.308's seem...well...problematical...

[harrylug]

I have a new Aero Precision upper in .308 with an 18" barrel, and this coming week I'll have my new Aero Precision .308 lower in hand. Both pieces "assembled" at Aero Precision. I have a half-dozen of the "proper" 10-round PMAGS on hand, and a few hundred rounds of quality factory ammo in 168 and 175 grain varieties. I don't plan to suppress the barrel...and it has whatever gas block and buffer A-P put on it. My concern is that I am reading here and elsewhere and seeing on YouTube a plethora of articles and videos of folks having serious issues with their .308's...feeding, failure to fire, bad ejections, failure of the bolt to lock back on an empty mag...and more. A lot more of these problems than I see with .223/5/56 ARs.  The .308 platform seems a lot more problematical than the smaller caliber platform... True? Not True? Possibly? What?

[98Z5V]

The very biggest issues are receiver extensions that aren't at the internal depth that they need to be, recoil systems that are out of whack, and gas ports that are too small. 

Edited November 4, 2018 by 98Z5V

[jtallen83]

42 minutes ago, harrylug said:

True? Not True? Possibly? What?

Shoot the schit out of it and find out if it is true for your rifle. Plenty of lube, maybe expect a few malfunction at first until the parts mate. Start with one round in the magazine at a time and make sure it locks back. Doubt you have issues with the Aero stuff but you never know. 

[98Z5V]

The gas port diameter in the barrel is gonna be good to go - It's a Ballistic Advantage barrel.  The recoil system is a little weak, with a 3.8oz shorty buffer, a spring that is barely up to the task,  and measure the internal depth of your receiver extension (this is all advice based on the Carbine recoil system for a collapsible stock setup).  When Aero first started making these receiver extensions, then had an internal depth of 7.100", when it should have been 7.000".  I had some freakish operational issues with one of them, until I found that out.  With a weak(er) recoil system, the rifle will recoil harder, making it seem like it's over-gassed - when it's not over-gassed.

[edgecrusher]

Biggest difference between the two is if you cheep out on a 5.56 it’s not a big deal, the have a mil spec to follow in manufacturing. If you cheap out on a large frame, your getting a pile of shit that may or may not jive. There is no one spec manufacturers follow. Each has their own idea on what they think should be. 

 

Yes, many suckers will slap a half ass rifle together and want a LaRue. No they won’t even come close. There are plenty of proven parts and systems that work. AERO stuff is pretty good with the exception of what 98Z5B highlighted. It’s not that hard to get fixed and you’ll be glad you did.

[harrylug]

What specific buffer and spring do you fellas recommend in case mine are problematical?

[jtallen83]

14 minutes ago, harrylug said:

What specific buffer and spring do you fellas recommend in case mine are problematical?

This kit right here is solid and proven over time to do what needs done.

https://www.armalite.com/product/ar10rekit01-6-position-receiver-extension-kit/

[blue109]

The AR15 has a blueprint. You can download some specs, plug them into a machine, and turn out a bolt carrier that will work in any correctly machined AR15 on the planet. The 308 has no such blueprint, and every manufacturer wants to be the next best thing by changing something on their platform. Most builds will run flawless from day one if you do your research and get the parts that are known to cooperate.  

[Armed Eye Doc]

As has been said, lube it well shoot it first to see if you are going to have problems.  If it is all AP, you will have a better chance of it working together.   If not, it can be diagnosed. 

[JF89]

4 hours ago, edgecrusher said:

Biggest difference between the two is if you cheep out on a 5.56 it’s not a big deal, the have a mil spec to follow in manufacturing. If you cheap out on a large frame, your getting a pile of poop that may or may not jive. There is no one spec manufacturers follow. Each has their own idea on what they think should be. 

 

Yes, many suckers will slap a half ass rifle together and want a LaRue. No they won’t even come close. There are plenty of proven parts and systems that work. AERO stuff is pretty good with the exception of what 98Z5B highlighted. It’s not that hard to get fixed and you’ll be glad you did.

This is true to a point, used to be commercial parts were more common though and those guns usually had all types of stupid issues. I learned that lesson with DPMS and Bushmaster. AR10s are weird, I could not even swap mags between my Armalite and DPMS. That was over 10 years ago though.

[harrylug]

I'm hoping to avoid these problems by buying a  current production Aero Precision upper and lower, along with an Aero Precision BCG. We shall see.

[98Z5V]

It's all high quality parts, so it's gonna shoot.  Before you ever fire it, measure the internal depth of that receiver extension (buffer and spring removed). It should come up to exactly 7.000" internal depth. If it's longer than that, stack quarters down the tube first, to take up that extra internal depth, then reinstall buffer and spring.  Each quarter is 0.069" thick.  What you don't want happening is the BCG slamming into the ears of the lower receiver, just because of a depth that's too much. 

[FrontierOutpost]

On 11/4/2018 at 11:50 AM, blue109 said:

The AR15 has a blueprint. You can download some specs, plug them into a machine, and turn out a bolt carrier that will work in any correctly machined AR15 on the planet. The 308 has no such blueprint, and every manufacturer wants to be the next best thing by changing something on their platform. Most builds will run flawless from day one if you do your research and get the parts that are known to cooperate.  

Do you know of some good info sources for compatible components for the .308? I have a Mega Arms lower and upper and a Nordic lower and upper to build with and want to make both quality machines.

[jtallen83]

22 minutes ago, FrontierOutpost said:

Do you know of some good info sources for compatible components for the .308? 

You are at THE best source for 308AR information. Learn how the search function works here and I bet you can find what you need, if not someone can answer.

It would be difficult for someone to put together an all inclusive list like you want, too many possible combinations.

[FrontierOutpost]

Good point, I am on it. Thanks for the advice.

 

[98Z5V]

FO...  When you search, if you're hunting for something very specific, use the "quotation marks" around it.  If you were to just search on 308 AR BCG for example, everything that includes "308" and "AR" and "BCG" will turn up.  If you search on "308 AR BCG" - you'll get hits that include those three things together...  

[blue109]

This place has a ton of knowledge,  but we are always learning. There are so many new players building receivers that it takes guinea pigs to be sure. We have a few MA10 owners who post regularly and should be able to steer you straight on that one, but you may have just signed up to be our Nordic Components test subject.  Good job!

[98Z5V]

Here is current recoil system discussion:

 

Here is gas system discussion:

 

You solve that, and you'll only have 99 problems - but your Big AR function won't be one of them.

Recoil System first, because it's SO FUCKED, on this platform.  Gas system problems second. In that, gas tube length is primary these days, and gas port diameter is secondary.  Gas systems on this Big AR platform are fucked, too. 

Here's more recoil system information, that's recent:

 

 

When comparing recoil systems, for Carbine Receiver Extensions ("collapsible stocks"), there are two buffers that can be used, but the systems cannot be interchanged.  You go ONE WAY, or you go THE OTHER WAY.  Here's the data on the short carbine buffers:

 

You solve those problems - that manufacturers cannot possibly grasp - and your gun will run.