5.56 & Barrel Twist .... Stabilization Question.

[RoosterShooter]

I have several 5.56 AR-15s and all of them are 1:7" twist barrels. A friend has a 1:9" Twist 20" barrel that I am considering trading towards a piece of non-gun related equipment that I have.

My question is this:

Ninety percent of my reloaded ammo is either done using either a 75 gr. BTHP or 77 gr. SMK bullet!

Now, I have heard instances where the 1:9" twist barrels would stabilize a 75 gr. bullet, but it was usually in the 22" to 24" varmint barrel range.

I was always taught never to load anything heavier than a 69 gr. bullet for a 1:9" barrel.

Any thoughts?

 

[rsilvers]

Re: 5.56 & Barrel Twist .... Stabilization Question.

1:9 is not really fast enough for 75/77. You may never notice anything though, especially in warmer weather or at higher altitudes. But I would not purposely buy a 1:9 if I wanted to shoot those.

 

[Pusher591]

Re: 5.56 & Barrel Twist .... Stabilization Question.

I have had 1-9 barrels that would and would not shoot 75/77 stuff. If you shoot it loaded to 5.56 pressure it works but if it .223 loaded then it won't.

If your gonna shoot 75/77 grain stuff just get a 1-7 or 1-8 twist.

 

[gstaylorg]

Re: 5.56 & Barrel Twist .... Stabilization Question.

I had a Sig 556 DMR with a 21" 10-twist barrel, it worked just fine with longer (77 gr) loads:

http://www.snipershide.com/forum/ubbthre...625#Post2004625

Much of what you read regarding barrel twist rates tends to be most useful as a guideline or generalization, but is not necessarily written in stone for any given weapon. Case in point; my Sig DMR above.

Having said that, if you know that 75/77 are what you mostly want to shoot, why possibly hamstring yourself by getting a potentially less than optimal twist barrel? A 1:8 or 1:7 twist is not going to let you down with those loads, whereas a 1:9 might. You might get lucky as I did, then again, you might not.

 

[bricktop]

Re: 5.56 & Barrel Twist .... Stabilization Question.

You could always get it and swap the barrel out to a 1:7 for a few hundred if it doesn't work out. Not that difficult to do it yourself in an AR... You might recoup some of the cost by then pawning the 1:9 barrel.

 

[TonyAngel]

Re: 5.56 & Barrel Twist .... Stabilization Question.

As mentioned, it's hit and miss. I now have a Bushmaster 1:9 on a rifle that I threw together and it shoots 77s well enough to hit clays at 100 yards, but the last barrel that I had wouldn't shoot 77s worth a crap.

 

[Bedlam]

Re: 5.56 & Barrel Twist .... Stabilization Question.

Don't do it unless you want a rifle for just blasting away or for dropping a .22lr kit into.

 

[sf88]

Re: 5.56 & Barrel Twist .... Stabilization Question.

I think the question begging to be asked is what is your motivation for switching from a barrel with the optimal twist rate for your reloads to a sub par one?

 

[Asm1]

Re: 5.56 & Barrel Twist .... Stabilization Question.

http://www.hornadyle.com/products/more_detaila4d2.html?id=72&sID=75&pID=2