View Full Version : Formerly reliable BCM 11.5" upper has sudden issues PART II
Thanks to everyone's advice I fixed the cycling issues I was having by replacing the gas tube, as the carrier end had worn smooth and was no longer sealing properly on the gas key.
https://www.m4carbine.net/showthread.php?210796-Formerly-reliable-BCM-11-5-quot-upper-has-sudden-cycling-issues (Formerly-reliable-BCM-11-5-quot-upper-has-sudden-cycling-issues")
HOWEVER,
My upper has now decided to have doublefeed malfs. Several per mag. Magazine choice doesn't matter.
I swapped the BCM BCG out with the PSA $60 BCG that was recently on sale, and the doublefeeds stopped. The recoil with the PSA unit is MUCH sharper than the BCM, but I can't see any noticeable difference between the two BCGs. I'm assuming the extractor needs to be replaced or adjusted, but I can't figure out why the recoil is so much different between the two. Am I losing gas somewhere with the BCM?
Are you talking about true double feed, where two live rounds are jammed in the action? If it's a true double feed, it's your magazine.
Or are you talking about an empty and a live round jamming the action? If it's an empty and a live round jamming your action, you have a problem with your extractor, most likely the spring.
Why did it show up after fixing your gas leak? Because the extra carrier speed is placing more strain on the extractor. With the added strain, the extractor is losing control of the extracted case before it can be ejected.
I'll go a little further on Mist Wolf's explanation and add that the reason the PSA's BCG recoil is much sharper, and it extracts whereas the BCM BCG does not is due to not only a fresh extractor and spring on the PSA, but a better gas seal elsewhere, probably in the gas rings. You also might want to check the ejector on the BCM bolt.
Should be a relatively easy fix, and you have two good BCG's:
https://www.bravocompanyusa.com/BCM-SOPMOD-Bolt-Upgrade-Rebuild-Kit-p/bcm-sopmod-bolt-kit.htm (no ejector parts)
https://palmettostatearmory.com/bolt-componet-repair-kit.html (contains ejector, ejector spring and ejector roll pin)
As Mist stated, we need to determine if this is a "double feed" or a failure to extract and then a failure to feed. I would be looking specifically at the extractor spring first.
Thanks again for the help!
That's an important distinction, as the malfunction was not a true doublefeed, as mentioned above and I should have made that more clear, apologies. One case was empty and didn't clear the feed path of the next round. Had it been a true DF I'd have looked at the mags instead of the BCGs.
I have a spare parts kit, so I'll swap out the spring in the BCM and see what happens. I was mostly confused about the difference in recoil, and I think that distracted me from troubleshooting properly.
This has been my main training/carbine class rifle so it's got some mileage on it, and I'm starting to see parts failure.
Wouldn't we be looking at a possible EJECTOR spring issue as opposed to the extractor?? Either of these are easy to quickly assess. With the bolt out of the gun, does an empty piece of brass "fling" off the bolt face when hooked under the extractor??
The 11.5's will wear stuff out quicker than a 14.5 or 16. More gas port erosion, gas ring/tube wear. The bolt takes more of a beating too if the gun is overpassed.
For sure, which is why it's important for people to actually articulate the issue. This would be fairly easy to troubleshoot. Personally I would approach it from a one-at-a-time method and replace the extractor spring first and then the ejector. This way you nail it down exactly and have a reference for the next malfunction.
Wouldn't we be looking at a possible EJECTOR spring issue as opposed to the extractor?? Either of these are easy to quickly assess. With the bolt out of the gun, does an empty piece of brass "fling" off the bolt face when hooked under the extractor??
FYI, I had the same issue and it ended up being the bcg. I had to get Pat Rogers involved as BCM dissmissed me. Eneded up being a bad batch of bcgs.
Interesting. What was the timeframe?
FYI, I had the same issue and it ended up being the bcg. I had to get Pat Rogers involved as BCM dissmissed me. Eneded up being a bad batch of bcgs.
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If you can feel it cycle slower with one BCG it is probably a gas issue.
Check the rings and the carrier key bolts.
I don’t want to drift this thread to far off, but I have had two new complete BCG’s from the same company that have had their carrier cam pin paths machined slightly out of spec where the pin *very noticeably dragged on the upper much more than normal when pulling back on the CH. I will just say brand wise they are a top tier and don’t get any better. I Put in a new BCM BCG and different brand than previous, and the excessive drag was gone. I also tried the other cam pin in the BCM bolt carrier and again, no drag. So to me it shows that any company can produce stuff out of spec and that gets by their QC program from time to time.
TomPenguin5145
12-20-18, 17:44
Way late to the thread here...but if I had enough rounds through my AR to wear out the gas tube...I just just "rebuild it" all. New tube, new gas rings, new extractor and new springs. These parts are super cheap. :-) Sorry. I know that prob didn't help. :-)
Way late to the thread here...but if I had enough rounds through my AR to wear out the gas tube...I just just "rebuild it" all. New tube, new gas rings, new extractor and new springs. These parts are super cheap. :-) Sorry. I know that prob didn't help. :-)
Gas tubes can wear prematurely for other reasons. Key misalignment could cause this. And I have had middy gas tube tips wear out in hundreds of rounds. Someone else here experienced the same. The outer diameter wore down and let lots of gas leak out into the rail area. Replaced it, and the gun came back to life.
Gas tubes can wear prematurely for other reasons. Key misalignment could cause this. And I have had middy gas tube tips wear out in hundreds of rounds. Someone else here experienced the same. The outer diameter wore down and let lots of gas leak out into the rail area. Replaced it, and the gun came back to life.
Do I need to consider the type of stainless steel they're made from? I've never heard anyone make a distinction between manufacturers of gas tubes.
There are only a couple actual manufacturers of gas tubes that I know of.
After installing a new gas tube verify alignment. This is done by removing the bolt from the carrier and inserting the carrier into the upper receiver. It should close smoothly without catching or dragging on the gas tube. If there is a stumble or an audible tick, adjust the gas tube until the tick is gone.
Do I need to consider the type of stainless steel they're made from? I've never heard anyone make a distinction between manufacturers of gas tubes.
No. Like Todd.K said, I've read they're mostly made by the same companies. For what ever reason, there appeared to be some crappy mid length tubes.
Way late to the thread here...but if I had enough rounds through my AR to wear out the gas tube...I just just "rebuild it" all. New tube, new gas rings, new extractor and new springs. These parts are super cheap. :-) Sorry. I know that prob didn't help. :-)
I tend to agree. A lot of folks live some distance from where they shoot, and many have to pay range fees, that plus the gas money kind of leans me toward making sure I solve the problem versus multiple range trips or rebuilding a part at the range.
Especially since, based on the OP's description, it is an issue confined to one BCG.
Check the key for leakage, make sure there is nothing obstructing the gas passage, use the gravity method to check the gas rings. Someplace during this process you should have looked at the extractor, if not, do so now, make sure it isn't chipped and is clean.
Then, here is my hillbilly way of checking ejectors: BCG placed horizontal in the padded vise, carrier key up, bolt extended. Take an empty case snap the rim under the extractor and press it firmly against the ejector - I use my thumbnail to hol it in place. Then I stand to the side,slide my thumb nail off the case and let it fling. With the bolt fully extended I find the cases generally hit the shop floor about five feet away. I 'developed' this method after reading an article on ejector tuning for service-rifle shooters and decided to try it out.
I think that mostly you'll find that if anything the ejector is slowed by being cruddy, not the spring sacking out. Generally a disassembly and cleaning will put you back in action. The OEM spring is pretty stout for the job - I've cut up to four coils off an ejector spring and had it still function - don't do this on anything but a rifle shot strictly for fun or competition.
All that being said, unless you want to get something that has been fondled by a Volcano Virgin, you can buy a bolt rebuild kit for under $20.00.
I think the extractor spring is definitely the culprit here. I compared the tensions with my finger, and the old bolt's extractor had much less resistance than the new PSA bolt. I'll take it to the range after new year's and check it out.
BCM extractor springs are very stout. There was a huge difference for me when I replaced a toolcraft spring with a BCM (both brand new). If the PSA feels like it has more spring pressure then it’s probably time to replace it.
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