BP twist rates question

[chainsaw]

I am very new to BP but not so much modern rifles.My question is about rifling twist rates,seems they are way different than modern rifles.Is the basic principal the same with BP as modern?I am looking into getting a .50 cal BP and would like some more info on twist rates recomended for different weight and styles of projectiles.
any replies are appreciated.

 

[zimmerstutzen]

shallow fast twist is for bullets. 1:36 and faster, Deeper slow twist is for patched round balls. over 1:60 Deep fast twist is generally for pistols with patched round balls, 1:20 or for small caliber rifles, 1:30.

 

[mykeal]

There are essentially 3 'ranges' of twist rates appropriate to black powder guns: fast, medium and slow.

Fast rates are similar to those found in modern cartridge guns, usually about 1:20. Like their cartridge counterparts, they are intended for longer, conical shaped projectiles. These rates are almost exclusively found on guns we do not discuss on this forum, popularly known as "**-lines".

Medium rates are on the order of 1:48 and are considered a compromise that can work with either conical bullets or round balls. Many modern factory sidelocks use this twist range. Like any compromise, you do lose some performance but gain flexibility in the choice of projectile.

Slow rates are essentially for round balls and are on the order of 1:60 to about 1:72. They do not spin a conical fast enough for it to achieve stability but do a good job of stabilizing round balls.

 

[Joel/Calgary]

One thing to bear in mind is that optimal twist rate is caliber-dependent and muzzleloaders vary through a wider range than is common in centre-fires. 1:48" is considered a medium or a compromise twist in middling bores - say .45-.54, but it is slow roundball twist in .32. and it's probably a rather fast twist in larger bores, say .69 and up. This has been discussed here fairly often and the Greenhill formula usually comes up, so a search on the forum, as well as on the WWWeb, for "greenhill" should prove informative.

Regards,
Joel

 

[nkbj]

Visiting the website of various manufacturers of muzzleloading and cartridge blackpowder arms is probably the very best way to determine what works.
You might try comparing the twists of long range competition rifles with minie ball rifles, conical rifles and round ball rifles. And, consult the historical sources available online for records of those long ago developing the technologies. It's really a fascinating journey of discovery if you're so inclined. Turns out that the design of the projectile nose, base and lube grooves can determine the twist required as much as the weight and length. And, then as now, what is marketed is a compromise between what would be perfect for the intended use and the practicalities of manufacturing.

 

[ebiggs1]

I would look at it this way, if I knew I was going to shoot nothing but patched round balls, I would buy a 1:70 ROT. But on the other hand, if a good deal on a 1:48 ROT came my way, I would buy it and not think it a compromise at all.
If you know you are only going to shoot those long bullets you better find a faster twist barrel and not buy the “good deal” 1:70 that came your way.

 

[BrownBear]

There's fruitful reading for you and the gleanings of many decades of actual shooting experience going on right now in this thread over in the flintlock rifle section.

Opinion and reading "research" are cheap confetti on the web, but it's not often you get so much actual experience discussing the question of twist rates and accuracy. Not a formula to be seen, yet really fine insights based on decades of thoughtful holes in paper.

 

[Dphar]

I am very new to BP but not so much modern rifles.My question is about rifling twist rates,seems they are way different than modern rifles.Is the basic principal the same with BP as modern?I am looking into getting a .50 cal BP and would like some more info on twist rates recomended for different weight and styles of projectiles.
any replies are appreciated.

For bullets the twist must be sufficient for the length of the bullet. A long 45 caliber bullet, 3 1/2 calibers long perhaps, will require a 18" or faster twist. Bullet WEIGHT itself does not determine twist. Its the LENGTH.
A short bullet, perhaps a 30-36".
Round balls shoot very well from a wide variety of twists and its really not critical.
A 66" twist will be just as accurate as a 48"
I like 48" twists in many calibers but use GM barrels for the most part and thus I use the twist they make.
However, large bore RB rifles (over .69 caliber) shooting heavy charges of powder my prefer twists of 6 ft or slower since the larger balls have much more rotational inertial and may not want to spin up fast when using a patch.

Dan

 

[nkbj]

Some examples of projectiles and twists.

 

[Danbo]

Mykeal, I sort of know what you mean by stabilizing round balls but I also sort of think they don't need stabilizing in the same context as conical bullets. Bullets need it because CG and CP are dislocated unlike round balls. RBs benefit from spin but for different reasons.

Danbo