Cycling issues looking for input

[lamrith]

Hey all put some more rounds thru the grendel tonight. Still shooting 123G Amax Factory ammo only. Just hit the 100rnds mark on the barrel. The lower is one I have had for a long time and works great with my other uppers, only "issue" I have ever had is ejecting brass forward.

So tonight I chrono a few rounds and was working fine. Finished that box and opened up another box from another lot. RSO was curious about the gun and round so I handed him a mag with 2 rounds in it. Fires 1st round and the second round stovepipes. Go to look for ejected round and can't find it, because it is still in the chamber. Lower bolt on it and pull back by hand and case comes out easy. Tried the second round it loaded fine shot and ejected fine. Continued thru the box and every few rounds it would leave one in the chamber. I tried rounds from another lot and had NO issues with that lot.

My concern is that this gun is going out of state with me in Oct and I need it reliable. I have boxes of the good lot still but I would rather make sure she will eat any factory round..

I have been shooting AR's a bout 2 years and never had this happen before. Is it maybe overgassed? The brass shows signs of the ejector ripping at it.
Would maybe an Adjust gas block help?
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[montana]

I would pull the bolt apart and inspect the extractor, ejector, and both springs first. I would then make sure the bolt carrier key was tight and not loose. I would then check the gas tube and make sure the button end wasn't worn and sits inside the key with out issue. I would also use a known reliable mag to eliminate a mag issue. Brass ejecting forward doesn't necessarily mean it is over gassed. I had a over-gassed 18" barrel that wouldn't even eject the brass or cycle it reliably at any time. The brass just fell out or sat in the upper receiver jamming the rifle. Since you have had it shoot reliable on and off I would tend to think you have another issue other than over gassing.

[Bwild97]

Looks to me like you have a 5.56 extractor on your Grendel bolt. You can fix it with a jewlers file.

What is your bolt face depth?

[1911man]

I would check your gas block first to see if its still tight. I had one in the past that loosened up and it cause it to cant just slightly to the right making it to where it was just a little off center from the gas port on the barrel. It did exactly what you are describing.

[LRRPF52]

Barrel?
Gas system length?
Recoil system (rifle, carbine, what buffer weight, etc.)?
Assembled by?

[lamrith]

18" Brownells barrel with matched by Brownells bolt.
Midlength gas
Std plain jane carbine buffer and spring
Upper assembled by me. Upper, Bolt Carrier, barrel nut, gasblock and handguard were pre-existing from another build.
Lower have used with Many uppers.

Not had an ejection problem until lastnight. Literally round #101 from the gun was the 1st to do this and was round 81 out of that same lot of Hornday 123G Amax (LOT#:3141968), which is the 1st I bought. Moments before this failure I had fired 5 rounds (to finish a box and chrono) from my second lot (Lot#: 3131866). The 60 rounds of the original lot and 40 from the second lot had all fed and ejected just fine prior to this. I have considered a heavier buffer like an H3, but thought that maybe a gas-sblock was the more proper solution and would allow the upper to be put on any lower without needing a heavier buffer setup?

I will verify gasblock is tight, tube is aligned, key is tight. Not taken a bolt apart before, this bolt came with the barrel matched from Brownells. Yeah I thought it was wierd that the bolt would not extract it during firing cycle, but that dropping the bolt and then pulling the charging handle the brass ejected with no hassle, not tight at all. I saw the brass in the chamber and went ohh craap, I got a stuck case. But Charge handle had very little tension beyond the buffer spring compression when I manually cycled it. That is what made me think maybe the bolt was cycling to hard and seeing the gouges on extractor lip..

[coyotetan]

I had the same problem with matched barrel and bolt, I replaced with a underground tactical bolt and added an adjustable GB, problem solved

[LRRPF52]

The barrels on the ones I've seen from Brownell's have a .094" gas port diameter on a MLGS. That's a lot of gas driving the action.

Try a heavier buffer, or the JP SCS, or an adjustable block.

I have a Satern 18" MLGS with .094" gas port, and it runs like a raped ape with the PRI adj gas block turned almost all the way down, with a rifle buffer and recoil spring. I can only imagine what it would do without adjustable gas.

Gas ports should be .076" for MLGS 18" barrels, as there is a lot of dwell time.

Stove pipes and forward ejection are commonly symptomatic of over-gassing, and the resulting excessive cyclic rate. Based on what you're telling me, I suspect this is what's going on.

The initial 80rds fouled up your gas block and provided a better seal, and now there isn't as much leakage, so the gun is cycling faster, not giving enough time for the bolt, extractor, and ejector to manage the spent cases optimally.

[lamrith]

Thanks LRRPF52, I had a feeling you would dial me in.

[lamrith]

Don't have adjustable gas block yet, but a buddy is loaning me a H3 buffer to try short term. Got my existing oen measured and it is 2.9oz. the H3 is 5.5oz. Hoping it will tame things a little bit, I have hard cycling in my 300blk (16" pistol gas) and 9mm, so I might just bump all three of my lowers up to H3 if testing goes well this week.

I would like to make it so that my uppers/lowers are inter-changeable within the constraints of the law so that if I have a problem with one I can swap in another lower and continue my range trip/hunt.

[LRRPF52]

The 18" Satern with the gas turned almost all the way down on the PRI Adj block runs like a raped ape with a rifle 5.1oz buffer and rifle recoil spring, just for reference.

[lamrith]

Thanks LRRFP!!
I also added an Oring under the extractor just in case to make sure it was getting a firm "Kungfu" grip.

Hopefully the rain holds off tonight, want to hit range after work and function test as well as chrono both batches to get same time & temp side by side data of both function and velocities.

[lamrith]

Well the H3 buffer and Oring added to ejector seem to have helped. I shot 10rnds of the "bad" lot today and not a single issue. Also 10 of the good batch and also no problems. I also noted that it was ejecting more in the 2:30-3:00 region instead or 12:13-1:00.

I will keep an eye on it and let folks know bot for now I think I have found a happy and inexpensive solution...

[LRRPF52]

I actually like to stay away from over-sprung extractors, and let the spring weight balance out between the ejector and extractor.

High strength extractor springs make it more difficult for the extractor to snap over the case rim as the BCG goes into battery, creating sluggish forward movement on the last small distance of forward bolt travel, where action spring strength is least effective.

It's a common band-aid for violent and early unlocking, but I prefer to address the gas system, which is the root of the problem in these cases. Reduce excessive gas flow into the BCG, in order to tame cyclic rate, and get the parts behaving nicely, smoothly, as they were designed.

[lamrith]

As always good advice. Just had to try it this way since it was a free possible fix. I like the theory though of the adjust block to fix the overgas problem rather than bandaiding it by making the reciprocating mass higher to counteract it..