Help with an abusive rifle?

[bugman]

Good evening gents,

I'm hoping some of you heavy-duty problem solvers out there can help me out with my Aero M5 308 build. Based on info from this forum, I have been able to get the gun running. It will shoot, reliably, and for that I'm grateful. However, my new problem is that it's rough as hell. Kicks like a mule, and consistently ejects 8-10 feet at 1:30 or so. I hate to see what it might do when I try to put a suppressor on the end of it.

In an effort to tame it, I have done some experiments to this rifle (one at a time); therefore it has gone through several "iterations" which I will describe below using the Waterboarding template. In all cases, the gun functioned, but all suffered from the same un-smooth shooting characteristics (heavy recoil and far-forward ejection).

ITERATION #1

1. Armalite AR10 recoil system? NO
2. Buffer weight: 6.5 oz advertised, 6.63 oz measured
3. Buffer length: 2.5" advertised, 2.6195" measured
4. Extension buffer tube internal depth: 6-15/16" measured (Aero)
5. Buffer spring:
   • Brand: HeavyBuffers.com Custom 308 Carbine Spring
   • Length: 11-5/16" measured
   • Coil count: 28 coils
6. Gas system length: Mid-length
7. Gas tube length: 11-3/4" advertised and measured
8. Photo in magwell
9. Photo of bolt face
10. BCG clearance at:
    • Receiver ears: 0.287"
    • Bolt stop: unknown, but adequate
11. Gas
    • Journal diameter: 0.750"
    • Port diameter:
      • #49 drill GOES (but barely) 0.073"
      • #48 drill DOESN'T GO (0.076")
12. Description of problem: heavy recoil and ejection at 1:30. Carrier moving too fast?
13. Additional info:
    • No significant damage to brass (see pics)
    • Using Aero BCG - 18.48 oz assembled weight; "tail" length of 4.6095"
    • Barrel is Criterion M118LR, chrome lined, 16" mid-length gas

ITERATION #2

• Changed bolt carrier to Lantac "Enhanced" Bolt Carrier (using same Aero bolt from Iteration #1).
  • The Lantac Enhanced Carrier is advertised as having "increased mass" and "larger vents" (their words, not mine) presumably to help remedy overgassed condition.
  • However, I thought it was noteworthy that the assembled weight of the Lantac Enhanced BCG was actually less (18.02 oz) than the Aero BCG.
• All other elements from Iteration #1 remained unchanged
• This change yielded NO IMPROVEMENT, and no difference at all, that I could perceive.

ITERATION #3

• Switched back to Aero BCG from Iteration #1
• Refer to Waterboarding Item #5
  • Changed buffer spring to Sprinco Orange:
    • Length: 11-1/4" measured
    • Coil count: 28 coils
  • The spring itself felt a little bit stiffer than the HeavyBuffers.com Custom 308 Carbine Spring
  • This change also yielded NO IMPROVEMENT

ITERATION #4

• Decided to change out the whole recoil system entirely, to get more mass and hopefully a better spring.
• Ordered an A5 tube, 3.25" XH Buffer, and EA-1095 spring from HeavyBuffers.com
• Refer to the following Waterboarding Items that changed:
  • #2 - Buffer weight: 8.5 oz
  • #3 - Buffer length: 3.25"
  • #4 - Extension buffer tube internal depth - 7-5/8" advertised; 7-13/16" measured
• All other elements from Iteration #1 remained unchanged
• NOTE: I did not believe this setup provided the BCG adequate clearance at the receiver ears due to the increased depth of the receiver extension beyond the advertised 7-5/8", or maybe I just have a short bolt carrier. It was only going to clear by less than 0.05", not accounting for compression of the buffer bumper.
• I decided to throw in a couple of quarters to prevent the carrier from smashing my lower receiver, which was effective, if not somewhat inelegant. Be that as it may...
• This change yielded NO IMPROVEMENT

ITERATION #5

• Last ditch effort.
• Replaced EA-1095 spring with Sprinco Orange (11-1/4" length; 28 coils)
• All other elements from previous Iteration (#4) remained unchanged.
• This change also yielded NO IMPROVEMENT

So after all that, the rifle is still beating me up and ejecting at 1:30, I never saw it let up in any noticeable way. You guys have any thoughts? Can I smooth this thing out somehow, or should I just be happy that it runs at all? Here are a few possible solutions I have considered, but I wanted to get some feedback from yall before trying these, or anything else (I'm running short of funds for further experimentation...)

• Stiffer spring for A5 system? I have seen the Stag Arms buffer spring mentioned specifically. Would that be a possibility? Or something else?
• Since I already have the heaviest A5 buffer I can find, should I consider changing the recoil system (again) to a rifle system? That way maybe I could get up to a 10 oz buffer, and possibly have some additional spring options.

The only thing I'm sure I would NOT want to try is an adjustable gas block. My experience with those has not been positive.

Greatly appreciate any words of wisdom.

[shooterrex]

Good effective muzzle brake.

[bugman]

12 minutes ago, shooterrex said:

Good effective muzzle brake.

I'm using a brake, but I'm not sure how effective it is. It's the 4-port brake that goes with the OSS flow-through style can. I'm afraid my options are limited for muzzle devices.

[98Z5V]

2 hours ago, bugman said:

• Ordered an A5 tube, 3.25" XH Buffer, and EA-1095 spring from HeavyBuffers.com
• Since I already have the heaviest A5 buffer I can find, should I consider changing the recoil system (again) to a rifle system? That way maybe I could get up to a 10 oz buffer, and possibly have some additional spring options.

 

2 things I noticed here.    You don't have a VLTOR A5 receiver extension, because you stated it's longer than the advertised 7 5/8".  VLTOR does NOT mess this measurement up, ever.  VLTOR supplies these things, under contract, to the US Marine Corps.  They never make this mistake, and machine them deep.

So, one of two things is going on here. #1.  You don't have a VLTOR product, but you're calling it "A5 tube."  #2.  The 7 5/8" measurement is an internal depth measurement, not an OAL measurement.  You might be measuring it incorrectly, here.

Okay, I said 2 things, and that was Thing 1.  Here's Thing 2.  You better not be running a VLTOR A5 buffer in a .308AR.  That buffer will be too long.  I know you gave a dimension, a length measurement, but then you also stated you're running the heaviest A5 buffer you could find.  The heaviest A5 buffer is the 6.83oz A5H4 buffer.  I know because I've got one in a 6 ARC gun right now. A5 buffers are 4.000" long, and they're only used in Small Frame ARs.  Never used in Large Frame ARs.

So, some clarification on those parts will be necessary.

You stated it's abusing you.  What's your history with shooting .308 Win? 

Everything else in your numbers look decent, and your parts list doesn't suck.  Your gas port is a touch smaller than I would recommend, for your barrel configuration - but it's working, and throwing brass at 1:30. 

Edited February 28, 2023 by 98Z5V

[bugman]

17 minutes ago, 98Z5V said:

2 things I noticed here.    You don't have a VLTOR A5 receiver extension, because you stated it's longer than the advertised 7 5/8".  VLTOR does NOT mess this measurement up, ever.  VLTOR supplies these things, under contract, to the US Marine Corps.  They never make this mistake, and machine them deep.

So, one of two things is going on here. #1.  You don't have a VLTOR product, but you're calling it "A5 tube."  #2.  The 7 5/8" measurement is an internal depth measurement, not an OAL measurement.  You might be measuring it incorrectly, here.

Okay, I said 2 things, and that was Thing 1.  Here's Thing 2.  You better not be running a VLTOR A5 buffer in a .308AR.  That buffer will be too long.  I know you gave a dimension, a length measurement, but then you also stated you're running the heaviest A5 buffer you could find.  The heaviest A5 buffer is the 6.83oz A5H4 buffer.  I know because I've got one in a 6 ARC gun right now. A5 buffers are 4.000" long, and they're only used in Small Frame ARs.  Never used in Large Frame ARs.

So, some clarification on those parts will be necessary.

You stated it's abusing you.  What's your history with shooting .308 Win? 

Everything else in your numbers look decent, and your parts list doesn't suck.  Your gas port is a touch smaller than I would recommend, for your barrel configuration - but it's working, and throwing brass at 1:30. 

Thanks for reading through this, I know it was long.

Thing 1: You're exactly right about the buffer tube, it's not a VLTOR product. I bought it off Clint @ HeavyBuffers.com. Here's the product info taken from his site:

Here's where I measured the *internal* depth myself:

I did email Clint about the depth, and he said it was normal and not a problem. But my BCG was within 0.05" of hitting the receiver, so I had to add quarters to make it work.

Thing 2: Not to worry, I'm not running the 4" buffer in this setup; if so, I'm sure we'd be having a very different conversation right now. The buffer I bought (the XH Carbine Buffer, also from Clint/HeavyBuffers) is 3.25" long, but weighs 8.5 oz (I confirmed this on the scale). Clint's website calls this the "heaviest standard length carbine buffer on the market." Here's a link to the page where I bought it: https://heavybuffers.com/xhcar.html

I might have been using the term "A5" a little reckless; it sounds like that might be more of a proprietary thing, specific to VLTOR, as opposed to a pattern. What I should have said was "A5-compatible" or something like that.

I don't have an extensive history in .308 Win, but I have shot several 308 AR's, including one of the DPMS small frame 308 rifles, and I can tell you that, for whatever reason, this build has turned out pretty violent, despite my best attempts to settle it down. The primary use for this gun will ultimately be whitetail deer hunting in the 100 - 400 yard range, but I'm not going to be much good with it if I can't tame it somewhat.

[98Z5V]

7 minutes ago, bugman said:

Here's where I measured the *internal* depth myself:

I did email Clint about the depth, and he said it was normal and not a problem. But my BCG was within 0.05" of hitting the receiver, so I had to add quarters to make it work.

Screw it in one more full turn. 

[bugman]

4 minutes ago, 98Z5V said:

Screw it in one more full turn. 

I'll have to file it down to get another turn. I'll give it a shot, but it might not look too pretty. Guess it'll be hidden anyway.

[98Z5V]

25 minutes ago, bugman said:

Thing 2: Not to worry, I'm not running the 4" buffer in this setup; if so, I'm sure we'd be having a very different conversation right now. The buffer I bought (the XH Carbine Buffer, also from Clint/HeavyBuffers) is 3.25" long, but weighs 8.5 oz (I confirmed this on the scale). Clint's website calls this the "heaviest standard length carbine buffer on the market." Here's a link to the page where I bought it:

Still, that's not an A5 buffer.  Conflicting information.  "A5 buffer" only means one thing. 

I run that exact same buffer in my .358 Winchester AR, straight from Clint, because that things needs that weight. 

25 minutes ago, bugman said:

I might have been using the term "A5" a little reckless; it sounds like that might be more of a proprietary thing, specific to VLTOR, as opposed to a pattern. What I should have said was "A5-compatible" or something like that.

Correct - and not even compatible, on a Large Frame AR.  Nowhere near hoping to be compatible.  It's very specific to VLTOR, and it only has a single purpose - make Marine Corps M16s with rifle stock, recoil identically when fitted with Carbine Recoil Systems.  The full A5 system is No Bueno on a Large Frame AR. 

25 minutes ago, bugman said:

But my BCG was within 0.05" of hitting the receiver, so I had to add quarters to make it work.

Every quarter is exactly 0.069" thick.  You added 2, so you added 0.138".  I'm seeing that measurement in the pic you posted is at 7 13/16" internal depth.  That's not normal.  That's 3/16" too much internal depth.  NOT normal. 

Screw that thing in another turn - get a pic of where it's at the in the lower receiver.  It should be about flush, top of extension, screwed in, to top of receiver.

Edited February 28, 2023 by 98Z5V

[98Z5V]

8 minutes ago, bugman said:

I'll have to file it down to get another turn. I'll give it a shot, but it might not look too pretty. Guess it'll be hidden anyway.

Dremel chainsaw sharpening bit does a wonderful job of performing this task.

Get that pic in here, of where the extension is, compared to the top of the lower receiver.  That's the tell-all, right there, on whether it's in there far enough.  If it's almost flush, or flush, that extension is out of spec.

Edited February 28, 2023 by 98Z5V

[bugman]

10 hours ago, 98Z5V said:

Dremel chainsaw sharpening bit does a wonderful job of performing this task.

Get that pic in here, of where the extension is, compared to the top of the lower receiver.  That's the tell-all, right there, on whether it's in there far enough.  If it's almost flush, or flush, that extension is out of spec.

OK, here are the pictures.

These first two are of the receiver extension as it was BEFORE giving it an additional turn. It appears almost perfectly flush to the receiver to my eye:

 

These next two are AFTER I gave it (1) more full turn. It's sticking out visibly now, by about 0.056" I measured.

 

What do you think?

[shooterrex]

By the top pic the tube needs to go one more turn. It's just barely catching the buffer detent.

However since the tube is squared off on the end that will not work.

Here are pics of a tube that would go one more turn and not stick out where the receiver would close.

[98Z5V]

Either the extension is out of spec, or the Aero M5 lower is. 

It was screwed in to where it should have been, in the first 2 pics, but barely on the retainer.  That doesn't really matter, as long as it catches the retainer, it doesn't matter by how much it catches it.  If it keeps it in there, then it's doing it's job.

In the second set of 2 pics, it's screwed in too far. 

So, screwed in to the proper depth, it's 7 13/16" internal depth, and that's counting a correct measurement - I saw it, I get it...  That's easy then - that extension is out of spec.  3/16" is ALOT to be over by.  Even if 2 quarters down the extension can make that issue go away, it's still not right.

This is one of the very few things in the Large Frame World where there actually IS a spec to follow, and it's Armalite's spec for a large-frame AR-10 Carbine Receiver Extension.  7 5/8" internal depth.  Not a little more, not a little less, not "close..."   7 5/8" internal. 

[98Z5V]

^^^  This is also the only reason that I'll use Armaite AR-10 Carbine extensions, or VLTOR A5 extensions.  Nothing else, just those two genuine products, and not something labeled "Like the Arma..."...

[bugman]

1 hour ago, 98Z5V said:

That's easy then - that extension is out of spec.  3/16" is ALOT to be over by.  Even if 2 quarters down the extension can make that issue go away, it's still not right.

Well, that is a shame. Wish I had that $85 back, I tell you that much. I'll give Clint another try tomorrow, but even if I did get the money back, I'm still not sure how I would spend it, other than getting a 7-5/8" tube that is actually 7-5/8".

After all, the rifle did run using the "extra deep" tube from Clint (after the addition of 2 quarters), but even with 8.5 oz of buffer and the Armalite EA-1095 spring, the recoil and ejection were about the same as everything else I tried.

If there are no further suggestions on what to try next, I may just take yes for an answer and be happy it cycles. That's leaps and bounds ahead of where I first started!

[98Z5V]

1 hour ago, bugman said:

After all, the rifle did run using the "extra deep" tube from Clint (after the addition of 2 quarters), but even with 8.5 oz of buffer and the Armalite EA-1095 spring, the recoil and ejection were about the same as everything else I tried.

If there are no further suggestions on what to try next, I may just take yes for an answer and be happy it cycles. That's leaps and bounds ahead of where I first started!

It's good that it runs, for sure.  Don't worry about where the brass goes, as long as it gets out of your gun, every single time.  If it's picking up the next round, and locks back on an empty mag, then very well - it runs.

Now, I saw 7 13/16" on your tape measure.  7 10/16" = 7 5/8".  You're 3/16" too deep.  You have two quarters in there.  Each quarter is 0.069" thick.  Quarters are hard to destroy, so they'll live happily down in the back of that extension, for just about forever.

However,  1/16" - 0.0625, so 3/16" has to equal 0.1875".   Those two quarters are 0.069" thick, each, so two are 0.138" overall.  Add another 0.069" to that, and you'd have 0.207". 

Put a 3rd quarter in there.   Just test it. You need to recover all of that 3/16" of that extension that you don't need.  The extra "too short" of 0.0195" won't make a difference, but it's the way to meet the standard. 

Give it a shot, literally.  Several shots.  See what happens. 

[MikedaddyH]

Hey just a thought. I had a similar situation with a AR9. It kept destroying buffers. Had five US quarters in the receiver extension. I switched to Canadian Quarters  and it worked. Maybe their coins are thinner.

[MikedaddyH]

16 minutes ago, MikedaddyH said:

Hey just a thought. I had a similar situation with a AR9. It kept destroying buffers. Had five US quarters in the receiver extension. I switched to Canadian Quarters  and it worked. Maybe their coins are thinner.

Size of US Quarter 1.75mm (0.069") thickness.

Size of Canadian Quarter 1.58mm

[bugman]

On 2/28/2023 at 1:34 PM, shooterrex said:

By the top pic the tube needs to go one more turn. It's just barely catching the buffer detent.

However since the tube is squared off on the end that will not work.

Here are pics of a tube that would go one more turn and not stick out where the receiver would close.

Thanks. Do you know the brand on that? I found one from V Seven but they are quite proud of it ($$$)...

[bugman]

1 hour ago, MikedaddyH said:

Size of US Quarter 1.75mm (0.069") thickness.

Size of Canadian Quarter 1.58mm

Thanks. I haven't had a chance to try out the third US quarter yet, but I'll keep working with this and hopefully find a good combination of coins.

[shooterrex]

40 minutes ago, bugman said:

Thanks. Do you know the brand on that? I found one from V Seven but they are quite proud of it ($$$)...

Not sure of the brand. It was in my parts box. It is standard ar carbine length pistol tube.

[98Z5V]

12 hours ago, MikedaddyH said:

Hey just a thought. I had a similar situation with a AR9. It kept destroying buffers. Had five US quarters in the receiver extension. I switched to Canadian Quarters  and it worked. Maybe their coins are thinner.

It takes $1.75 in US quarters to convert a pistol caliber carbine to a 3.250" buffer.  Been proven, more than a decade ago. 

Edited March 3, 2023 by 98Z5V

[MikedaddyH]

3 hours ago, 98Z5V said:

It takes $1.75 in US quarters to convert a pistol caliber carbine to a 3.250" buffer.  Been proven, more than a decade ago. 

Maybe so ... We got that bumpfire AR9 to work with 5 Canadian quarters. It was eating up buffers after every trip. That was like 7-8 years ago. Might have had a weird spring in it. Lots of parts got swapped out.

[98Z5V]

On 3/2/2023 at 9:52 AM, MikedaddyH said:

Size of US Quarter 1.75mm (0.069") thickness.

Size of Canadian Quarter 1.58mm

To make this easier for others to compare, that 1.58mm Canadian Quarter is 0.062" thick. 

Edited March 4, 2023 by 98Z5V

[bugman]

Just a quick update on this gun, in case anybody is still interested.

I felt like I had thrown too much money at this thing to just give up and let it continue to beat up my shoulder for all time. So I did a few more things:

1)  I ordered an Armalite receiver extension with the correct spec (7-5/8" depth), instead of using quarters inside that other thing I bought. The 3 quarters worked, but I just don't like doing that. I know that makes me weird. Anyway, I believe that solves any possible problem with my recoil system, since I'm already running the heaviest buffer and stiffest spring I can find.

2) I contacted Sprinco and talked to Alan Dugger, mostly just to make sure he wasn't aware of any other spring options that might work. He said Orange was the stiffest on the market, but he did suggest looking into a "configurable" gas tube, called EZTUNE from Black River Tactical. (Here's a link: https://blackrivertactical.com/WP/BRT-EZTUNE-Gas-Tube-Configurable-Midlength-p103167236) . 

I had no idea that a product like this even existed, but I guess it is supposed to perform the same gas-reduction function as an adjustable gas block, but without the hassle of having to adjust it, or the likelihood that it will eventually seize up. Do any of y'all have knowledge or experience with this?

3) I decided to hold off on the EZTUNE, and instead I called Criterion to ask if there was some mistake with my gas port size. I talked to Michael Ross, and he confirmed that the port size was indeed supposed to be in the range I gave, but could not understand the recoil and ejection problem either. He sent me a shipping label to send my barrel and upper (BCG and all) for him to look at. Not sure what I can expect Criterion to do about it....if the problem is that the port is too large, I'm don't know what can be done to fix that, other than possibly a new barrel. Anyway, I sent it off yesterday, and will update when I hear back.

Hope y'all are doing well.

[unforgiven]

Can you have a suppressor?