AR question.. 1:8 or 1:9 twist

[lilvega]

I know the faster twist allows for heavier bullets but what if any are the real world practical advantages?

I am about to order a dpms setup and the barrel I want is offered in both but 1:9 is in stock while 1:8 is 6-8 weeks. Worth the wait? More accurate across the board?

[mustang_revival]

http://www.thehighroad.org/showthread.php?p=5746898

Interesting discussion here.

[lilvega]

http://www.thehighroad.org/showthread.php?p=5746898

Interesting discussion here.

Yeah, that is pretty much what I have been told.
My dad has a colt h bar heavy match with 1:7 twist and he keeps preaching the fast twist to me. I really don't think it will make any difference for what I will use it for. Plinking, cyotes and pigs.

[mustang_revival]

Yeah you will probley experience noticeable differences more based on ammo type vs. barrel twist.

[CJ]

Yeah, that is pretty much what I have been told.
My dad has a colt h bar heavy match with 1:7 twist and he keeps preaching the fast twist to me. I really don't think it will make any difference for what I will use it for. Plinking, cyotes and pigs.

Faster twists wear out quicker. 1:9 is good up to 62gr and sometimes 69. For 75 you will want a 1:8 if it is a longer barrel, 1:7 if shorter.

[FRider]

I shoot 40gr Sierra HP - 75gr Hornady BTHP at .5-.6in 5 shot groups with 1:9tw DPMS AR.

The 36gr Barnes Varmint grenade got .7in 5 shot group at the tightest. I need to change my powder and COL and may tighten it up some. I have some 77gr SMK I need to load up and shoot. Some guys with 1:9tw barrel say the 77gr SMK works great in their high power matches out to 600 yards.

The 1:8 should shoot the 75gr Hornady BTHP and 77gr SMK or Nosler CC a little tighter with good accuracy with 40gr. This covers almost all factory ammo. These are all mag length loads.

If you don't plan on shooting the 77gr in mag length, or 80gr single fed, then 1:9tw should work great.

[CJ]

I shoot 40gr Sierra HP - 75gr Hornady BTHP at .5-.6in 5 shot groups with 1:9tw DPMS AR.

The 36gr Barnes Varmint grenade got .7in 5 shot group at the tightest. I need to change my powder and COL and may tighten it up some. I have some 77gr SMK I need to load up and shoot. Some guys with 1:9tw barrel say the 77gr SMK works great in their high power matches out to 600 yards.

The 1:8 should shoot the 75gr Hornady BTHP and 77gr SMK or Nosler CC a little tighter with good accuracy with 40gr. This covers almost all factory ammo. These are all mag length loads.

If you don't plan on shooting the 77gr in mag length, or 80gr single fed, then 1:9tw should work great.

Pretty good grouping with 75gr, what length barrel are you shooting out of? That is the absolute limitation of a 1:9. Not bad, but at 600 yards no damn way. Last time I was shooting long range the only semi auto guys that even came close to qualifying were all using 1:8 24" barrels. the 1:9 barrels fall off after 200-300 yards or so. I've seen several 1:9 keyhole 75gr's at even 100 yards. Some 1:9's can do it, some can't. Either way for long range, none of them are a good choice when it comes to overall consistency, it's the limitation of their twist rate. A lot of this has to do with velocities. Most standard store bought 75gr's may very well keyhole or go bouncing off the dirt because of insufficient velocity. To stabilize heavy bullets in a slow twist rate you have to compensate with velocity, sometimes you can't buy a hot enough load commercially to do that with a 1:9. I suspect your hand loading is probably one of the reasons you're able to group with a 1:9.

[lilvega]

I talked to dpms again and they agreed to build in 3 weeks so I ordered the 1:8 twist.

[Osiris]

Mine is 1:7.

[FRider]

Pretty good grouping with 75gr, what length barrel are you shooting out of? That is the absolute limitation of a 1:9. Not bad, but at 600 yards no damn way. Last time I was shooting long range the only semi auto guys that even came close to qualifying were all using 1:8 24" barrels. the 1:9 barrels fall off after 200-300 yards or so. I've seen several 1:9 keyhole 75gr's at even 100 yards. Some 1:9's can do it, some can't. Either way for long range, none of them are a good choice when it comes to overall consistency, it's the limitation of their twist rate. A lot of this has to do with velocities. Most standard store bought 75gr's may very well keyhole or go bouncing off the dirt because of insufficient velocity. To stabilize heavy bullets in a slow twist rate you have to compensate with velocity, sometimes you can't buy a hot enough load commercially to do that with a 1:9. I suspect your hand loading is probably one of the reasons you're able to group with a 1:9.

I have the DPMS panther bull 20 with 20in 1:9tw chromoly barrel that is not chrome lined. I get 2900fps with 75gr Hornady BTHP, and 3000+fps with 69gr SMK. I use Varget, R15 for the 60+gr bullets and Benchmark or R10x for the light ones. AA2230 can cover the whole gamut, for the most part, of .223.

This is the Hornady 75gr BTHP which is similar to the 77gr SMK. The 75gr Hornady A-Max is a whole 'nother animal. I haven't tried those.

The only factory loads I've used are the Federal 50gr JHP. They were plenty accurate, and killed a button buck at 200 yards.

My most accurate loads are 52gr SMK handloads. I can do 5 and 10 shot groups under 1/2in. Best was a .488in 5 shot group. 3 shot groups are in the .2's and .3's.

I put some bells and whistles on it. Burris PEPR mount with Black Diamond 8-32x, single-feed load block, but the JP Rifles trigger is still sitting in the bag.

There's other tricks like removing the gas tube and twisting the gas block 90 degrees. Of course, you will be single feeding.