barrel twist rate question

[DrBaker]

I searched a few other boards and found this to be a very sensitive topic for some individuals. Therefore, I didn't want to ask my question on those forums and start World Thread War III.


AR15... All of mine have 1:9 twist rates. Most of the time I use 55gr ammo. I don't shoot people with my AR, nor do I hunt with it. Most of the time a stare/admire them, take some photos, and occassionaly pull the trigger at some paper targets.

I've been looking for parts to build another. Many of the barrels that meet my price/configuration requests have a 1:7 twist. Based on my usage (or lack of) what should I expect with a 1:7 twist.

This question is asked all the time and nobody seems to have the same answer. My studies find most to say that the faster twist is best for the heavier round. What weights does each twist support? Who do you believe.?.

 

[okgr8outdrs]

I'm sure you have seen this already, but it makes sense to me.

From the AR15.com ammo oracle...

Q. What twist rate do I want for my rifle?

Probably 1:9, but it depends on what kind of bullets you intend to shoot.

Special purpose rifles often have uncommon twist rates. For example, if you are building a varmint rifle and want to shoot the short 35 grain, 40 grain, and 50 grain bullets, a 1:12, or even 1:14 twist would be best. On the other hand, long range High Power shooters often select 1:8, 1:7.7, 1:7, or 1:6.5-twist barrels to stabilize the long 77, 80 and even 90 grain bullets used for 1,000 yard competition. Additionally, new testing of heavier rounds (68-77 grains) seems to show that they perform very well in simulated tissue and may be a better defensive choice than 55 grain or 62 grain rounds. The majority of shooters, though, typically shoot bullets of 50 to 69 grains in weight (note that the 62gr SS-109/M855 bullet is as long as a 71 grain lead core bullet) and should select 1:9 twist barrels. At typical .223 velocities, a 1:9 twist will stabilize bullet lengths equivalent to lead-core bullets of 40 to 73 grains in weight.

1:12 twist rifles cannot stabilize SS-109/M855 bullets and 1:7 twist rifles are slightly less accurate with lighter bullets and will often blow apart the thin jackets of lightweight varmint bullets. The 1:7 twist is used by the military to stabilize the super-long L-110/M856 tracer bullet out to 800 yards, but unless your plans include shooting a significant amount of M856, the 1:9 twist rate is better suited for general use.

There is, of course, an exception: if you want to use loads utilizing the heavier, 75-77 grain match bullets currently used by Spec-Ops troops and other selected shooters, you'll want a 1:7 twist barrel. Although military loadings using these bullets are expensive and hard to get, some persistent folks have managed to obtain a supply, and will need the proper barrel twist to use them. Anyone who foresees a need to shoot this ammo should consider a 1:7 twist barrel.

 

[tdking]

Any twist from 1 in 9" to 1 in 7" will shoot fine with any bullet weight from 35 grains up to 70 grains. If you ever want to shoot heavier bullets you will need a 1 in 8" twist or faster. Some people think the accuracy with light bullets suffers with faster twists. I know too many good shooters who can shoot 1/2" groups with any weight bullet from a 1 in 7" twist barrel to believe that. The faster twist will only be less accurate if you are shooting a benchrest accurate gun (sub 1/5 MOA).

Theron

 

[DrBaker]

Thanks for the info.

Does the length of the barrel make any difference? I'm looking at a 10.5in barrel in 1x7 to use with 55gr.

 

[grwd]

1:7" twist is optimal for 62gr bullets, and the heavier 70-77gr bullets will work well with them also. USUALLY, the 1:7" barrels are preferred for an M4gery build, because of their ability to shoot the more current heavy military ball ammo, like that black hills 77gr. stuff.

-but out of a shorter barrel, like 10.5", youre not necessarily going for high accuracy anyway, so use what ya got. -usually 1:9" twist barrels are cheaper and would work fine.
And Im guessing that a slower twist could prolong a barrels life, if you plan on wearing it out.

 

[grwd]

OH; and TDKING,
EXCELLENT FIRST POST! Welcome to OKshooters.

Stick around, we need sources of good information !

 

[wps]

When talking twist rates, and bullet weights I think it's important to seperate military versus civilian bullets.

The post from the ammo oracle above addresses some of this.

Military bullets are more forgiving with varying twist rates, so one could get by with 1/9, or 1/7 on most available military ammo.

Lighter weight civilian (commercial) bullets can work on a 1/7, but this is very dependent on jacket thickness. If the jacket is thin the bullet will probably disentegrate shortly after it leaves the barrel. I shoot both 50, and 52 grain varmit bullets out of my 1/9, and I get occasional disentegration even with this twist, so a faster twist in this case just wouldn't work. 40 grain bullets don't work at all in my barrel. I just as well throw rocks at the target.

I think some barrels just prefer some bullets over others.

All this is just my opinion from field tests, which are far from scientific in my case.

WPS.

 

[12gabackup]

If I'm not mistaken, the heavier bullets were developed for longer range stabillity. I've got a 16" Wilson 1 in 8 twist bull barrel that likes 55-62gr. bullets really well. On a good day it will shoot 1/2" moa.

 

[OStateFlyer]

'm looking at a 10.5in barrel in 1x7 to use with 55gr.

Mk18gery?

 

[DrBaker]

Mk18gery?

Call it what you want. I call it pimptastical.