AR10 build in 7mm-08

[Jm32526]

Ok.... I am building a 7mm-08 on a mega maten matched upper/lower. I ordered my barrel a while ago, but I wanted to run something by the masses..so here it goes...... I ordered a Krieger barrel finished to 22". I was debating between 1-9" or 1-10". The person at Krieger said, "why don't you just do 1-9 1/2"? So that is my question to you, why don't I just do 1-9 1/2"? I plan on mostly target shooting with a possible deer hunt here and there. I would like to use high BC bullets, but of course magazine fed weapons have there limitations. Any thoughts on the matter or should I just take it and run with it? I reload so I will do a thought of testing before I commit to one load, but any advice you want to throw at me for that would be great also. Thank you for reading this!

 

[mic2377]

I struggled with the similar dilemmas regarding a 7mm-08, and ending up building a 1-8.5 twist 6.5 Creedmoor. It just fits better in the 308 AR platform IMO, and requires no compromises in terms of seating depth even with the high BC 140 gr bullets.

I don't think the twist rate will be a big issue since the 7-08 doesn't really have the horsepower or OAL room in a semi-auto to utilize the 180 class VLD bullets anyways.

I am curious to hear other opinions on both the twist rate and 7-08 in semi autos.

 

[jonbearman]

Go with 1 in 9 minimum as you are marginal at 1 in 9.5. And like mic 2377 a 1in8.5 would be better in my opinion.

 

[jamesh]

I would go with the 9 twist or as mic suggested go with a 6.5 Creedmoor. I have had excellent luck with my AR in 6.5 Creedmoor and 8.5 twist. I only shoot 140 Amax in it.

 

[flatlander]

I bought a Krieger DPMS-contoured 7mm/1-10tw bbl a few years ago to use in an AR-10 build in 7-08 Imp 30*. Only reason with went with the 1-10tw was because it was immediately available. Dunno whether it's the slower twist, or whether I just haven't found the right combination of components yet, but out of all the loads I've tried with Sierra 130, 150, & 168gr MKs, only the 130s have produced consistently pleasing groups, whether at 100 or 600yds.

I figured 1-10 would be plenty fast enough for S168MKs, and also figured that'd be the heaviest bullet I'd want to use in magazine fed ammo. Have to admit though, my motivation for continued testing with this rifle has been a little lacking, what with the disappointing accuracy & velocity out of the 168s. Also, the tightness of supply of components has made it even harder to justify shooting out of my limited stock of components. If I had no other projects to deal with, and an unlimited supply of components, I might get off my butt and work at this a little more.

But as far as your choice of twists go, if you decide to go with the 7-08, I'd recommend ordering a 1-9tw blank - it's a proven twist (I've got four 1-9s on 284s & 280AIs, and they're all I could ask for in the accuracy dept.), and that's one less thing to worry about.

 

[Jm32526]

Great input. It seems like the majority of people and research I have done prefer 1-9 over 1-10. I wish I had more knowledge on all this stuff. I have only been reloading for a couple of years, so I have a lot of catching up to do. Thank you all for your advice!!

 

[gunsandgunsmithing]

Ar's shoot great for a semi-auto...really, they do, but they aren't bolt action dedicated benchrest rifles. The difference in twist will be lost in the noise of the platform on which it's built. IOW, it won't matter. Use the twist that will stabilize the heaviest, er, longest bullet you foresee using.


I'm not dissing AR's..they just have their limitations. Seeing the accuracy difference of two different twists is within the limitations of the whole platform. IME, the AGGING ability of an AR with the best of everything is in the 3's. Not that they won't shoot the occasional wallet group, but I'm strictly talking all day, every day groups. That ain't no slouch, but it's not going to improve with twist rate, IMHO.--Mike

 

[Jm32526]

Well it has been a year in the making. I finally got my rifle finished. Here is a list of components:

Mega Maten matched upper and lower
Kreiger Barrel 22", fluted, 9.5 twist, .90 at the muzzle, chambered in 7mm-08
Superior Weapon systems 13.9" handguard
Syrac adjustable gas block
Timney trigger 3.5lb
JP enterprises bolt and one piece recoil spring
Leupold Mark IV 8.5-25 50mm
Nightforce unimount
Magpul PRS stock

I have only got to shoot it a couple of times so far. The load I ended up with for now is 40.5 grains of RL-15, 140gr Berger VLD, 2.800 OAL, Nosler 7mm-08 brass. I haven't got to shoot it passed a 100 yards yet but it has gone well so far. Shot a 3 shot 1/2" group with this load. Thank you all for your suggestions, as I always appreciate it. If anyone happens to have any other load data for 7mm-08 I am always looking for something better

 

[jonbearman]

I would say that gun shoots. Good job my friend!!!!!!!!!!!!

 

[Jm32526]

Thank you Jon!!! It was a little nerve racking at first given I had a fair amount of uncertainties. Felt a lot better after the 50 yard group. Had to make a couple of adjustments with the scope for eye relief, then got zero at 100. Of course I am not out of the woods yet.... My pals and I are going out in the next week or so to do some longer range stuff. I will update my post when I'm done.