??
It shouldn't be travelling that far back period, into the receiver or RE. Overgassed or not. If it's that overgassed I would expect the plastic pad at the end of the buffer to be squashed flat, and starting to punch out the rear of the stock!

The fact that it is tells me either the buffer used was too short, or the plastic padded end was removed, or the bolt carrier is shorter than it should be...seriously - open the rifle up; remove the bolt carrier group, and manually shove it into the receiver extension like it would be under recoil. If you can shove it in far enough to touch the receiver or extension, there's a problem. If you want to make it easier, you can pop the action spring out before dropping the buffer back in and trying it...

I spent months researching building my own 308 gasser, between here, 308ar, the hide, and a few other places...the only times this ever cropped up were with wrong bolt carrier groups, or wrong buffers in wrong sized receiver extension. It's possible Aero packaged the wrong buffer with it? Edit - or sent a bad BCG?

Try contacting Aero with this...maybe they let out a bad batch of bolt carrier groups?

FWIW I am using an Aero lower, a Rubber City Armory BCG, a rifle receiver extension with a Brownells 308 rifle buffer and an Aero action spring; I can't make my BCG touch the rear of the receiver or receiver extension with or without the action spring installed. The buffer always bottoms out on the back of the tube before the bolt carrier gets anywhere near the receiver.

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@Evil_Ed

Here it is manually shoved back as far as it can go.
The short 308 sized buffer plastic pad looks perfect no deformation

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@103M95G
I prefer the BCG's with the beveled back of the fat part.  Unfortunately, you discovered why.  I think your pic shows a non-beveled, although the angle could be deceiving.
Suppressed will also make it severely overgassed noshet-out-the-wazoo if you're running a non-adjustable GB.

@Evil_Ed

No spring just the buffer and carrier inside the tube

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kinda tells you how severely overgassed you are, considering that BCG was going back that far and only stopped when it kissed the buffer tube upright, metal on metal.

here's PSA's solution:  pre-divoted.

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Fire formed

or, certificate of lesson learned.  wear that badge-of-honor proudly.  Every time you see it, you'll remember the lesson.  You won't be doing that again, eh?

when the rifle is buttoned up, nobody can see it.  except all your arfcom buddies who see the internet pics.

one of my M5 lowers has those marks, although not as bad as yours.  It must've happened when dialing in a new upper, I had the AGB too wide-open for the first few shots, when trying to dial it in.  Didn't even notice it until weeks later, well, it's a mule, not a show horse.  although FDE cerakoted.

Oof...damn man, dunno what to tell you I honestly never would have thought that a gun could be overgassed that badly to make contact that way, with the correctly sized parts.

This is the BCG I used in my build; even though it says blem...honestly I couldn't find a blem on mine.  If they go out of stock, it'll be back in stock in a week or so. Mine's a factory upper that I replaced the gas block with a Superlative Arms block before I even ever took it to the range...the funny thing is, mine's kind of undergassed Even with the gas block set to wide open/same as an unadjustable block, it struggles to cycle without a can. I think between the 5.3oz buffer weight (weighed it the other day), the 308 rifle spring from Aero, and that the gas block has no carbon sealing around it since it's brand new...it's just leaking until things get situated. I put a borescope down it and verified that the gas block is centered over the gas hole in the barrel, so it's not getting choked out...so I've got the opposite problem that you do

Oh wow it's making contact on the top AND bottom of the receiver extension? I just noticed that, too...maybe the spring they gave you in the kit is the wrong one, too?

Everything seems to be the right stuff, so...yeah, time to buy an adjustable gas block, let all the gas out, and start dialing it back until it barely locks open - then another click or two and call it good

FWIW here's mine:

Holding in the BCG with buffer and spring installed; this is as far as it'll go:



Here it is with no spring in the receiver extension; buffer and BCG only, as far as it'll go:



How it looks from the top, different perspective:



Profile of the RCA carrier:



and last but not least, even though it's visible in a couple of the above pictures, the end of my receiver...no contact, no marks, no dents from the BCG:



Edit - round count on mine is honestly really low, I think it's at 60, all either Lithuanian/GGG surplus, or Aussie/ADI surplus from the early 2000s, when they first started coming in, in the bubble packs and all that.

I am glad I saw this. While I do not have an Aero M5, I have a Stag 10 with 16" BA 308 government profile barrel I assembled. So, it is from the same family of companies as Aero. My rifle was shooting like total trash with ZQI 7.62 ammo. This stuff was shooting around 1MOA for other 308 guns I own, which was awesome for 44 cpr. I use my Hybrid 46 on most of my 30 cal rifles and up and on my Stag, it shoots 2.5-5 MOA groups consistently with the can on an ASR FH. I pulled the can off and shot it with just the ASR FH and shot .5" groups. These were all 3 shot zeroing groups, but still with the can it shot like total shit. I haven't had a gun shoot this poorly with a can on it before. I purposely bought the 16" barrel to run with a can and the BA barrel was on sale for $124. The gas port also had to be drilled out by me because it would not cycle 7.62 without a can and the adjustable gas block fully open.

I'm loving this M5E1 setup so far. All Aero Precision, as it comes from Aero. (16" Aero barrel, Aero gas block, Aero BCG, Aero carbine buffer)
Added a 1-8x Trijicon Credo (34mm/MRAD reticle) in a Badger Condition 1 mount on the range bench. Followed torque specs which Badger conveniently marks on the mount & used my iPhone level. I removed the Aero trigger and dropped in a Larue MBT trigger. I then ditched the included Magpul stock and added a SOPMOD stock.(less wobble)
Assembled the upper receiver to the lower receiver, installed the Aero BCG,lubed properly and proceeded to zero the rifle. First three round group at 25 yards was 2.5" low and 2" right. I moved out to 100 yards for another couple groups, and adjusted, before moving to the steel targets from 200-600 yards. (100 yard groups were about 1.5 to 2.0" off a bag, this rifle is likely more capable, probably me)
The rifles first day out I fired 300 rounds of primarily LC/Win bulk M80 ball. 168gr FGMM performed great out to 600 yards on steel.(In a mountain valley with 10-16 mph wind gusts) The steel antelope/deer lung/heart area at 200 was simple. The coyote steel at 300 was fun. I got several & repeatable 10" gong hits at 300 yards. Quite a few good repeatable hits on an IPSCA sized silhouette at 300,400 & 500. The 600 yard target was a steel buffalo, but I was able to get good hits in the heart lung area.

I am looking forward to get to a local range with steel out to 1000 yards in the near future, just to see what this rifle will do. Ill try some 175 SMKs out there as its on the plains and almost always windy. Overall Im happy with this setup. Not sure its a 1000 yard rifle, but she's impressive at 600, so we shall see where her reasonable limits are. I have not weighed it, and I probably wont. This optic is a beast, seven loaded mags are heavy.... I am OK with that....So is my M1A.

Don't flame me ARFCOM! BUIS, sling and Surefire Warcomp are in the mail!

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Do you mind sharing your recipe?  What barrel, BCG, gas block and buffer system?  Helps the new builders put together a good running 308 AR.

@QtrHorse   Updated in post.

Superlative AGB installed
Opened till 3 o’clock ejection
Installed suppressor  bam! Still smacking the lower.
Closed off the gb till it short strokes, put suppressor on and still hitting the lower brass ejects at 1pm

This is with carbine setup. The rifle system has not been delivered.

I’m wondering if the buffer spring is for 556 and not for 308. Or do they use the same?

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Some of you seem to be running into the same issues as I did, with too short of a buffer. It has to be a .308 buffer, but just as important, is that it has to be the right one for the tube you're running. I found this out the hard way, as well. I'm running a Magpul UBR Gen2 stock, so it's an A5 length tube. I had the bolt carrier strike the rear of the receiver using a 2.5" 308 buffer. After some research, I ordered the Armalite 3.5" carbine buffer from DSG. https://dsgarms.com/lower-receiver-parts-armec0120  Problem solved.

ETA: I used the Armalite 308 rifle spring, but again, that's with the A5 length tube.

@103M95G
I don't think you're going to be able to use one gas setting for both suppressed and un-suppressed.

ETA:
this is the buffer spring I use for my 308, 6.5CM carbine-buffer-tube set-ups:
Slash's HeavyBuffer 308 carbine buffer spring, $15.

308 buffer spring is iirc a stronger spring - but the fact that you got it all from Aero...I mean it's possible they bundled the wrong spring in, but ?

Either way - it's going to be one setting for with a can, and one setting without a can. There MIGHT be a happy medium right in between that works for both, but there also might not be, either.

You could always just buy another spring from Browells or something; they're not that expensive, and see if that "fixes" the problem.

I'm hoping this weekend to get out with mine some more and break it in some...

Also, did you reach out to Aero at all and send this to them? If %100 factory parts are doing this, maybe they have a known issue somewhere and have a fix for it?

I swapped to a Aero 308 rifle buffer system
Adjusted the GB and no longer having an issue, Suppressed or unsuppressed

Thanks everyone for the help
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That looks sweet.

I did this with my m5. I tried different bcg, barrel, gas blocks, and buffers and i couldn't ever get it to cycle reliably.

I removed the carbine buffer tube and installed a 308 rifle tube and buffer and now i can run it suppressed or unsuppressed.

Are you running an adjustable gas block?

I tried several but now with the rifle tube and buffer i just threw a non ajustable block on to see if it ran and it cycled in both configurations. I'm going to put a strike industries adjustable block on it though just to be able to dial it in with and without a can.

So I just inherited a 18” enhanced M5 from my older brother. I don’t think it’s been fired yet, and looks 100% factory parts wise.  He did have a VG6 Gamma set aside for it as well, but other than throwing some glass on it (I'll probably move my Vortex 5-25x56 onto it) I'm not going to fiddle with anything that I don't have to.

Anything I should be on the lookout for?

This project isn't complete yet... but...

.308, Ballistic Advantage 12.5" barrel, 12.7" Aero Precision Altas R-One, Xeno flash hider, Rex Silentium MG7 w/ Xeno mount.

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Putting the M5 to work


Graphic warning


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Does anyone make bolt parts kits for the M5?  I have all my standard AR15 parts and need to start stocking up now that I have a M5.  Additionally is there an agreed on maximum point blank or improved battlesight zero for 308?

Minus some things that’ll get tweaked once I confirm function, I’m pretty much considering my brother’s M5 complete. If it works with the carbine buffer tube, I’ll put a PRS Lite on in place of the well loved Moe fixed. The DIY Daniel Defense grip and cheapo bipod will get swapped as well. The Schmid 2 stage will become a MBT or AST down the road too.

For now it’s plenty good for getting paper or a caribou this fall though.  Wish it wasn’t parts bin stuff, but my brother would be pissed if I put myself in debt fancying up a rifle I can hardly afford to shoot currently.  Getting a caribou with his gun is a good start though.