What is the tightest possible rifling?

Question

I was thinking about going into competitive target shooting and was looking into guns and noticed the different rifling ratios. I know if that it is possible to make rifling too tight, but what's the maximum twist possible? If it makes things easier, let's say for a 22LR or a 17HMR.

Answer 1

My 22lr is 1:16 and my 17hmr is 1:9 and those are the only twist rates for those calibers that i know of but could be wrong.

Answer 2

without getting out a slide ruler and physics book...

Bullet weight, length and velocity all factor into the calculations used to determine barrel twist.

The idea is to spin the bullet enough to fly stable along it's path to impact.

AR 15 is a good example. A 1:7 twist will work well with lighter bullets

(55-62 gr if memory serves).. Heavier bullets will be more accurate from a barrel with 1:9 twist.

thats the barn floor version... I am sure someone else will be allong with the equations.

Answer 3

For rim-fire you don't want the "tightest possible twist".

For reasons too numerous to mention, you want the minimum twist

that will stabilize the bullet you're shooting at the velocity you're

shooting it.

Loooong experience has shown that for a .22 R.F. 40 Gr. round,

this is one turn in 12-14".

Don't mess with empirical data, or to put it another way, don't try to re-invent the wheel.

This particular caliber has been around and has been optimized for longer than you've been alive.

Answer 4

And they said I would need to remember that math...

Glad I forgot, It gave me a headache.

Answer 5

You can make rifling as tight as you want. Having rifiling tighter than it should be will have only a minimal effect on accuracy, however, it will cause greatly accelerated barrel wear. If the rifling is too loose, the bullet will tumble and yaw, and accuracy will suffer significantly. Every bullet has an premium rifling twist.

The equation to figure out the optimum rifling twist is:

Twist= ((C)x(D^2))/(L). Where C= a constant equal to 150 if velocity is less than 3000 ft/s or 180 if above 3000 ft/s. D is the diameter of the bullet in inches,  and L is the length of the bullet in inches. There is another part to the equation involving specific gravity if you are using a non lead core bullet, so keep that in mind.

So, with a .22LR, D=.223", L=.395", and C=150 we get a twist of 18.8 or a rifling ratio of about 1:19.

With a .17HMR, D=.172", L=.291", and C=150 we get a twist of 15.24" or a rifling ratio of about 1:15.