Pistol twist rates

[longcruise]

I'm wondering what the serious cap and flint pistol shooters are using barrel wise. It seems that the popular barrels available for pistols are in the faster twist category.

Question is; do these shoot better than a pistol barrel with a twist rate comparable to a rifle twist rate in the same caliber. Eg., 1/48 for a .45, 1/60 to 1/70 for the .50 to .58 cal pistols?

I'm planning to build a cap or flint pistol and while I won't be using it in competition, would like to have max accuracy for small game hunting, etc.

 

[hanshi]

I'm no expert but since a pistol ball travels much more slowly than a rifle ball, the twist rate should be faster than a comparable rifle. I know of pistols built from rifle barrel sections and the accuracy was disappointing.

 

[RADeO]

Specs I've read regarding pistol barrel twist rates range from 1 turn in 18" to 1 turn in 22".

I'm no expert but since a pistol ball travels much more slowly than a rifle ball, the twist rate should be faster than a comparable rifle. I know of pistols built from rifle barrel sections and the accuracy was disappointing.

Hanshi is right on both counts here! I know from experience about using a section of rifle barrel for a pistol. It worked, but not nearly as well as I had hoped.

 

[longcruise]

Good info guys. :applause:

Using a section of a rifle barrel is exactly what I had in mind. I'm going to go ahead with it for a current project, but when I build my "tack driver" :wink: It's going to be a dedicated pistol barrel.

 

[Zonie]

Your pistols short rifle barrel will at least be as accurate as a patched ball in a smoothbore and probably more accurate.

 

[Ken Rummer]

Lyman GPP is 1:30 in both 50 and 54
Traditions KY is 1:20

Got all three. The GPP in 54 shoots best, 1" at 25 yds. Others are nearer 2".

I think using a rifle twist will give groups that look like you used a scattergun.

 

[rafterob]

A pistol will need a faster twist rate because of the much shorter barrel, in order to impart an effective twist in a short distance. My Kentucky pistol has about 1/4 twist in 9 1/2" or roughly 1:38. It is very accurate. If you cut a 1:48 rifle barrel down to 12" that would give you 1/4 twist and I think you would be ok cutting to 10". If it was me, building from scratch I would go 11 or 12 inches. Also check your hunting regulations on what is allowed.

 

[wildeagle]

This reply is to any and all. I'm having a hard time wrapping my small noggin around this. If the rate of twist is one revolution in x number of inches, how does the length of the barrel affect rotation of the ball. If the rot is 1 in 10 will it not be the same out of a 10" or a 20" tube? My mind tells me that once a ball starts to rotate at a given spin it continues at that rate. I was thinking that progressive rifling could maybe change the rate of twist but normal rifling would would maintain constant spin at 4" down the bore or 14"down the bore. I always thought that lesser accuracy of pistols was due to the short sight radius. Please be gentle with me,my feeble brain is hurting from pondering this discussion :surrender:

 

[R.M.]

No, you are right. The barrel length doesn't change the twist rate. What it does do, is develop higher velocity, thus higher RPM.

 

[wildeagle]

Ok, I get that, but if velocity is increased and the rpm's, won't the distance ball covers correspond to the rate of twist?

 

[fyrfyter43]

Yep, the rate of twist doesn't change. If a barrel is rifled with, say, a 1 in 48" ROT, the ball will make one complete revolution in 48" of linear travel, regardless of barrel length.

Since a ball from a pistol is travelling at a lower velocity, it requires more stabilization (faster rate of twist) to remain stable in flight. The higher velocity of a ball from a rifle requires less stabilization.

 

[wildeagle]

:thumbsup: I do know there are alot of variables involved here, but things are already starting to come in to focus. :haha:

 

[Jim/OH]

I am afraid you are going to be really disapointed with a cut off rifle barrel. I tried it too on my first pistol, and is simply is not good. About all you can say is it does go "bang". But hitting anything is a real challange. Shooting an accurate pistol is a load of fun, and very satifying, but a bad shooting one can bring on frustration. That can cause you to lose interest in a sport that is really fun. Good pistol barrels are not that expensive and well worth the cost. Hope this helps. :thumbsup:

See ya, Jim/OH :hatsoff:

 

[hanshi]

Good info guys. :applause:

Using a section of a rifle barrel is exactly what I had in mind. I'm going to go ahead with it for a current project, but when I build my "tack driver" :wink: It's going to be a dedicated pistol barrel.

Have you thought about removing the rifling and making it a smoothbore? I wouldn't mind having a nice little smoothbore pistol, myself. If it's a smoothy the barrel wouldn't have to be very long at all and you could build a smaller, handier pistol, perfect for riverboat gambling with cheaters, chasing off miscreants getting fresh with ladies and delivering a coup de grace to wounded deer. :rotf: Serious about the smoothy, though.

 

[mykeal]

Let’s do the math::

In an 8” pistol barrel the ball accelerates from rest to a muzzle velocity of (for example) 925 fps or 11,100 inches/second, assuming a .490 patched round ball and 50 grains of black powder. It is in the barrel 0.001441 seconds; I’m assuming a linear acceleration, which is not accurate but makes things easier. With that assumption we can use 5550 in/sec, half the muzzle velocity to calculate the time it takes to travel 8 inches, thus 8/5550=0.001441 seconds. Assuming a 1:30 ROT, the ball rotates 96 degrees in 8 inches ”“ (8/30)*360=96. Rotating 96 degrees in 0.001441 seconds is (96/0.001441)*60=11,100 RPM.

In a 28” rifle barrel the ball accelerates from rest to a muzzle velocity of 1,100 fps or 13,200 inches/second assuming the same .490 patched round ball with 50 gr real black powder. In this case it’s in the barrel 28/(13,200/2)=0.0042 sec. Assuming a 1:60 ROT, the ball rotates (28/60)*360=168 degrees; 168 degrees in 0.004242 seconds is 168/0.004242=110 deg/sec or 6600 RPM.

If the rifle had the same twist rate as the pistol the ball would be rotating at 13,200 RPM.

 

[Dphar]

Lyman GPP is 1:30 in both 50 and 54
Traditions KY is 1:20

Got all three. The GPP in 54 shoots best, 1" at 25 yds. Others are nearer 2".

I think using a rifle twist will give groups that look like you used a scattergun.

I have made several pistols with cut off rifle barrels. Used to be all there was aside from ordering something custom.
A 50 with a 66 twist will shoot fine for hunting even with a short 6" barrel. I have killed small and big game both with rifle twist FL and percussion pistols.
I built a pair of pistols, 6", from one 12" GM 22" twist 54 pistol barrel and I was not impressed with the accuracy. But I did not try really light loads using about 35-45 grains.
I have a 54 with a 66 twist under construction that should do as well as the last 66 twist 54 I built. It would knock over the little buffalo silhouettes (size the the NMLRA Buff target out) every shot at 75 yards and with a solid rest would shoot under 2" at 25.
The round ball needs very little twist to be accurate but it requires load development just like a rifle and some pistols with rifle twists might need a heavy load, 60 grains or more in a 54, to shoot well. Just like some rifles and smoothbores need heavy charges.
If you want a hunting pistol a fast twist may not be the best choice. Though a 30-48" might be better than a 66 I do not know, never built a 30 or 48 twist pistol. Since a 48 will work well in rifles it should work fine in a pistol as well.
I think the 22" should give very good accuracy with the proper charge or powder but I am not sure it will shoot well with heavy loads in larger calibers.
This is the ball and front leg bone from a doe Mule Deer killed with a 70" twist 54 caliber percussion pistol. Ball broke the bone and took out the heart was under the far side hide.

Dan

 

[necchi]

Once it leaves the barrel, no matter it's RPM, Gravity and air resistance take over. I always thought the reason to spin a ball/projectile in the first place was to make it travel through the atmosphere better than no rotation at all, thus more accuratly :hmm:

 

[wildeagle]

Yes, I agree there are external factors, but what takes place inside the barrel has a great effect also. I thank you all for the replies, things do make more sense now. I guess the length of the barrel is important in that this dictates how much energy is generated. One could compensate for lower velocities by adding more powder to the charge, BUT that would create an unsafe condition. So by tweaking the rifling's rot you gain the stabilizing effect with the same charge. See I told you things were starting to come into focus, BTW I was terrible at math :redface: , way back when I was in school, so that post kinda left me foggy but I still appreciate you trying to set me straight. :bow: And thanks for being gentle. :haha:

 

[Zonie]

wildeagle
YOur on the right track about power and twist. Your even closer if you substitute velocity for "Power".

The thing about pistols is their short barrels limits how much velocity can be gained by just adding powder. After some point, because of the short barrels the extra powder won't add much if any more velocity because the ball is already headed downrange out of the barrel while the extra powder is still burning.

As for the velocity of rotation or spin needed for a roundball, it isn't that much.

With an elongated bullet a high rate of spin is necessary because if a low spin speed is used the bullet will not be stable.
With a low rotational speed a elongated bullet will actually start tumbling end over end. This sort of thing is visable on a target because of the elongated hole, often called a "keyhole".

With a roundball fired from a smoothbore, the very high speed air will make very small irregularities on the balls surface, or small out of round shape variations of the surface have different pressures pushing back against the ball.
These different pressures will deflect the non-spinning ball in unpredictable directions. Sometimes up, down, right, left or a combination of these directions.

If the ball is spinning very slowly, the deflections will still occur.

If the ball is spinning fast enough, the spinning balls irregularities will have moved fast enough to a different place so that the direction of the pressure deflection becomes pretty much equal in all directions.
When this happens, the ball will not be deflected by the pressure differences.

Then, it is just a matter of the wind slowing the velocity and gravity pulling the ball towards earth.

All of this explains why barrels that are made for shooting roundballs can have much slower rates of twist than a similar caliber that is made for shooting elongated bullets.

 

[zimmerstutzen]

I've had fast twist, slow twist and smooth bore barrels on pistols. A fast twist shoots more accurately. However, you have to be a heck of a steady hand to see the difference with standard one hand hold shooting. A smoothbore is almost as accurate as a rifled barrel at 25 yds. An acquaintance of mine won a lot of matches with a short stubby 20 inch 357 barrel on his rifle. He'd only shoot about 10 grains with a tight patched round ball and won alot of short range matches. 25 to 50 yds.

In the over all scheme of things, the grip, balance, sights, muzzle crown, load, patch ball combo and trigger pull make as much difference as anything. If you have the best possible combo of these, then perhaps the rate of twist will narrow your group.