View Full Version : problem with bolt carrier
Setup: brand new Noveske 10.5" barrel, CMT upper, CMT bolt, semi LMT carrier, H2 buffer, and AAC M4-1000. LMT lower w/ SOPMOD. After the last round in the mag is shot the bolt carrier will lock back, however it is locked back so tightly that I have to really slam the bolt release. Sometimes that won't even work, even the charging handle won't release. Other times when it doesn't lock so tightly, I'll hit the bolt release and it barely rides forward and it won't chamber a round.
I experienced similar problems with a Bushmaster upper on the same lower, it wouldn't put a round into the chamber. Something makes me think it's the carrier. What say you?
ETA: as far as I know - I'm using quality USGI mags w/ green or magpul followers.
I saw a similar situation recently with a .22 conversion kit in an AR. The OEM charging handle (Colt) had been replaced with a PRI gas-buster charging handle, and it was binding (slightly oversized) & causing similar symptoms.
Is your charging handle OEM? Try changing it out, if you have a spare.
Hope this helps. Good luck.
As far as I can remember it is a Bushmaster - I've just had it around from a previous rifle. I'll try switching it out, anything is worth a shot. Thanks.
Bill Alexander
04-28-07, 12:59
The sytem you describe indicates that the bolt catch is holding the bolt assembly under more tension than just the spring. The whole carrier assembly should be able to run back about 3/8" behind the bolt catch which should then move easily on the tiny spring under it. Equally the carrier assembly should move freely on the upper bore.
Good advice to check out the charging handle but something in that assembly is seriously sticking. Could be the cam path or the alignment of the upper and lower.
Bill Alexander
Does the same problem occur when you have the bolt locked back without an empty magazine inserted?
Doe the Bolt catch stick with the bolt removed or does it move freely?
I agree with Bill. There might be something binding up your BCG.
Generally, if you cannot strip a round off of a fully loaded mag it is because your buffer spring is wore out or the lips on your mag are holding the rounds too tightly. In this case, it might be something else.
C4
Does the same problem occur when you have the bolt locked back without an empty magazine inserted?
Doe the Bolt catch stick with the bolt removed or does it move freely?
With an empty mag inserted it seems to work just fine, and also the bolt catch stick moves freely w/ the bolt removed.
Okay,
What I was getting at, was; if you lock the bolt back without a mag in and hit the bolt catch, does it release easy?
Kind of an update - went over to another AR shooter's place to look for the problem. We narrowed it down to a weak buffer spring. His spring was about 1.5" longer than mine. We took a loaded mag and tried to chamber it with my buffer spring, no dice - it wouldn't feed. Put his buffer spring in my AR and it chambered just fine. His spring felt much more stiff.
Now my question is, where should I go and what kind of spring should I get. My spring is the one that came w/ the LMT lower.
Robb Jensen
04-28-07, 22:38
This is why there is a spec. for proper length of buffer springs.
Kind of an update - went over to another AR shooter's place to look for the problem. We narrowed it down to a weak buffer spring. His spring was about 1.5" longer than mine. We took a loaded mag and tried to chamber it with my buffer spring, no dice - it wouldn't feed. Put his buffer spring in my AR and it chambered just fine. His spring felt much more stiff.
Now my question is, where should I go and what kind of spring should I get. My spring is the one that came w/ the LMT lower.
Most of your standard SS spring have most of their useful life already spent (even though they have never been used). This is why we see NEW AR's that exhibit the problem you had.
I personally use CS springs and prefer the ones made by ISMI as they are shot peened, stress relieved and guranteed for a year.
C4
Grant -
Do you sell CS springs?
Grant -
Do you sell CS springs?
Yes, I sell the ISMI's (which are under ISMI on my web site).
C4
Congrats on your trouble shooting. e used to change M60 drive springs after every class as they would measure short on inspection. Same with handguns too, you have to check them regularly.
Glad you found the fix.
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