off a bit of saw dust at a time and I'll check in with a range report.
 
My Westley Richards 12 bore rifle only has 24 inch barrels from 1851 so would use 90 to 100 grains of powder with a 750 grain bullet. That is think is 900 to 1000 fps and is consider good for dangerous game, so 20 inch barrel and good charge of powder behind a ball should be good for anything at the distance of the smooth bore gun is good for
 
I guess a 750 grain bullet at almost any speed would be nice to have between you and teeth and claws!

This gun is mostly a learning piece for me but I do hope it will have a place in the hunting arsenal. a 6 pound or less, 35 inch OAL big bore/small game shotgun should find some use.

I have a picture of 18th century German stutzen (sp) rifle with an even shorter barrel in the same bore size so must be able to do something useful with it.
 
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