Does Aero Precision AR308s do anything different than the others?

[Basic user]

Decided on a collapsible (carbine) stock for this new Aero 6.5 gas gun build and the bolt won't go all the way back to lock open; it's about a quarter inch short. The buffer springs bottoming out and I can not figure out why. I know the whole "there's no single spec for ar308s/ar10s" thing, but finding out what's compatible and what's not seems to be pretty challenging. I keep seeing that the buffer tubes and buffer springs are compatible, but buffers are not. So, then how does this carrier tail bottom out? The tube's Strike Industries, the buffer's an adjustable Expo Arms, and the springs a no name AR15.
So during my research, the only thing I found was that on Aero's website, their 308 carbine spring has a different part number than their AR15 carbine spring... but when shopping on all the ar parts websites, they all list (except for aero) all the same springs for the 308s and 556s...
Called Brownells and they list the OAL's for the springs in their notes, and the 308 springs thicker and longer lol. Would Im imagining would exacerbate my issue (if those measurements are correct) or does the 308 spring have so fewer coils that it maintains a shorter compressed OAL...

Has anyone built one from the ground up on an Aero set and run into this same problem?

 

[jetjock07]

There are two different systems, carbine and rifle configurations. You may have a rifle buffer spring in a carbine buffer tube.

 

[Basic user]

I took it out of my AR15 carbine. Does that make a difference? I'm thinking not.

 

[jetjock07]

Just giving suggestion based on info man.

 

[Basic user]

It has to be this spring... I'm thinking Primary Arms' stuff is wrong lol.

 

[Basic user]

Just giving suggestion based on info man.

No I get it; we have to try everything. I will get this sorted lol.

 

[loclass]

Are you using a standard ar15 buffer in a standard 7" buffer tube? If so you have the wrong buffer. If you're using a 7" carbine buffer tube on an LR308 then you need the "shorty" lr308 length buffer.

 

[bfoosh006]

Are you using a standard ar15 buffer in a standard 7" buffer tube? If so you have the wrong buffer. If you're using a 7" carbine buffer tube on an LR308 then you need the "shorty" lr308 length buffer.

Typically Aero 308 uses a AR15 carbine buffer tube... and that requires a 2.5" buffer be used.

IE, the longer "308" BCG needs extra room to fully compress into it.

Just adding specific OAL buffer length.

 

[Basic user]

I'm using the user adjustable Odin Works 308 buffer. That's correct right?

 

[Darryle]

Here's some fodder for you to read, scroll down and there is a list of measurements for tubes, springs and buffers. I just know that when I built my first large frame AR, I heard the term, "There is ¢.75 difference between Large Frame AR buffer tubes", turns out if you wind up with the longer one, 3 quarters will fix the problem.

Compatibility Large Frame ARs

 

[AMGtuned]

I'm using the user adjustable Odin Works 308 buffer. That's correct right?

Carbine RE on a large frame, requires a "308 carbine" spring and a 2.5" length buffer.

You did not get any of those things by removing them from any ar15. Maybe the tube.

The longer (3.5"?) buffer found in ar15 type rifles, will work in large frame when using an A5 RE.

The last option is a rifle length RE, 308 rifle spring and buffer.

Once you have that part figured out, then you can tackle the rest.

When i built my ar10, I used the rifle system and a prs3. I switched out the Carbine system after trying to fire some 2700fps bolt gun loads that were popping primers out in the ar10. AGB helps a lot, but is not necessary

 

[Basic user]

Carbine RE on a large frame, requires a "308 carbine" spring and a 2.5" length buffer.

You did not get any of those things by removing them from any ar15. Maybe the tube.

The longer (3.5"?) buffer found in ar15 type rifles, will work in large frame when using an A5 RE.

The last option is a rifle length RE, 308 rifle spring and buffer.

Once you have that part figured out, then you can tackle the rest.

When i built my ar10, I used the rifle system and a prs3. I switched out the Carbine system after trying to fire some 2700fps bolt gun loads that were popping primers out in the ar10. AGB helps a lot, but is not necessary

That site is saying there different sizes of buffer tubes for the AR10 and 15; are they grouping the AR308 in with that?

 

[hlee]

I took it out of my AR15 carbine. Does that make a difference? I'm thinking not.

The ar15 carbine buffer is longer than the lr308 buffer. You need a different/shorter buffer.

 

[Darryle]

The ar15 carbine buffer is longer than the lr308 buffer. You need a different/shorter buffer.

He's already too short, remove the spring and follow these instructions to eliminate the spring as the culprit

Buffer/Tube issues

 

[AMGtuned]

That site is saying there different sizes of buffer tubes for the AR10 and 15; are they grouping the AR308 in with that?

Diameter; no, not that I'm aware of.

Length; I'm also quite certain that Carbine is carbine, a5 is a5, and rifle is rifle.

Spring and buffer are different.

Aero Precision themselves sell the carbine "kit" you need. Matter of fact, there's one on my rifle now because I didn't have another rifle system for it. It's a carbine RE, 2.5" h3 buffer, and 308 carbine spring.

 

[msgriff]

Wrong spring.
An M4/AR-15 carbine spring will not work with a 308 short carbine buffer (2.5" OAL) in a M4/AR-15 carbine receiver extension (7" inside depth).

The maximum allowable compressed spring length of a 308 short carbine buffer is around 2.000"-2.125".
An M4/AR-15 carbine spring with 37 coils and a wire diameter of 0.072" is 2.736" long at full compression.
An AR308 carbine spring with 26 coils and a wire diameter of 0.075" is 1.950" long at full compression.

Dimensions listed can vary between manufacturers and allowable variances/tolerances.

 

[Basic user]

He's already too short, remove the spring and follow these instructions to eliminate the spring as the culprit

View attachment 8522618



Buffer/Tube issues

I did just that; that's how I made my guess that the current culprit is the spring. That was my guess anyhow.

 

[mtrmn]

I took it out of my AR15 carbine. Does that make a difference? I'm thinking not.

Yes--that's the problem most likely.
I was cleaning my 308 and when I put it back together I just picked up a spring. It was for an AR15 that I also had tore down. Same problem you stated. Get a 308 carbine spring.

 

[Shooter McGavin]

M5 .308 Carbine Buffer Kit

Shop M5 .308 Carbine Buffer Kit, No Stock and more online at aeroprecisionusa.com. Free shipping on all orders over $99.

www.aeroprecisionusa.com

 

[wade2big]

M5 .308 Carbine Buffer Kit

Shop M5 .308 Carbine Buffer Kit, No Stock and more online at aeroprecisionusa.com. Free shipping on all orders over $99.

www.aeroprecisionusa.com

If he uses that kit he needs to throw that light buffer away and buy this:

https://kakindustry.com/lr-308-carbine-buffer-heavy

He will be mighty unhappy if he picks up a 22” rifle gas 6.5CM upper that Aero sells and will be really disappointed if he pairs it with the Aero buffer kit quoted above while keeping the 3oz buffer.

 

[r.tenorio671]

TBH, if you are using an Aero upper and lower, just purchase the Aero buffer system (tube, buffer and spring) and an Aero BCG and you should be G2G.

FWIW, the Aero .308/6.5CM nitrided bolt claims to be a "HP" bolt, i.e., smaller diameter firing pin and firing pin hole. It is smaller than the typical .308 bolts, but not as small as the JP's....