Trouble with (lightly MODIFIED) factory BCM M4, looking for some diagnosis help

[SheriffofMDC]

Carbine is a BCM factory complete 14.5" mid length lightweight BFH barrel with surefire warcomp permanently attached.

-FSB was chopped and reparked by ADCO, who also installed warcomp and KMR-A handgaurd.

-lower is as came from factory with H buffer, and buffer spring is at correct length.

-Ammo used has exclusively been new manufactured American made 223 head stamped 55 FMJ, mainly federal but also some Winchester. Also some Winchester Ranger 223 55 ballistic silver tip.

-Magazines have been mixed Pmag, BattleMag, BCM aluminum, ETS, and Lancer 30 round mags.

-Total round count around 2.5-3K

So problem is I have been having failure to eject. At first I thought it was a double feed issue and was maybe magazine related. However, I tried several other mags which are known to be reliable as well as brand new out of the wrapper mags.

As I started paying attention I noticed that it was failure to eject. Even had a stove pipe that was text book perfect. Never even seen something like it while setting it up in training.

Per BCM I tired mix and matching lowers, uppers, and BCG. I did so with a Colt LE6920, still had issues.

So complete upper receiver group and complete BCG was sent back to BCM. They found bolt carrier to be at minimum spec and replaced it. They also rebuilt the bolt with new everything, and replaced the gas tube. They said everything else was in spec.

Got it back and issue still exists.

Surprisingly for a mid length firing 223, empty brass is ejecting forward to 1-2 o'clock. Malfunctions happen at random.

Tried a complete Daniel Defense BCG which has the O-ring around the extractor spring and empty brass instantly began to eject correctly to 3-4 o'clock. Didn't have enough ammo left at that point to really run it, so only 40-50 rounds.

Brass deflector does have brass marks on it and it's enough that I doubt it got there only from the last 40-50 rounds fired. Complete carbine has always been properly cleaned including use of a chamber brush, and properly lubricated with slip 2000.

So I'm at a bit of a loss. I'm at either it is cycling too fast and that's why it is failing to completely eject at times and why it is spitting empty brass forward. OR the exact opposite and maybe it's cycling too slow, BCG is not making it all the way back and as it returns back into battery it's hitting brass that is clearing the ejection port and sending it forward. Perhaps that's why the O-ring equipped bolt seems to have cured the ejection pattern, but I don't think that explains the brass marks on the deflector.

BCM has been helping but a little less than desirable. They did send me an O-ring to try with their bolt. Just haven't had a chance to make it to the range yet and try it out.

Thanks in advance for th thoughts.

[MistWolf]

I know BCM is a reputable company, but The O ring under the extractor isn't the right fix. Replace the extractor spring with an M4 extractor spring from Colt or Sprinco.

There are too many variables involved to use ejection pattern for reliable troubleshooting.

[hk_shootr]

You did have the upper modified, many companies would not have taken a look at it at all

I would also suggest replacing the ejector spring also

[bp7178]

Replace the extractor spring with an M4 extractor spring from Colt or Sprinco.

This. Be sure to inspect the extractor as well.

[Iraqgunz]

The clue here is that you swapped the BCG and now the issue appears to be fixed. Now you need to go further by swapping carriers and bolts to narrow it down further. I also agree that the O-ring is not the cure. You need to get a new extractor spring, but not replace it until you have troubleshooted it more. The BCM enhanced spring, Colt or a Sprinco are good choices.

[Crazydave]

BCM actually makes a Bolt Upgrade Kit to replace the spring, the o-ring, extractor, etc

https://www.bravocompanyusa.com/BCM-...d-bolt-kit.htm

Sent from my SM-G950U using Tapatalk

[LMT/556]

People place too much emphasis on ejection pattern. My 18" intermediate w/FABCG and H2 buffer ejects at 1-2 but so softly they are just off the front right corner of the bench, occasionally I've had them stay on the bench. I generally use Colt copper springs whenever I get around to replacing whatever came stock. The pattern in my rifles I believe is from them bouncing off the front edge of the deflector/ejection port then forward at 1-2 o'clock from the brass witness marks.

Our BCM midlengths are a steady 3 o'clock, the Centurion around 4. They all get a mixed diet of 5.56 pressure brass ammo.

I'd maybe look at your ejector. With that round count a weak spring or accumulated crud possibly contributing. Hornady One Shot works wonders for those areas.

Notice in that upgrade/field service kit there is no ejector, spring or roll pin. Is it possible their rebuild didn't touch the actual ejector at all?

[Circle_10]

I had a similar sort of issue in a carbine that I built using a BCM BCG,. If I remember correctly the failures to eject I were getting were probably related to the extractor slipping off the rim of the fired case during extraction. I replaced the BCM extractor spring and insert with one of the Colt Gold springs and had no more issues.

[SheriffofMDC]

Yes it was modified by having the factory A frame cut down.

I asked BCM to send it back to have them check it to see what the issue might be and that I would pay for the inspection and repair. That was after I tried their suggestion of mix and matching upper, lower, and BCG. I asked them to sell me the O-ring by itself and they sent the bolt kit at no charge.

Because I have no expectations of them paying for the repairs/replacement I have just wanted more engagement from them on possible causes so I could try to figure it out and resolve it on my own. When the upper was returned to me there was no letter from them, no email nor a phone call describing what they found and/or did. I had to contact them and request that info. I have been very detailed and specific with the issue but have not received the same from them in discussing it and that's why I'm not totally thrilled with their response but also not angry. So no worries I'm not trying to bash a financial sponsor of this forum. I have another BCM, very similar build, that has been flawless.

Back to the point;
I did run the gun with a complete Colt BCG from an LE6920, and still had the same issue.

BCM said that they rebuilt the bolt when they had it so new springs, extractor, etc.

Only difference so far has been seen with the O-ring equipped DD BCG.