Aero Precision w/20" Krieger failure to feed using DPMS magazine

[Drew Eckhardt]

I finally got around to scoping and shooting my Aero Precision M5E1 15" mlok builder set with an Aero Precision BCG , 20" Krieger M110 AMU profile barrel, and Precision Armament M4-71 brake.  Running both Federal M80 and Hornady 168gr match It locked open on every shot and ran reliably with my ASC magazine;  but firing M80 had repeated failures to feed with a DPMS brand magazine having longer feed lips where the bullet ends up at the top of the extension and it might be a bolt over base situation although no ammunition damage results.

What would the ideal buffer weight be from 3.4 to 5.3 ounces (I have a heavier buffer body that adds 0.3 ounces and pair of tungsten weights that each add 0.8) to run reliably  and spot hits through my scope switching to an adjustable gas block,and Sprinco orange (11 1/8", 28 coils, .074") spring?

Specifics at the time included
1.  An LR308 recoil system using an AR stoner buffer
2.  weighing  3.7 ounces
3.  2.5" long
4.  In a 7 inch deep carbine tube
5.  With an AR Stoner spring, 11 1/2" long, with 28 coils, using  0.074" wire
6.  Using an AR -10 rifle gas system
7.  With a 15.5" tube 
8.  

9.

10.

 

 

11.  .875" gas journal diameter, gas port between my .092" and .093" +0, -0.0002" pin gauges
12.   ASC magazine which works well on left, DPMS magazine which fails on right.  The DPMS feed lips are Magpul Pmag length although I haven't tried one of those yet.


The barrel extension has M4 feed ramps, receiver hardly any which would be OK on a .223 AR



Other less relevant specifics are a Magpul CTR stock set to A1 length, LaRue RISR that gives me a solid cheek weld but moves to allow charging, Geissele Hi Speed DMR trigger, Nightforce NX8 2.5-20x50 Mil-XT on a Nightforce 1.375" 20 MOA extended Unimount, and Harris 6-9" bipod.   It was laser accurate, recoiled less than my 9 pound .223 AR, and was perfect apart from the magazine sensitivity that has me speculating about having too much gas or too little buffer.

Edited April 2, 2021 by Drew Eckhardt
More pictures

[Drew Eckhardt]

On 4/1/2021 at 11:26 PM, Drew Eckhardt said:

I finally got around to scoping and shooting my Aero Precision M5E1 15" mlok builder set with an Aero Precision BCG , 20" Krieger M110 AMU profile barrel, and Precision Armament M4-71 brake.  Running both Federal M80 and Hornady 168gr match It locked open on every shot and ran reliably with my ASC magazine;

That is, it locked open when I let either magazine run dry.

It ran all the way through the 10 round ASC magazine, but had repeated hiccups starting with a fully loaded 10 round DPMS magazine.

Starting with the bolt latched it fed reliably from both magazines.

Edited April 2, 2021 by Drew Eckhardt

[sketch]

sounds pretty good to me for build specific.. Id chalk it up to mag probably. do try a magpul sr25, if you could? I have had to bend maglips on metal mags also, different platform.  I'm no guru.. there is gonna be somebody that knows more . 

m5e1 looks nice! 🍻🇺🇸

Edited April 2, 2021 by sketch
shits

[392heminut]

I would go ahead and bump that buffer up to the 5.3 weight. That's the weight these things were originally designed to run with and it will work fine with the Sprinco orange spring.

[Drew Eckhardt]

I bumped my buffer weight to 5.3 oz, swapped in the Springco orange spring, and installed my Sentry 8 adjustable gas block.

It moves less than before the adjustments, but still has bolt over base malfunctions using the DPMS magazine when set for minimum gas to lock open on empty.

Given reliable function with the ASC and a PMAG, I'm going attribute my problem to the longer DPMS feed lips and not use those magazines.

Bolt over base malfunction using DPMS magazine, but just enough gas for bolt hold open on empty:

Which I attribute to feed lips slightly longer than my other magazines

I'm just going to leave the DPMS magazines in a box and enjoy my rifle:

[98Z5V]

Nothing wrong with the recoil system that you ended up with - but I'd save that for another build.  I'd scrap the whole recoil system, total, and just put the Armalite AR-10 Carbine Recoil system in.  Completely.

This one:

https://www.armalite.com/SACItem.aspx?Item=AR10REKIT01&ReturnURL=/Armalite/Product-Category/AR10-Parts-Accessories/Lower-Receiver-Parts&Category=ac614400-ff09-4cdf-9d35-419a654e7201

You spent the money on the Krieger M110 barrel.  Use the recoil system that the M110 uses, when it has a collapsible stock. 

Edited April 6, 2021 by 98Z5V

[Drew Eckhardt]

On 4/5/2021 at 10:56 PM, 98Z5V said:

 

https://www.armalite.com/SACItem.aspx?Item=AR10REKIT01&ReturnURL=/Armalite/Product-Category/AR10-Parts-Accessories/Lower-Receiver-Parts&Category=ac614400-ff09-4cdf-9d35-419a654e7201

You spent the money on the Krieger M110 barrel.  Use the recoil system that the M110 uses, when it has a collapsible stock.

 

I'd try that in a heart beat except the parts are back ordered with an unknown delivery date.

I can get an A5 buffer tube and H3 buffer from other sources, but the spring is a wild card.

Anyone know the Armalite spring  parameters?

I have a Fulton Armory .308 rifle spring measuring 12 5/8" long with 39 .078" coils, but no clue how close it is.




 

[Drew Eckhardt]

I ordered an Armalite AR10 spring a few weeks ago with plans of trying Eugene Stoner's proven combination sometime, but will be pleasantly surprised if that happens in the next few months.

[98Z5V]

13 minutes ago, Drew Eckhardt said:

I'd try that in a heart beat except the parts are back ordered with an unknown delivery date.
 

When you call Armalite on the phone, and talk to the people there, they magically find all the parts for the kit for you and ship it out.  No kidding.

The Armalite EA1095 spring is in stock right now at DSG Arms.  Here's the link.

https://dsgarms.com/lower-receiver-parts-armea1095

[Tack14]

On 4/4/2021 at 12:33 PM, Drew Eckhardt said:

I bumped my buffer weight to 5.3 oz, swapped in the Springco orange spring, and installed my Sentry 8 adjustable gas block.

It moves less than before the adjustments, but still has bolt over base malfunctions using the DPMS magazine when set for minimum gas to lock open on empty.

Given reliable function with the ASC and a PMAG, I'm going attribute my problem to the longer DPMS feed lips and not use those magazines.

Bolt over base malfunction using DPMS magazine, but just enough gas for bolt hold open on empty:

Which I attribute to feed lips slightly longer than my other magazines

I'm just going to leave the DPMS magazines in a box and enjoy my rifle:

Very nice g roup.  I don't know much about quality of mags but read many many many good reviews about C Products/Duramag stainless steel ones so I bought those.  Not seeing many out there right now from authorized dealers but did get a few before all went out of stock.

[98Z5V]

In the old days, the biggest mag that DPMS made for the LR-308 was a 19-round mag - and those original, old mags had feedlip problems.  Several people on the internet figured it out, came up with a tweak, and fixed those jacked up 19-rd mags that DPMS shipped. They magically worked after that.

Now, in light of that, here, I'm wondering when your DPMS 10-rd mag was made, and if they were doing the same thing then, to the 10-rd mags that they did to the 19-rd mags.  If so, you can search the interwebz and find "the fix for the DPMS 19-rd magazines" and possibly solve the issue with this 10-rounder that you've got.

Worth a shot, anyway.  You might be able to put that mag into the rotation, if the 19-rd fix works. 

If it doesn't fix it - it goes in the trashcan or sits unused - like it will right now anyway.