Correct Ammo forCommon AR Twist Rate

[kwe45919]

Dolomite's touched on this subject many times on here and I've tried to pay attention to it all. However, with all of the information I've read I still get jumbled up on what grain should be used for what twist rate. Well, we all know with people being different, we all set up our AR's a bit different. Some have the "plain jane" with iron sights, others add a reddot and others go for "distance" set ups. So since we all set up our AR's differently for different reasons, I'd like to have a break down OR disscussion on what grain should be used for the twist rate for how the weapon is set up.

Example:

An AR with a 1/7 twist set up for CQB should use what grain for maximum effectiveness and why? Is this set up is not usefull or "safe" to use as a CQB rifle? Compare the same set up with a 1/9 twist.

An AR set up for general plinking or hunting. Advised twist rate and grain for effectiveness.

I know differences in lengths of barrels help/hurt in these situations as well so please discuss the differences for the usefullness of lengths needed to acheive an effective rifle.

Now, to show everyone how big of a fool my ego let me be, my first AR was a pieced together hodge podge of stuff collected from friends and put together. Dolomite helped me get it running absolutly smooth as silk. Now, this thing shoots great at the range. My 100yrd shots have improved with the Aimpoint but I'm using basic 62gr at the range. At home I have a mag full of Sierra 77gr for the bumps in the night. The more I read, no matter what type of bullet I use, it seems my sweet first AR build is worthless in its current state as a CQB rifle. (thank god I have rifles in other twists) Should I put a scope on it and use it more for "distance" or is it a pretty much worthless upper to have built??

I want to understand these issues better so I and others can understand if we build a rifle one way or the other we can still get maxium effectiveness at close range or distance pending twist rate or grain used.

Edited June 24, 2012 by kwe45919

[Guest nowheretobefound]

Instead of getting opinions or having ballistic segments pasted into replies just do a search and you can get all the knowledge you could ever want.

When I give my personal advice at workshops, seminars, etc. it comes down to two approaches depending on the shooter.

1. If you want it for plinking and just some shooting and home/personal defense...it does not matter what you run through it or what your barrels twist is...if it reliably goes bank and is lethal in the range you can be relatively accurate at, that's all that matters.

2. If you plan on tripping it out for competition or you plan on doing the "prairie dog shooting at 500 meters" then I tell them go read, learn and experience everything on their own because for that it's all opinions on what people like best.

[Dolomite_supafly]

For CQB distances twist and projectile weight generally doesn't matter. A bullet will not become unstable within inches of the muzzle. It generally takes some distance for that to happen and that distance will likely be well beyond CQB distances. And by CQB distances I mean less than 25 yards.

I will say you want the least stabile bullet that will fly straight to your intended target though. That way it doesn't matter the type of bullet you are using, FMJ or HP, it will tumble inside of biodegradeable target.

For a 7 twist gun that will be used for CQB I would use the heaviest bullet I can, like a 77 grain. Because it will generally tumble inside of the target and be devastating because the distance is so short there is still a lot of velocity left. As a matter of fact you could use 62 grain at the same distances and although it may not tumble the velocity will fragment the bullet.

For a 9 twist I would also use a 77 grain bullet because it will, without a doubt, tumble inside of the target. And with 62 grain the same can be said as well. And with both bullets the velocity will fragment them.

Now these recommendations are with FMJ bullets.

With modern rounds like the Hornady TAP the twist is not as important. Those rounds will expand, tumble and be very devastating regardless of how fast they are spinning. Even in a very fast twist a modern HP will fragment down to velocities well below what you would find at CQB distances.

For plinking find the bullet you are likely going to use most then choose a twist rate which works well with it. In 90% of the cases I recommend a 9 twist. The reason is they will shoot 55 and 62 grain bullets, the most common. They will also shoot the lightweight varmint type bullets as well as heavier bullets. I shoot 69 SMK's all the time with zero problems.

No matter what when choosing a twist choose the slowest twist that will fire your heaviest bullet. You do not want to overspin your bullets. The reason is when you are spinning a bullet faster than it needs to be then even the smallest imperfection gets magnified compared with a slower twist. Think of it like an out of balance tire, the slower you go the less noticeable it is but increase the RPM's and it gets worse. This is what happens when you over spin bullets as well as the fact centrifugal force can rip the jacket from the core if RPM's get too high.

Dolomite

[thundersnow]

Great answers as usual Msg and dolomite!

Edited June 24, 2012 by thundersnow

[kwe45919]

Dolomite, my questions were answered. The more I read on the subject, it seemed that no matter what grain I was using, a 1/7 twist would do nothing more than pierce through the target vs. tumble after impact out of a 16in barrel and that CQB ranges were out of the question and all because there was no loss of velocity at CQB ranges. I thought but misunderstood that you needed to loose velocity to "accuate" the tumbling effect with a fast twist rate....that's where I was getting confused. Not sure why I was misunderstanding or confusing the information but for some reason I was. Sometimes the more you read and look at technical data, the more crosseyed you get.......

[Dolomite_supafly]

Give me a call tomorrow sometime. I think I may have not been clear. I promise I can be clearer over the phone.

Dolomite