round ball stabilization

[eph289]

I have a ultri-hi percussion single shot pistol with a 10 in. barrel 45 cal.and 1 in 66 twist. It groups real good with a round ball and 25 to 40 gr. of fff. Why? I thought 1 in 66 was much too slow for a pistol. I'm familiar with the greenhill formula as it pertains to conical bullets. It does'nt consider length of barrel or velosity. Does round ball need a different formula for stabilization?

 

[Norskie]

I'm not familiar with that pistol. Are you sure the twist is that slow? Roundballs are inherently the most stable projectiles that we shoot, so perhaps that's working in your favor.

 

I made a 12' barreled pistol from an Ultra-Hi (Miroku-Japan).45 rifle barrel. It is very accurate with PRB & 35gr 3f. It is 1:48 twist. Bill

 

[JIMinPHX]

Round balls work with the slowest twist of any projectile that I know of. You can do a Google search on The Greenhill Formula (T x L = 150) for a more detailed explanation.

 

[WV_Hillbilly]

I have a ultri-hi percussion single shot pistol with a 10 in. barrel 45 cal.and 1 in 66 twist. It groups real good with a round ball and 25 to 40 gr. of fff. Why? I thought 1 in 66 was much too slow for a pistol. I'm familiar with the greenhill formula as it pertains to conical bullets. It does'nt consider length of barrel or velosity. Does round ball need a different formula for stabilization?

I had a really lengthy reply written that got into lots of related subjects and offered a sort of explanation for what seems to be a paradox (not the gun) in some muzzleloaders. But the best thing I can say is, "Don't knock a good thing!"

Just take advantage of your good fortune. Your's isn't the only gun that works that way, but some do work better than others.

Regards, and shoot safely!
WV_Hillbilly

PS I've always used the same Greenhill formula for the roundball--and there IS consideration for velocities that exceed 2800fps (the factor used is 180 instead of 150). There aren't any muzzleloaders exceeding 2800fps that I know of... I think that modification was intended for the (then) new line of cartridges that were breaking that speed mark. It really does take very little rifling twist to stabilize a round ball--much less than the Greenhill formula would imply., You could probably use a twist that's about 30-50% slower than calculated, and it would still work fine for round ball use--maybe even better...

 

[eph289]

WV hillbilly Thanks for your reply. It inspired me to google up (greenhill round ball). I then clicked on wosika (http//www.leverguns.com/articles/wosika.htrn) I do'nt know what all this means. As I'm computer illiterate,but any way I think it answered my question. It's a very lengthy article by Ed Wosika and it's a brain buster for me ,but it's worth reading.