minimum ball rotation

[2 shots]

hi, so a 1 in 66 barrel rotates the ball 1 turn in 66 in, 1/2 turn in 33 in. 1/4 turn in 16.5 in. ect. my question is how short can a 1 in 66 barrel be and still be accurate? or what is minimum amount of ball rotation needed ?

 

[BruceHH]

Depends on a lot of different things. A short pistol barrel is accurate, but usually only for a shorter distance. That could be because of the sight radius or maybe the short barrel. Once a ball is spinning, it is spinning. All of us have seen smooth bores that had some decent accuracy - again out to a certain distance. The only way to know for certain how barrel length would be an issue with twist/spin is to take a new certain length barrel, put it in a steady vice or shooting rack, fire it a lot to get the standard and then cut off a few inches and repeat and so forth until you have a nub. Then you would need to do a whole bunch more barrels and different calibers/twist rates to compare to see if you can get statistically similar results. This has actually been done on modern rifles and if my memory is correct, they found either 16" or 18" was about where they documented accuracy began to fall off.

I believe a lot of shooters have some accuracy loss that is caused by overly hot loads. Pushing a ball/patch too fast can cause the ball to skip over the lands and grooves - in my unqualified opinion. I have done some of my best match shooting with a shorter barrel (26"-28") with a light load, but there are many other factors that contribute to that such as caliber, twist and rifle weight.

 

[Absoroka]

I don't recall where I read it, but do remember reading of an experiment that involved cutting off the barrel in measured lengths until the accuracy began to suffer. Not sure but seem to recall the twist was 1 in 48 and the results noticeably deteriorated below the 28 inch barrel length. They also noticed a significant drop in velocity below that barrel length (no surprise with black powder).

 

[Matt85]

All other things being ideal, barrel length has nothing to do with accuracy. There are videos of people with "unmentionable" firearms that have 1.75" barrels repeatedly making incredibly long range shots (300+ yards). You need enough barrel to put a spin on the projectile, which can be a very very short barrel.

 

[2 shots]

im thinkin our slow twist barrels would differ.. ie. 1 turn in 66 inches vs one turn in 8 or 9 or 12 inches.

 

[64Springer]

When I test fire my 18.75", 1:66, .45 barrel I'll let you know.

I have no doubt it will shoot accurately.

The 2-7 power scout scope will not let me down.

 

[2 shots]

thanks 64springer.

 

[64Springer]

Need a break in this cold weather.

Excited to take her for a spin.

 

[Dartwick]

Barrel length has NO relation to twist rate.
That rifling will impart its spin whether the barrel is 16 inches long or 50 inches long.

Proper twist rate is mostly determined by 3 factors
-Bullet diameter - fatter bullet requires slower spin
-Bullet length - longer bullet requires faster spin
-Velocity(but its actually RPM that matters.)

Velocity only matters in that increasing velocity in given barrel increases RPM.

An example here lets compare a PBR and PA conical.
If a PBR shoots best in a given barrel at a given velocity chances are the PA conical will shoot its best at a slightly higher velocity - thats because the conical is functionally longer.

 

[longcruise]

All my guns prefer Coors.

 

[Col. Batguano]

1/4 turn seems to be the number used for very short pistol barrels, like .38 snubbies. ML'er pistol barrels typically have a faster twist rate than rifles in the same caliber.

 

[64Springer]

All my guns prefer Coors.

Bu-Dum-Tis.

 

[M. De Land]

1/4 turn seems to be the number used for very short pistol barrels, like .38 snubbies. ML'er pistol barrels typically have a faster twist rate than rifles in the same caliber.

The problem is comparing conical bullet stability requiring far more spin than does round balls which is what is being used mostly in revolvers or single shot hand guns for target shooting.
I made a percussion horse pistol with a nine inch barrel in .54 cal cut from a rifle barrel that has one turn in 60 inches. I have tested it to 50 yards from a bench using round patched ball and I was amazed how accurate it still was . The only accuracy degradation I could see from the short barrel was the shorter sight radius and inability to hold it as firmly as could be accomplished by a rifle stock.

 

[2 shots]

thanks m. de land, thats the type of info i was looking for. so that ball was getting less than a 1/4 turn in that barrel and still accurate.