View Full Version : So, this happened while shooting my newest rifle...five times during one magazine
The gun:
54450
It's a BCM 14.5" standard lightweight mid-length barrel, upper is a slick side from JSE Surplus.
The barrel extension has extended feed ramps, the upper does not.
Buffer tube, action spring and H buffer are all BCM, as well as the bolt carrier group.
Here's what happened:
54451
The dents you see are from the lugs on the barrel extension, the rounds were jamming in the upper at an angle.
I should add that this rifle has functioned flawlessly when shooting XM855 and using Magpul/Colt/Okay magazines.
This time, I was using an HK magazine and was shooting Lake City ball ammo.
I should also add that this same magazine and ammo fed fine out of two other rifles on the same day, for some reason this rifle did not like this ammo/magazine combo.
Thoughts?
Edit. What did BCM say? Call them first, but if you want to troubleshoot yourself:
Ive seen that from a bent extractor.
Change the bolt, if fixed, put the old one back in but swap extractors with a different rifle. Or lat the extractor on a flat surface. I suspect a bad extractor spring could also cause this.
Could be mags. What I think is happening is that the round being fed is getting loose before or during the feeding process.
In the case a saw, the extractor lost control of the case, it bumped the top round of the mag knocking it loose as the bolt was trying to feed it. The empty case then exited the port.
rakkasangrunt187
11-09-18, 11:30
The gun:
54450
It's a BCM 14.5" standard lightweight mid-length barrel, upper is a slick side from JSE Surplus.
The barrel extension has extended feed ramps, the upper does not.
Buffer tube, action spring and H buffer are all BCM, as well as the bolt carrier group.
Here's what happened:
54451
The dents you see are from the lugs on the barrel extension, the rounds were jamming in the upper at an angle.
I should add that this rifle has functioned flawlessly when shooting XM855 and using Magpul/Colt/Okay magazines.
This time, I was using an HK magazine and was shooting Lake City ball ammo.
I should also add that this same magazine and ammo fed fine out of two other rifles on the same day, for some reason this rifle did not like this ammo/magazine combo.
Thoughts?
Did you use the XM855 on same mag? Some mags just don’t work well with different ammo. For example, one ammo I used did well with standard mag but did not like Magpul or Lancer mags. The problem it seems stems from the feedramp... Something is happening there that may be hitting the bullet in the chamber once it is seated when bolt is racked forward. It could also be the way the bottom of the casing of the particular round that like city ball is using. It might be loose enough to cause a slight angle when bolt is going forward.
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...I suspect a bad extractor spring could also cause this.
Yes. Yes, it does.
...the extractor lost control of the case, it bumped the top round of the mag knocking it loose as the bolt was trying to feed it. The empty case then exited the port.
Typical of an extractor issue, resulting in the damage shown on the cartridge.
https://www.m4carbine.net/attachment.php?attachmentid=54451&d=1541780607
It's likely the HK junk mag. Is it one of those problematic steel mags?
I have not called BCM, figure they will tell me to kick rocks since it's a Frakengun.
The HK magazine is definitely steel and the follower is metal, not sure if it's one with a known issue but if it is I'm throwing it in the trash.
This did not happen when using PMAG's or aluminum USGI's.
As for the extractor being bent, not really sure how to check it since only the sides have level surfaces...
54452
Sample of one, but my HK steel mag is problematic. I would try any of the mags you mentioned and the ammo you had an issue with.
Sell the HK magazine. Take the 30 bucks and buy 3 Okay aluminum magazines. It's probably not contributing to the issue but I would feel better with the M4 ramp cuts in the receiver. It isn't difficult or expensive to do.
I didnt know HK mags had a rep, I thought they were all good.
Absolutely could be a mag issue(mechanically). Mark the mag, keep shooting, track malfunctions, and if its always that mag, trash it.
HK rifle mags are great for propping my garage door open.
Hard to say but this could also be the result of short stroking, where the bolt lugs don't travel rearward enough to clear the rim, then as the bcg travels forward the bolt carrier catches the rim instead of the bolt. Then the cartridge gets wedged in there with the feed ramps putting the dents in it.
I would guess he didn't call BCM and even if he did contact them, it's Friday and we all know no one is going to answer until at least Monday or Tuesday. In addition, though he is using some BCM components, he has clearly assembled this with a non-BCM upper.
Edit. What did BCM say? Call them first, but if you want to troubleshoot yourself:
Ive seen that from a bent extractor.
Change the bolt, if fixed, put the old one back in but swap extractors with a different rifle. Or lat the extractor on a flat surface. I suspect a bad extractor spring could also cause this.
Could be mags. What I think is happening is that the round being fed is getting loose before or during the feeding process.
In the case a saw, the extractor lost control of the case, it bumped the top round of the mag knocking it loose as the bolt was trying to feed it. The empty case then exited the port.
Personally, I’d ditch the HK mag and extractor o ring and go from there.
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Man I had no idea these mags were known to be junk, I just went through all of my magazines and found over a dozen.
I got a bunch on sale a long time ago not knowing they sucked or that replacement parts were non-existent.
They are now quarantined, thanks for all of your input.
As for the o-ring around the extractor spring, why is this bad?
I have installed them in all of my rifles except for my A1 clone.
I own a lot of magazines and the numerous HK magazines I own work just as well as the aluminum GI mags. I don't shoot a lot of LC ball out of any magazine but I reload various 556 bullet types/weights and have never had a malf from an HK magazine. 77gr SMK's / TMK's feed flawlessly through HK Magazines into both of my MR556 rifles as well as numerous other 556 rifles.
Well, considering I've never had feed failures like this with polymer or aluminum magazines, these are going into the "DO NOT USE" box.
I'm not going to keep mags in circulation if they work in some of my rifles, but not others.
I'm going back out this weekend to shoot more of the same ammo with different mags.
This is not a BCM rifle, it's a home built gun for all the people telling him to call BCM. OP, check your carrier key, and check your gas block, this could be a gas issue. I have seen this exact thing happen due to short stroking because the carrier key bolts backed off and it became loose. The BCG does not get enough gas, it short strokes and the bolt lugs catch the side of the cartridge as it comes forward, and wedge the cartridge in at an agle and dent the brass. In my case torquing the carrier key screws back down fixed the issue.
My novekse loved to do this. The barrel extension "corners" on the inside were very sharp. The round pivots on these as it slides forward into the chamber. If they are too sharp, they did into the case and arrest its movement. You will note significant shaved brass in the pre-chamber area. The magazine feed angle can help or exacerbate this issue.
The 3rd Ranger Battalion and Regiment teams nearly lost the 2004 Army Rifle Championships due to the then-new HK mags. A runner from one of their supply rooms saved their butts with a box of GI mags.
It’s the HK magazine.
Went out yesterday and it functioned perfectly using PMAG’s and Okay mags with Magpul followers.
I tried and could not duplicate the failure with ball ammo and also fed it some HSM 75gr OTM’s, I had one double feed with one of the older Okay magazines.
I have checked the gas key screws and also looked for leakage around the gas block, I don’t think it is short stroking.
What threw me off was the fact that the suspect HK mag worked fine in a couple other rifles but in this one I had several failures, I won’t be using HK mags anymore.
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