HELP with Barrel twist on ar-15

ArmaliteA4

I have a pre-ban in m-4 configuration. I do not know the twist rate for sure, BUT 98% of them are 1/9 twist. Now , my problem. I was shooting at my range yesterday, with this rifle at 100 yrds. The ammo was m855 green tips with a 62 gr bullet. This is what this rifle was designed to shoot. The PROBLEM is that at 100 yrds the bullets were yawing pretty bad and rather than a neat hole I was looking at hourglasses. Unless I am informed incorrectly, a 1x9 barrel will easily stabilize this bullet and go up to the 69 grainers pretty easily. Do I need a different upper of just twist rate barrel. I was thinking about possibly getting a 1x7 but they are kinda hard to find in the 16in. m-4 style. Thanks for any input

Contender Man

Have you recently acquired this rifle?

Any problems w/ lighter bullets?

How's the bore?

Have you tried any other ammo in that weight range?

I agree that a 1:9 should do it with no problem unless the barrel has a problem.

Short of making a "bore slug" a down and dirty way of trying to determine the twist would be to take a new bore brush and using an extra long cleaning rod with the shaft taped off well back from the chamber, draw a line to use as a rotation reference then scribe the length of the tape in 1/2 inch increments. Get the brush fully into the bore then advance it until you have one full rotation and note the distance traveled. Do this 2 or 3 times to make sure your rough measurement comes out about the same.

Of course if you've got a gunsmith that you use and don't want to mess with all of the "hocus pocus" take it to your "smith" and he shouldn't charge very much for making the determination.



If you only have time to do two things so-so, or one thing well ... do the one thing!

temblor

1x9" should work fine for the 62gr just as you stated and in most cases work on the 69gr as well. I suspect it is a slower twist rate like a 1x12" or 1x14" but you need to determine for sure as Contender Man stated above. Also have the crown on the bbl checked. If they are dinged badly they will sometimes do strange things to bullets.......good luck.........[8D]

ArmaliteA4

Thanks guys..
I called a master armorer in my area. I am taking it to him to check out. Worst case , I buy a new pre ban upper. Thanks again[;)]

Jim Rau

You did say pre-ban so you could have the slower twist. Put a tight fitting cleaning rod w/patch in and push it in until it rotates once and measure the distance and you will know for sure.[^]

Self defence is an ablsolute and natural right. Keep your powder dry! J. Rau, Alaska

v35

I believe 1 in 9 twists came a bit later. You probably have a 1 in 12 twist.

Txs

Is it not stamped on the barrel just forward of the front sight?