7mm-08 Ar10 Build Help

[Jimbo1]

Long time lurker here but finally made an account, should've done it a long time ago lol. So I'm building an aero m5 in 7mm-08 and can't decide on barrel profile and gas block size. I've decided to go with an 18" because I want something that's not too unwieldy so I can carry it for hogs but also want to use it to play around and shoot at some steel at 1000+ yards without it stringing shots. Any suggestions? Thanks in advance!

Ps. Also, does rifle length gas usually work OK for an 18" tube? Not sure how much it being 7mm affects that, I know it's an oddball caliber in the ar world

 

[TonyTheTiger]

In my experience stringing is much more a side effect of barrel quality than barrel profile. If you are going to carry this rifle at all I wouldn't go any heavier then .8" to the gas block and .75" ahead of it.
Rifle length will be fine. In fact rifle +1" might be slightly more fine.

 

[Jimbo1]

In my experience stringing is much more a side effect of barrel quality than barrel profile. If you are going to carry this rifle at all I wouldn't go any heavier then .8" to the gas block and .75" ahead of it.
Rifle length will be fine. In fact rifle +1" might be slightly more fine.

I'm looking at a custom McGowan barrel and the guy I talked to there suggested a modified hbar profile. Do they have a pretty good reputation? I know shilen and bartlein are the best but I dont have unlimited budget and McGowan is affordable and offers the options I want.
I guess my main decision is whether to go with a 750 or 875 gas block and how much that would affect things.
Thanks for the response

 

[Jimbo1]

I was also wondering about any non-traditional barrel profiles, one I came across is the Hanson from ballistic advantage...

 

[TonyTheTiger]

I've got two McGowens, they both shoot great. They'll work with you on profiles, I think you can even specify them when you order online. If you get an .875 gas block journal you're gonna end up with a pretty heavy barrel.

 

[GreenCanoe]

When I built my 7mm-08 AR-10 I had X-Caliber build my barrel. Not saying that McGowen is better or worse, but that's what I bought. I ordered a 20" 8 twist heavy contour starting at the receiver with a 1.150, tapering through .950 to a .750 gas block and maintaining that size through to the threads. Rifle length gas system. Shoots pretty good, but believe you me - its heavy! Would be heavy even with 2 inches of barrel cut off the end, too. Hardest part of dealing with the AR-10 build for me was the load development. Since it's no bolt gun, your charge with be effecting more of the mechanics, so your tuning not only for group size and S.D. but to make sure you can cycle reliably, too.

 

[Jimbo1]

When I built my 7mm-08 AR-10 I had X-Caliber build my barrel. Not saying that McGowen is better or worse, but that's what I bought. I ordered a 20" 8 twist heavy contour starting at the receiver with a 1.150, tapering through .950 to a .750 gas block and maintaining that size through to the threads. Rifle length gas system. Shoots pretty good, but believe you me - its heavy! Would be heavy even with 2 inches of barrel cut off the end, too. Hardest part of dealing with the AR-10 build for me was the load development. Since it's no bolt gun, your charge with be effecting more of the mechanics, so your tuning not only for group size and S.D. but to make sure you can cycle reliably, too.

Interesting, good to see someone else who's built this caliber. I think it's the ideal bullet diameter for the 308 case, pretty close ballistically to 6.5 but with more punch.
That's a fast twist what bullets are you running? Saw the 180gr eld-m that needs like 8.5" twist but wasn't sure if 180gr in a 7mm-08 is even worth it. Great bc though. I'm very curious what loads you're running.

 

[GreenCanoe]

160 gr. Sierra TMKs. I load them pretty hot - CCI BR-2's lighting 44.5 gr. of H4350 gets me to a MV of 2,698 and reliable cycling. This is a compressed load, so be very careful and work up if you decide to try it. But I stay supersonic through 1,400 yards, so that's good...

 

[Jimbo1]

When I built my 7mm-08 AR-10 I had X-Caliber build my barrel. Not saying that McGowen is better or worse, but that's what I bought. I ordered a 20" 8 twist heavy contour starting at the receiver with a 1.150, tapering through .950 to a .750 gas block and maintaining that size through to the threads. Rifle length gas system. Shoots pretty good, but believe you me - its heavy! Would be heavy even with 2 inches of barrel cut off the end, too. Hardest part of dealing with the AR-10 build for me was the load development. Since it's no bolt gun, your charge with be effecting more of the mechanics, so your tuning not only for group size and S.D. but to make sure you can cycle reliably, too.

Interesting, good to see someone else who's built this caliber. I think it's the ideal bullet diameter for the 308 case, pretty close ballistically to 6.5 but with more punch.That's a fast twist what bullets are you running? Saw the 180gr eld-m that needs like 8.5" twist but wasn't sure if 180gr in a 7mm-08 is even worth it. Great bc though. I'm very curious what loads you're running.

160 gr. Sierra TMKs. I load them pretty hot - CCI BR-2's lighting 44.5 gr. of H4350 gets me to a MV of 2,698 and reliable cycling. This is a compressed load, so be very careful and work up if you decide to try it. But I stay supersonic through 1,400 yards, so that's good...

Very cool, have you ever tried a 180gr? You definitely have plenty of twist for it... I know it's kind of pushing the envelope for the size of this case but my math says roughly 1600 yards supersonic, albeit with a lot of drop but damn good bucking the wind

 

[GreenCanoe]

It's something to consider, but I've found that the bigger the bullet you stuff in the case the less you get out of it. Don't forget that in an AR-10 you're limited to a max COAL of 2.80x, being as that's the longest you'll be able to feed out of a magazine reliably. Any additional bullet mass gets stuffed in the brass, reducing case capacity, then you're back to the balancing act of trying to get decent velocity with a slower powder to avoid pressure spikes, but enough gas expansion to cycle a BCG that weighs as much as a suburban. Not saying it isn't worth the effort in development, but I'll at least burn through the 160's I have stockpiled up first.

 

[Jimbo1]

It's something to consider, but I've found that the bigger the bullet you stuff in the case the less you get out of it. Don't forget that in an AR-10 you're limited to a max COAL of 2.80x, being as that's the longest you'll be able to feed out of a magazine reliably. Any additional bullet mass gets stuffed in the brass, reducing case capacity, then you're back to the balancing act of trying to get decent velocity with a slower powder to avoid pressure spikes, but enough gas expansion to cycle a BCG that weighs as much as a suburban. Not saying it isn't worth the effort in development, but I'll at least burn through the 160's I have stockpiled up first.

For sure, a lot of factors. Here's the Hornady data I was going off of and by my math it miiiight keep me supersonic past 1600 although there's a crap ton of drop. It just seems like very few people have even tried messing with 180s in 7mm-08.
By the way I ordered my barrel last night, pretty excited (other than the 3-4 month lead time)

 

[GreenCanoe]

Without knowing your environmental conditions, its difficult to confirm, but it may be possible this summer when you get the barrel. I ran the numbers through 4DOF (see attached) using current weather in A place in MO where I used to live and based solely on that your 1,600 number is a bit optimistic. Currently you'll enter transonic around 1,050ft. That's assuming you get the full 2500fps MV, out of a 8.5 twist with no wind. Again, that's all assuming you have the same environmentals that I used. It could be way better.

 

[troupe]

Wilson sells a 7mm-08 barrel, Wilson with the 1911 fame. I don't know who's barrels they use, but I have not heard any bad with them and the prices are good.

 

[GreenCanoe]

Wilson sells a 7mm-08 barrel, Wilson with the 1911 fame. I don't know who's barrels they use, but I have not heard any bad with them and the prices are good.

After I built my 7mm, a friend wanted one but I convinced him to build a .308. One day a couple weeks later he showed up with a box full of parts and we started to build his AR-10 in .308 with a Wilson Combat barrel. It shoots fine - we would have gotten more done with his load development, but the COVID hit. Unfortunately his timing was less than ideal and since he was just getting started, didn't have a stockpile of primers, bullets and powder so he's waiting for it all to come back to market before he burns the rest of his ammo. I can't blame him, but now my new shooting buddy can't shoot.

 

[GreenCanoe]

For sure, a lot of factors. Here's the Hornady data I was going off of and by my math it miiiight keep me supersonic past 1600 although there's a crap ton of drop. It just seems like very few people have even tried messing with 180s in 7mm-08.
By the way I ordered my barrel last night, pretty excited (other than the 3-4 month lead time)

I'm interested to hear how your build goes, keep us posted!

 

[Phil McGrath]

Hmmmmm, I’ve got two Obermyer heavy barrels that need finished turned. One is a 1/8 the other is a 1/9 rot they are contoured for a M1A/M14, who are you going too use for a reamer?

I was looking at the 171 Match Burner’s 645bc and a oal of 2.90ish for the slow prone.

 

[TonyTheTiger]

When I built my 7mm-08 AR-10 I had X-Caliber build my barrel. Not saying that McGowen is better or worse, but that's what I bought.

I've got two McGowen's and two X-Calibers, I'd put them in the same league.

 

[Jimbo1]

Without knowing your environmental conditions, its difficult to confirm, but it may be possible this summer when you get the barrel. I ran the numbers through 4DOF (see attached) using current weather in A place in MO where I used to live and based solely on that your 1,600 number is a bit optimistic. Currently you'll enter transonic around 1,050ft. That's assuming you get the full 2500fps MV, out of a 8.5 twist with no wind. Again, that's all assuming you have the same environmentals that I used. It could be way better.

Interesting, I'd be interested to see the data from the load you're running. I ordered the barrel by the way but it's like a 3 month production time but I'll definitely post back here when I get it done and take it out. Ordered most of the other parts I needed yesterday straight from aero they had a huge new years sale, so I'll be ready to go when I get the barrel in.

 

[Jimbo1]

Wilson sells a 7mm-08 barrel, Wilson with the 1911 fame. I don't know who's barrels they use, but I have not heard any bad with them and the prices are good.

Yep I saw that barrel but I wanted the faster twist. Would've been a good option though, very well priced.

 

[GreenCanoe]

Ask and ye shall receive.

 

[Jimbo1]

Ask and ye shall receive.
View attachment 7776051

Damn very impressive out of such a short barrel. Now I know why you convinced your buddy to build a 308, so you could kick his ass past 1000 yards
Your numbers look like about a 50% increase over any 308 load I've seen out of that barrel length correct me if I'm wrong

 

[GreenCanoe]

Even the .308's up here do alright. High altitude shooting spoils you, that's for sure, I convinced him that a .308 is a good place to start because there's just less shit to have to develop on your own, since it's the ol "gold standard." i.e. How you read and correct for wind is all based off old .308 data. What most people consider an "effective range" is based loosely off the capabilities of a .308. If you want to learn to reload, there's 7 billion known-good loads for every barrel length, powder type and bullet weight out there on the forums. If you want to find components EVERYONE has a surplus of old .308 brass, and EVERY manufacturer makes a good contender in the .308 caliber. .308 doesn't punish the shoulder but it teaches you how to read wind, calculate for drop (a lot of drop) and it makes you appreciate moving to a 7mm or a 6.5 later. The 308 may be outdated, but its not dead - not by a long shot.

But mostly, I did it so I can tell his holes from mine because mine are smaller. lol

 

[Jimbo1]

Even the .308's up here do alright. High altitude shooting spoils you, that's for sure, I convinced him that a .308 is a good place to start because there's just less shit to have to develop on your own, since it's the ol "gold standard." i.e. How you read and correct for wind is all based off old .308 data. What most people consider an "effective range" is based loosely off the capabilities of a .308. If you want to learn to reload, there's 7 billion known-good loads for every barrel length, powder type and bullet weight out there on the forums. If you want to find components EVERYONE has a surplus of old .308 brass, and EVERY manufacturer makes a good contender in the .308 caliber. .308 doesn't punish the shoulder but it teaches you how to read wind, calculate for drop (a lot of drop) and it makes you appreciate moving to a 7mm or a 6.5 later. The 308 may be outdated, but its not dead - not by a long shot.

But mostly, I did it so I can tell his holes from mine because mine are smaller. lol

Yeah that's what I've gathered, 308 is great for learning how to read wind, drop, etc. So basically because it sucks ballistically
And there's definitely an advantage to using such a ubiquitous cartridge. I might have to build a 2nd upper in 308. Plus it'd be cool to have a semi auto rifle I could load and shoot the old black tip ap bullets out of in case I ever wanted to shoot through an engine block or something like that

 

[B Man]

For sure, a lot of factors. Here's the Hornady data I was going off of and by my math it miiiight keep me supersonic past 1600 although there's a crap ton of drop. It just seems like very few people have even tried messing with 180s in 7mm-08.
By the way I ordered my barrel last night, pretty excited (other than the 3-4 month lead time)

View attachment 7774062

OP, did you ever get your barrel in and how did this turn out for you?

 

[mi650]

Well, Hell! Since I just posted this in another thread...

 

[Coffee_and_Pipes]

Well, Hell! Since I just posted this in another thread...

Nice! How does it shoot?

 

[mi650]

Nice! How does it shoot?

On 1 of my good days, 3/4 MOA. It was very jumpy, though. When it settled down after a shot, it was 4-5' off target at 100 yards.

A guy offered me more money than I could turn down, so I sold it.

 

[EBB]

Long time lurker here but finally made an account, should've done it a long time ago lol. So I'm building an aero m5 in 7mm-08 and can't decide on barrel profile and gas block size. I've decided to go with an 18" because I want something that's not too unwieldy so I can carry it for hogs but also want to use it to play around and shoot at some steel at 1000+ yards without it stringing shots. Any suggestions? Thanks in advance!

Ps. Also, does rifle length gas usually work OK for an 18" tube? Not sure how much it being 7mm affects that, I know it's an oddball caliber in the ar world

Gotta be the heaviest you can carry. for target i have a dpms gen 1 and a real one. it was subminute from the factory with 24" full bull barrel, but once setup and loaded its a 19lb gun. they did have them in 20"too, but thing is anthing not on the heavy side burns up in 10 shots, then has to cool an hour. you haven't seen stupidity than a clown that spent $14000 on an AI 6.5 and decided to havae a truly superior sniper rifle it needed some insane 2400 dollar carbon barrel, and he got six shot out of it, 3 wasted at only 300 yards.
pop for a 20" heavy, a lightweight carbine stock, and it will work. DPMS is back in the act taken over by PSA, they have the site back up although not sure if it will retain its eccentric designs, or lose its name into a budget PSA derivaive.

 

[msgriff]

Gotta be the heaviest you can carry. for target i have a dpms gen 1 and a real one. it was subminute from the factory with 24" full bull barrel, but once setup and loaded its a 19lb gun. they did have them in 20"too, but thing is anthing not on the heavy side burns up in 10 shots, then has to cool an hour. you haven't seen stupidity than a clown that spent $14000 on an AI 6.5 and decided to havae a truly superior sniper rifle it needed some insane 2400 dollar carbon barrel, and he got six shot out of it, 3 wasted at only 300 yards.
pop for a 20" heavy, a lightweight carbine stock, and it will work. DPMS is back in the act taken over by PSA, they have the site back up although not sure if it will retain its eccentric designs, or lose its name into a budget PSA derivaive.

That rifle sure looks familiar. It's the same one posted by ebbiv/Paradox in post #13 of this thread about 9 months ago. Did you open up a new account?
Large Frame Rifle Weights