Rifling

[PomeroyFirepower]

Can someone tell me what different rifling do or whats the difference?
I see 1:7 , 1:12, 1:9, and so forth, but I don't know which one is better for which application or accuracy.

 

[kyhunter]

Lets say for instance your speaking of 5.56
1 in 12 twist rate is great for varmint rifles and will stabilize from 35 up to a 55 grain bullet with no problem. Most 62 grain bullets are good to go here as well.

1 in 9 will stabilize most all of the lighter bullets such as 45-62 grain although ive never played with any of the 35-40 grainers and it may spin those apart. This twist rate will handle 69 and 70 grain bullets well and some of the 77 grain bullets.

1in 7 is better for use with 55 and up all the way to the heavy 90ish grain projectiles generally designed for longer range shooting.

1 in 9 is a great do all twist rate unless your shooting a 5.56/.223 at long ranges. 1 in 7 is excellent because you can shoot surplus m885/m193 and heavier ammo as well.

Twist rates vary by caliber but the rates you mentioned made me assume 5.56. A faster twist rate will better stabilize heavy bullets, but too fast can rip the jacket from light bullets at high speeds.

If youre speaking of another caliber we would be glad to help. Here is a well responded to 5.56 question from the archives
http://www.thehighroad.org/archive/index.php/t-158429.html

 

[peacemaker45]

To be a little more basic about it, the designations refer to rate of twist. For example, 1:7 translates to one full rotation in seven inches. At the other end of the spectrum, 1:66 is one full rotation in 66".

As for application, it basically comes down to weight for caliber. Long, heavy for caliber bullets need a faster twist to stabilize. Short, light ones need much less rotation.

 

[MistWolf]

Actually, it has to do with bullet length and shape, not weight. For example, a VLD (Very Low Drag) bullet made of solid copper will be lighter and longer than a round nosed bullet with a lead core and copper jacket but the round nosed bullet will not need as tight a twist to stabilize. This is because the aerodynamics of a long pointy bullet make it inherently more unstable in flight so it needs more gyroscopic force to keep it point on to it's target in flight.

kyhunter gives a pretty good summary, however. The lighter bullets will do fine in a 1:9 twist or even a 1:7 twist so long as the jacket is tough enough to withstand the RPMs. For a modern 5.56/.223, a 1:9 twist will work well with most 55 gr bullets and sometimes with some of the longer ones, especially if it's a 20" barrel. For carbines, because the shorter barrel generally produces less velocity (thus imparting a lower RPM to the bullet) a 1:7 or 1:8 is a better choice.

The caveat is, every barrel is a law unto itself. You can take two barrels that came down the same assembly line, one right after the other, made to identical specs and have one that will shoot longer bullets well, the will not and vice versa