Built a .308 AR, having ejection issues. Any Ideas?

Mike Shoots Stuff

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I recently finished up an AR in .308 that I built piece by piece for the most part. With only 100 rounds through it, I have had more then 1 in 10 rounds have failures to eject. Sometimes the case gets caught in a stovepipe, a few times the case would just flip around in the port and be facing backwards. So far I've fired (20) Winchester 147 grain rounds, (50) Atomic 168 OTM and (30) M118 LR rounds. All have given me ejection problems.

The Barrel is a Black Hole Weaponry 308B 1/11 SS 5R with mid length gas system
BCG is nickel boron coated by JD Machine
Receiver is DPMS
Buffer is H3 carbine with the spring to go with it
I don't close the ejection port when I load it or between firing

The Ejector feels like it has good spring to it when I press down on it. Does anyone have any other ideas? Right now I'm not sure whether I should spend any more money trying to work the kinks out or just take it apart and sell the pieces separately and save for something else.

 
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Bravo Hotel

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It looks like a nice piece of machinery and has good bits and pieces - Don't quit on it so early in the program.

When it ejects properly, how does the brass exit and how far does it go? If it is going behind you and heading for the horizon it may just be way overgassed. That would not be too much of a surprise with a mid-length DI gas system.

You could try fitting an adjustable gas block - either home made or store bought which wouldn't be too expensive. Then turn it down to minimum and work your way back up to a reliable bolt lock back using a known good magazine. Test with the lowest pressure rounds you plan to use and you'll be good with anything higher rated.

Does the rifle do this with all your mags? It's possible that it is caused (or contributed to) by the mag but doesn't sound very likely.

Also - the poor thing is nowhere near 'broken in' yet. Clean - Inspect - Shoot your way through another couple of hundred rounds first. I'd put money on the 'overgassed' theory but it may heal itself.

Good luck!
 

ole'soldier

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Double Check your gas block. I used a low profile Yankee Hill block on my last build. It came with no instructions and I left the gap that would normally be filled by the plate that the hand guards clamp on to. When I function checked it the first time the BCG wouldn't feed and closed on an empty chamber. When I got home I went to YH's site and found a PDF that stated not to leave that gap for the low profile block only. When I pulled the gas block off it was pretty evident that the port was mostly covered and very little gas actually made it to the gas key. You could have similar issues. Also, is the H3 right for a mid-lenght gas system? I haven't worked with that gas system to know. Maybe the buffer is too heavy?
 

30calDeath

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I had issues using a Slash's Buffer in my REPR, I went back to the stock buffer and spring and wa la all my short stroking issues disappeared. So I would look at your buffer/spring combo if I were you.
 

Texar2

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The case flipping backwards, was this on the last round when the bolt was held open?
 
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Texar2

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I think your rifle is displaying symptoms of being under gassed. That does not mean it is under gassed. It could mean that you have a short buffer tube and the bolt carrier is rebounding too quickly. Is your tube commercial or milspec? It could also mean that you have the wrong combination of spring and buffer. There are several different length springs as well as buffers. Sometimes coated bcgs can need breakin. Slop the bcg in mobile one oil and see if that helps. These are things I have seen in the past. Let us know whats up.
 

DavidAR10

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With the usual suspects already mentioned,

I say that your extractor is slipping off the head.

It could be from a weak extractor spring, over gassed, debris caught in the extractor's claw or multiple reasons.

For the first two that I mentioned, I took two d-Fender rings, stacked 180 of each other, placed them over the extractor spring.

David Gilhausen(sp) gave me that fix for my second AR-10T back in 1999.

EDIT: An o-ring of the proper size and material will fix it with less coin than two d-Fender rings. BUTT!!!
d-Fender rings last forever.

And don't rule out a Slash Heavy Buffer if the o-ring fixes things. Odds will be that you are over-gassed.
The buffer will give you a longer dwell time along with all of the bennies that go with that.
 
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Paulyr450

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I had the same problem when i put my bhw 243 barrel on. I could not figure out how it flips the case around and jams like that but then i looked at the case head and noticed it was bending the shit out of the case lip. I ordered an pri adjustable gas block and it runs perfect after tuning it. Your gun is just overgassed. The mid length gas system is probably really making things worse.
 

Unknown

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in addition to the above suggestions, check extractor pressure. If the extractor has too much pressure, it forces the case onto the other side of the bolt, and the ejector can't push it off fast enough during the recoil/reload cycle.
 

sinister

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What length is your receiver extension/buffer tube (7 or 7 1/2 inches)? If you're using the shorter (5.56) extension you're not getting a full carrier stroke and the case may get caught in the ejection port instead of being thrown overboard.

Are you using a 308 or 5.56 spring?

Did you lube the bolt in the carrier, and the carrier in the upper (sloppy wet)?

At only 100 rounds your weapon is nowhere close to being broken in.

Good looking rig.

ar10-ar15buffertubes.jpg


A 7.62 bolt carrier is longer so you either need a longer extension (if using a 5.56 buffer) or a shorter buffer (if using a 5.56 extension -- the following drawing shows why when using a fixed stock):

post-530-0-98290400-1363297082.jpg
 
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arnie19

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I had similar problems with a 308 upper I bought supposedly from a company that isn't well liked here .I fixed mine by comparing the ejector spring and extractor spring with another bolt head known to work good .Mine were noticeably weaker so I replaced the ejector spring and the extractor spring plus put an O ring over the extractor spring .Now it works great .
 

Mike Shoots Stuff

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Thanks for the help. The Buffer I bought is shorter to allow the longer carrier to cycle completely. The spring I bought came with it. Over-gassed is what I'm hearing a lot on some other forums as well. I think I will try an adjustable gas block first and tune it. If this doesn't work I'll try one thing at a time until it does. However. I live in Hawaii and couldn't bring this gun with me. So I will try this once I get back to California where my rifle is legal.
 

AXEMAN

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try a stock DPMS 308 rifle or carbine buffer and matching/appropriate spring first as a baseline. im not saying don't use a heavier buffer ever, but start with a factory set up. the 308 world has different specs than the ar15 and not all combos work with everything. with an endine and tubbs flat spring I couldn't lock the bolt at all. after the factory carbine and spring, no issues. I always start stock and then add heavier buffer/spring combo if needed. as pictured by others, 308 stuff and 223/556 stuff isn't all the same size. I didn't know the tubes were different lengths until I saw this thread. but my ACE SOCOM stock for a 308 is longer than the one for an ar15 so it makes sense

I have the same barrel and gas configuration from bhw. mine was the 3 groove poly rifling. I used an adjustable gas block from the start. I really need to run more loads thru it, but so far no issues with a bone stock set up. ill try the endine again later as I get to shoot more
 
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tipper

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This is the first thing to try, ejector spring to heavy will turn case around will also flat spot the case neck as it slams it against the receiver coming out of chamber, clip a coil or 2 off spring.
If the ejector spring is to light it will drop the case off straight or stove pipe it.
Over gas, under gas, BS
 

ktech_stl

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1) Did the brass stovepipe with the base or the neck of the cartridge in the chamber?
Base is usually related to either ejector/extractor issues, or more likely overgas or undergas. Stovepipe on the Neck can be a whole slew of other issues and more difficult to discern.

2) Do you ever have failure to hold opens on the last round? That is a primary indicator of undergassed and I would ditch the heavy buffer for a conventional one to see if that solves your problem.

3) What is the ejection angle? If the cases are ejecting forward of 2:30 o'clock, then you are for sure overgassed.

If you are ejecting forward, the bolt carrier is likely moving back too fast to allow the center of mass of the case to rotate out of the chamber. Typically in the overgas case, you would see under high speed video that the cartridge starts to rotate out of the chamber, but loses angular rotation as the case is pressed forward by the ejector and the case travels back at some angle to the axis, but doesn't continue to rotate out, which means the flat front of the brass deflector/end of ejection port becomes the brass deflector, instead of rotating around this and hitting the brass deflector on the sloped surface. This causes the case to rebound straight forward and perpendicular to the axis of the chamber, with the base of the cartridge still in the ejection port where it gets trapped on closeup - classic Failure to Eject/Stovepipe.

I hope this helps. You are already running a heavy buffer, which eliminates that option for slowing down the system. Recoil springs may help a little bit, but not much. The bolt velocity is determined in the first 5/8" or so of bolt travel while the carrier is still accelerating. The spring constant doesn't really help at that point of the cycle.
 

biggin69

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I built a 308 carbine using a Mega Arms upper/lower and a DPMS 16" barrel. I had the same issue with the gun being over gassed. Combinations of springs and buffers helped a little but did not solve the problem. I then installed a SLR adjustable clamp on gas block DA7 Adjustable Gas Block and problem solved. I cannot say enough about how happy I am with this block. Adjustment is from the front. The adjustments are indexed by a detent pin system. I highly recommend this to fix your problem. Good luck!