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Old May 6, 2019, 09:48 AM   #1
disseminator
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Some questions RE 308 AR

Hey all,

I am getting parts together for a 308 AR build and have a few questions for those who have built them. I recently built an AR15 with a Wilson Combat barrel, JP Enhanced Bolt, Superlative Arms Piston, and Geissle Super Recoil Spring/Buffer and I like it very much.

I was looking to do something similar on this AR10. (I am going DI though.)

Parts I have so far include: Wilson Tactical Hunter 18" barrel and the Aero M5 upper/lower receiver set.

I am looking at a few options for the BCG and recoil buffer and that is where my question arises.

I like the JP Enhanced bolt in my 223, so I am going with it again in the 308. They have a "HP" model that features a smaller firing pin hole and includes a smaller firing pin. Any thoughts on this?

Now comes the bolt carrier: is there any sense to using a low mass BCG?

This gun will be for defensive and hunting use and not competitive shooting. I am trying to keep the weight to the minimum but reliability is tops here.

I plan to use an adjustable gas block if that matters.

I will use a Rifle length buffer tube and probably the JP Silent buffer setup with extra springs for tuning.

TLDR: low mass 308 BCG or no?
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Old May 6, 2019, 01:34 PM   #2
riffraff
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Im not a builder, take this for what its worth.

As im sure you know, 308 ARs are less standardized and alot harder to verify fitment with..

Aero M5 handguards, the ones that secure with 8 screws, are really sweet- very solidly and seamlessly on there and simple to remove. Good deals on their upper with handguards, with or without barrels, at optics planet now.

Put > 2000 rounds through an Aero M5 and it was flawless, then started having jams due to overgassing. Fixed via heavy buffer and springco orange, another 1000 rounds now not a single malfunction. Based on that I question if a lighter bcg will help - but with an adjustable block I guess should let you tune it no matter what..

I bet if I had an adjustable block, and I very well may try that some day, I could have run the stock buffer and spring for similar or better results..

As far as a BCG - next one I piece together Im strongly considering the dual ejector toolcraft. The aero bcg works fine but toolcraft has a great reputation, is reportedly compatible, and uses dual ejectors like you find in $3000 versions of these rifles (I assume because there is a benefit in 308 ARs which tend to fail to eject if anything).
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Old May 6, 2019, 05:52 PM   #3
ed308
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I would buy all lower and upper parts from Aero due to possible compatibility problems. Aero makes a BCG with HP bolt. Although with a .308, not sure the HP bolt is necessary. But if 6.5 CM then would recommend. The adjustable GB is a good idea since most AR10s are over gasses.
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Old May 6, 2019, 06:35 PM   #4
stagpanther
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I've built quite a few AR10-style AR's--and as others have mentioned above it generally pays to buy your upper and lower from the same manufacturer. Same holds true for the PK's--once in a while I've seen small variations in the pivot pin holes and sizes which create alignment problems. I've also occasionally seen some slight variations in selector/safety size or position which can create problems in adjusting the trigger group.

Balancing your gas system will in general be harder for an AR10 build than it is for an AR 15 build--at least that's been my experience. The exception to that being a "run of the mill" conventional 308/7.62 x 51 build which tend to be slightly overgassed but usually will successfully fire most loads.

Things start getting trickier with other caliber/cartridges and barrel lengths--at least that's what I found. I probably wouldn't do any AR10 build without an adjustable gas block nowadays. Bigger cartridges also mean faster crud build-up--no matter which route you go with a BCG--I've found an NIB coated group is generally worth the extra investment for increased reliability in an AR 10 build--more so than in an AR 15 build in my experience.

Another thing--these things tend to be heavy, especially once you put a scope on, so some thought beforehand on how heavy or light you want it to be will have a big influence on what components you buy. A good muzzle device will also make a significant difference IMO--I did a build using a Wilson 338 fed lightweight unthreaded hunting barrel-- it shoots well but also has significant muzzle flip and hits relatively hard--making it harder to keep on target for follow-up shots. the fluting and logo goes right to almost the muzzle, so I can't really thread it.
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Last edited by stagpanther; May 6, 2019 at 06:45 PM.
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Old May 9, 2019, 02:39 PM   #5
Jsnake711
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I'd say no low mass. It'd be slamming into your shoulder. It also might wear that piston out. My hunting 308 weighs in at 13.4lbs
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Old May 9, 2019, 02:57 PM   #6
stagpanther
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Quote:
My hunting 308 weighs in at 13.4lbs
I'm impressed--that's some hauling. ; )
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Old May 9, 2019, 09:03 PM   #7
disseminator
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Quote:
I'd say no low mass. It'd be slamming into your shoulder. It also might wear that piston out. My hunting 308 weighs in at 13.4lbs
Would a low mass BCG do that even with more spring weight? My motivation is to keep the weight down. I definitely don't want it to weight 13.4 lbs.

I added an Aero M5 lower parts kit and Melonited gas tube to the parts pile today.

Getting closer. I decided on a Magpul PRS for the butt stock, and will likely go with the Aero light weight tube on the front.
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Old May 10, 2019, 07:51 AM   #8
Jsnake711
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Like a tubs wire? possibly not. But it may take a little more tuning. The Adj. Gas block will help.
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Old May 10, 2019, 08:45 AM   #9
ed308
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Surprised you're going with the PRS stock if wanting to keep the weight down. Heavy bulky stock. But I like them for a bench AR. I also have one on my 6.5 CM Savage bolt with a MDT chassis.
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Old May 10, 2019, 11:29 AM   #10
brasscollector
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Carbine extension tube/buffer is going to weigh less than the rifle counterparts. Depending on gas port size and locale you may need (or want) an adj gas block, I don't have an AR10 w/o one. If you went with a low-mass BCG you are almost certain to need some adjustment in your gas system. Since you mentioned reliability I would just go with a standard mass BCG and save as much weight as I could elsewhere.
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Old May 10, 2019, 08:29 PM   #11
riffraff
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Quote:
Originally Posted by disseminator View Post
Would a low mass BCG do that even with more spring weight? My motivation is to keep the weight down. I definitely don't want it to weight 13.4 lbs.

I added an Aero M5 lower parts kit and Melonited gas tube to the parts pile today.

Getting closer. I decided on a Magpul PRS for the butt stock, and will likely go with the Aero light weight tube on the front.
As far as the aero handguard, if thats what you mean by tube - Ive got both the Atlas and Enhanced in the AR15s but I found for general purpose I prefer the wider bolt-on Enhanced (with a few extra ounce) versus the narrow clamp on Atlas.. for that reason my M5s are the Enhanced version not the Atlas...

Basically its nice to have 8 screws positively securing the guard but also those thin ones feel chincy to me and put your hand closer to a hot barrel.

For weight savings, you are not buying much with an 18 versus 16 inch barrel and its really the weight out in front that hurts the worst - just something to consider.
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Old May 10, 2019, 11:08 PM   #12
disseminator
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Quote:
Surprised you're going with the PRS stock if wanting to keep the weight down. Heavy bulky stock.
Your totally right on this, I'll look some more.....

Quote:
Carbine extension tube/buffer is going to weigh less than the rifle counterparts. Depending on gas port size and locale you may need (or want) an adj gas block, I don't have an AR10 w/o one. If you went with a low-mass BCG you are almost certain to need some adjustment in your gas system. Since you mentioned reliability I would just go with a standard mass BCG and save as much weight as I could elsewhere.
You are likely right about the BCG being a potential source of pain with a low mass setup. I'll take your advice and get a regular BCG. I think I'll get the JP BCG with HP bolt and the silent recoil spring.

Quote:
As far as the aero handguard, if thats what you mean by tube - Ive got both the Atlas and Enhanced...
Yes, I meant the hand guard. I'm leaning towards this one, I have the standard, non enhanced upper:

https://www.aeroprecisionusa.com/m5-...-lok-handguard

Black, 15". The shorter one is only a few ounces less and I really prefer a 15", all my AR rifles have them.

Thanks for the help guys, keep it coming.

Still need to decide on a trigger and a muzzle device. I was next to a guy at the range the other day and he was shooting a SCAR with a brake/break and it was obnoxious so a flash hider is where I'm leaning.

Anyone have an experience with this one: https://www.noveske.com/products/kx5...w-crush-washer

D.
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Old May 11, 2019, 07:38 AM   #13
bfoosh006
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Consider an A2 stock if you really want a rifle length stock, they really are a decent design.

As for the Low mass BCG, I would tend to think, and while it might work, you want the mass of the regular BCG to help feed and function, and leave the bolt locked slightly longer ( from the additional mass ) .. that results in extraction at a lower chamber pressure. ( Easier extraction )

A heavy buffer weight will also aid in delaying the bolt unlocking. Even just a few milli-seconds matter.

And I use Lantac brakes and BCM ... the Lantac will be more annoying to those around you..for sure because of the angle of the ports.. ( any brake will the ports angled towards you will be worse )

But the BCM 308 is pretty manageable.
You might consider one of those.
https://www.bravocompanyusa.com/BCMG...-mod-1-762.htm

Make sure which ever free float tube you buy .. will allow ample clearance around the Adj. GB.

And IMHO, a adj. GB is the best add-on for any large frame AR. Buy a quality one.. the cheaper , less user friendly ones can be a PITA to adjust.. especially if the adjustment screws are not readily accessible.

I have been very happy with my SLR's.. and they go on sale frequently.

Trigger wise... the LaRue MBT 2 stage is a heck of a deal. I prefer 2 stage triggers... they are much easier to back out of a shot then a single stage.
The LaRue comes with a flat ( or curved ) trigger bow now.

Remember to do some QC on the various new parts... polish the feed ramps and RE feed lugs edges, polish the extractor face ( the portion that slips over the cartridge rim )

And a snug upper to lower fit makes it easier for you to have a consistent firing stance.

And if you want to get as much accuracy as possible from the barrel... consider lapping the upper receiver face true. $30 tool, and for me, doing this has helped precision on all the rifles I have built.
FWIW, it helps with full , complete, contact between the barrels bridge / barrel nut / upper receiver face.
IMHO, it is important. At the very least it will shoot more brand ammo's in tighter groups.
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Old May 11, 2019, 11:53 PM   #14
riffraff
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Im not sure I get the whole muzzle break thing. A standard birdcage leaves nothing desired for me. At least in .308 they just dont kick that bad, maybe in something exotic there's a good reason but Id try a standard flash hider first.
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Old May 12, 2019, 09:50 AM   #15
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If muzzle blast is a concern, I’d look into a linear compensator. Kaw Valley is what I prefer, but it made a big difference, to the shooter and bystanders, on my HK G3K clone. It directs all the gas and blast forward away from the shooting line.

Muzzle brakes have their purpose, but I only have them on target rifles or pig hunting rifles. None of my deer hunting rifles have a brake. Even my 6.5 Creedmoor has a break and it recoils less than a .308. It’s not only to reduce recoil, the right brake reduces muzzle rise so it’s easier to get back onto or stay on target for follow-up shots. Makes a big difference when hunting feral pigs so you can take out 3-4 before they scatter instead of just 1.
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