80 gr. SMK & twist rate

R

Roy Allain

Guest
I have a AR-15 with a 1:9 twist. I need to know if I can shoot 80 gr. SMK bullets with a reasonable degree of accuracy. Most places I looked at say up to 70 grs. for the 9 twist. A couple say 80 is ok. HELP.

I also have 500 pcs. of the 80 gr. SMK. I would hate to have to sell them.

Thanks

Roy
 
It depends on what velocity you can get with them. If the barrel is long they might stablize. Stability is based upon rotational speed, that is a combination of velocity and twist, the twist can go down if the velocity increases. We experimented with 77grSMK in a 22-250AI at 4000fps in an EPVAT barrel, and had to use a 1-9"twist as they were coming apart with a 1-7"twist.

Since you already have the bullets, try loading a few and shooting them.
 
80's and twist

Roy,

With a 9" twist you "probably" won't stabilize the 80 MK, but it might. A lot will depend on the exact twist of your 1x9" barrel. Check your messages, I'll help ya out.
 
I'd bet that a 1 in 9 twist wouldn't reliably stabilize 80 gr SMK's. They might stabilize with a really hot load on a hot day, but when it cools down a bit they may go wherever they want. I've got a 1 in 9 twist .223 bolt rifle that will almost stabilize 75 gr Hornady HPBT's.

If there's enough slop in the twist rate of your rifle to get it down to 1 in 8 or faster it might work, but that'd be the sheerest of luck.

The military uses a 1 in 7 twist for the 62 gr 5.56 load, and that bullet is much shorter than even a 75 gr Hornady.
 
Larry Elliott said:
The military uses a 1 in 7 twist for the 62 gr 5.56 load, and that bullet is much shorter than even a 75 gr Hornady.
Click to expand...
The 62 grain FMJBT used by militaries around the world has a steel penetrator tip on top of the lead core. Since steel is less dense than lead, the bullet ends up being longer than a completely lead cored projectile of the same weight. The 62 grainer will shoot well out of a 1-9" twist barrel. 68 and 69 grain lead cored projectiles will stabilize from a 1-10" twist barrel.

The real reason for the 1-7" twist barrel in US Military 5.56mm rifles? Tracers - which are longer than an all-metal bullet.
 
Bulletman said:
Roy,

With a 9" twist you "probably" won't stabilize the 80 MK, but it might. A lot will depend on the exact twist of your 1x9" barrel. Check your messages, I'll help ya out.
Click to expand...

Yeah, I'm agree with your statement and appreciates your knowledge and awareness of 80 gr. SMK & twist rate.

Hanging Scale
 
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