View Full Version : Need help diagnosing a problem with my rifle...
I took my new upper out for the first time today. Shot 60 rounds 5 rounds at a time just to get a feel for it and everything was fine. I loaded 20 rounds in a 30 round mag and that's when the problem started. It would fire one round and the bolt would get stuck open about 1/4" and it wouldn't extract. I had a hard time pulling the charging handle back to get it to extract. I fired 40 rounds like this and quit. I took the bolt apart and didn't see anything wrong with it or the extractor.
The rifle is a 14.5" LMT M4 upper with LaRue 9.0 and gasblock. I'm running a LMT standard M16 BCG with Crane O ring and a PRI Gas Buster charging handle. The lower is an LMT with 2 stage trigger and stock carbine spring/buffer. The mags were 2 D&H black teflon with gray Magpul followers and 1 Labelle gray teflon with brown Magpul follower.
Any ideas? Thanks!
BravoCompanyUSA
06-17-06, 13:24
I took my new upper out for the first time today. Shot 60 rounds 5 rounds at a time just to get a feel for it and everything was fine. I loaded 20 rounds in a 30 round mag and that's when the problem started. It would fire one round and the bolt would get stuck open about 1/4" and it wouldn't extract. I had a hard time pulling the charging handle back to get it to extract. I fired 40 rounds like this and quit. I took the bolt apart and didn't see anything wrong with it or the extractor.
The rifle is a 14.5" LMT M4 upper with LaRue 9.0 and gasblock. I'm running a LMT standard M16 BCG with Crane O ring and a PRI Gas Buster charging handle. The lower is an LMT with 2 stage trigger and stock carbine spring/buffer. The mags were 2 D&H black teflon with gray Magpul followers and 1 Labelle gray teflon with brown Magpul follower.
Any ideas? Thanks!
Basically it ran ok for a short bit, and then it pretty much stopped cycling.
Assuming the bolt carrier group can travel freely in the upper and works to hand cycle and eject rounds...
My first guess, would be to look at the gas system.
If your firing weapon and the bolt does not move to the rear, you may have lost most/all pressure. Take a peak at the gas block to insure it did not come loose or rotate well off center. Also look at the gas tube, to insure the roll pin is securing it.
I would also look closely at the gas key on the carrier - however I have never personally seen a LMT carrier gas key get loose.
Contact the company that set up the upper for you, it should be an easy fix.
Paul gave you some good ideas. I would make sure that the bolt and carrier is properly lubed and try some different mags and ammo.
I would load one round into a mag and see if there is enough pressure to lock the bolt back.
C4
The guys above covered it. Check gas system and change mags. See if problem returns.
Thanks for the replies. The ammo is Winchester Q3131.
Thanks for the replies. The ammo is Winchester Q3131.
Could be a bad batch (not likely though).
C4
I just looked at my rifle again. The gasblock doesn't seem to be loose. It does look like there is an 1/8" gap between the gasblock and the step up in the barrel. Is this normal?
http://img220.imageshack.us/img220/6763/dscn06760nm.jpg
Is the gas block pinned on or bolted on? If it's bolted on I suspect it could have moved while still being somewhat tight.
Do like Grant said and fire a round and see if the bolt locks back. At least then we'd have a good starting point but right now the gas block would be my #1 suspect.
M4arc, I'm not sure about the gasblock. I'll check with the person that built my upper.
K.L. Davis
06-17-06, 16:42
RHR
I just noticed your post... sounds like the advice you have gotten is good.
A lot of folks do not realize that the gas block (and everything else) tries to move forward under the recoil of the rifle, it only takes a little bit to block off enough of the gas port enough to effect the function of the rifle.
Rifles that use a set screw mounted gas block *should* have the barrel machined 180 degrees opposite of the gas port, for the rear set screw to recess into -- this ensures alignment and helps prevent movement of the gas block.
BravoCompanyUSA
06-17-06, 18:27
I just looked at my rifle again. The gasblock doesn't seem to be loose. It does look like there is an 1/8" gap between the gasblock and the step up in the barrel. Is this normal?
http://img220.imageshack.us/img220/6763/dscn06760nm.jpg
Generally speaking, there should be a slight gap between the gas block and the shoulder of the barrel, for the ports to line up correctly. The gap represents where the handguard cap would have been if you were not running a free float. (Some manufacturers may do it differently, and I am not sure exactly how LT does it).
I can't be sure from the picture, but it looks like the gas block may be sitting a bit too far forward - if so, that would shut down (or greatly reduce) the gas system.
If that is a LT block, then it is to far forward.
Remove the handguard and reposition the block. Be sure to was red loctite on the set screws. I've built several rifles using LaRue gas blocks, none have sit that far forward.
ETA: I reread your first post. That block is not back far enough. There should be a gap of 3/32" to 1/8" tops. Right now you are cutting off your gas.
I want to add that the D&H mags are dated 11-05. I remember reading a thread on the "other" forum about people having problems with that date.
Does anyone know if that was true?
BravoCompanyUSA
06-17-06, 20:22
I want to add that the D&H mags are dated 11-05. I remember reading a thread on the "other" forum about people having problems with that date.
Does anyone know if that was true?
That will have nothing to do with failure to cycle.
Mag issues are only related to feeding issues. By your description above - your mags are good to go.
it is a gas issue, follow the advice and get the block installed correctly and you should be squared away
Your gas block is to far forward. That is your problem.
C4
Ok, I did what Grant suggested. Put 1 round in the mag and shot it. It locked the bolt back on the empty mag.
Ok, I did what Grant suggested. Put 1 round in the mag and shot it. It locked the bolt back on the empty mag.
Did you only try this once? Or did you test this multiple times?
How did it extract when you ran this test? When you were having the problems the other day was the empty case still in the upper or was it still in the chamber?
Did the FTe look like it was trying to chamber a new round while the spent case was in the way?
Ok, I did what Grant suggested. Put 1 round in the mag and shot it. It locked the bolt back on the empty mag.
Did you move the gas block back?
C4
I would have to concure that the gas bolck is the issue. However, if the weapon is cycling and locking back onthe one round test, that could mean its something else. Not sure what at the moment though.....
You said you are shooting Q3131 in it now. Has there ever been any Wolf shot through it? Reason I ask is, I have had to work ona couple of AR's at work recently that the owners had been shooting Wolf through and then switched to brass cased ammo. The Wolf would run fine, but the brass cased rounds would stick in the chamber and fail to extract after just a few rounds were through the gun and the chamber heated up.
I only tried once because I was in my Dads backyard.I didn't want to shoot much because of his neighborhood. That's not much of a test but that's all I could do today. Yesterday the empty case was still in the chamber and to get it out I really had to yank on the charging handle. Today it extracted fine on the one round.
I didn't move the gasblock. How hard is it to remove/replace a LaRue rail and gasblock?
Hasn't been any Wolf shot through it.
I'm going to have to go with the gas block being the problem (unless for some odd reason the carrier key is not fully tight, though as mentioned this is unlikely) or the chamber is oversized/out of spec.
For your first session where you experienced the problem, would you say the weapon was lubed sparingly, moderately or liberally? What lube was used? How much time elapsed between when it was lubed and when you shot it?
I only tried once because I was in my Dads backyard.I didn't want to shoot much because of his neighborhood. That's not much of a test but that's all I could do today. Yesterday the empty case was still in the chamber and to get it out I really had to yank on the charging handle. Today it extracted fine on the one round.
I didn't move the gasblock. How hard is it to remove/replace a LaRue rail and gasblock?
Hasn't been any Wolf shot through it.
It is easy. Remove the rail and pull it over the GB. Loosen the screws securing the GB and move it back till it hits the shoulder. Remove the screws and clean the old loctite off of them and apply some more before screwing them back in.
Install the rail.
C4
One of the great design features of the LaRue gas block is that the rear allen hole is directly in line (and around the same size?) as the block's gas hole. Thus, aligning the barrel's gas port with the gas block is easy- Just slide the block on upside down, and look through the rear allen hole.
http://i6.tinypic.com/14uwbjc.jpg
Its really hard to shoot macro photos with my cheap phone, but you can at least see the port position in #1, where the block was pushed all the way back. There's still enough space for slight adjustment without blocking the port.
http://i6.tinypic.com/14vh2s1.jpg
In #2, I pulled the block forward enough so the back edge of the barrel port is even with the edge of the block's hole. That's the maximum space that should be allowed for a handguard cap, if needed.
http://i5.tinypic.com/14vh4xx.jpg
In #3, the barrel's port is already starting to get covered by the block. In your photo, it looks like the amount of space here, or perhaps even more.
http://i6.tinypic.com/14vh5lg.jpg
My only other guess is that the loose block may have shifted R/L enough to cause binding on the gas tube where the tube meets the gas key. Maybe it is loose enough to have moved back into the correct position before your 1-shot test?
I just took the rail off like Grant said. The gasblock was loose. I took the screws out wiped them off and put some Loctite on them. I put the gasblock against the shoulder, hopefully it's not back too far.
Thanks to everyone for your help.:D
Excellent post Kisara.
RHR glad you found the problem.
I just took the rail off like Grant said. The gasblock was loose. I took the screws out wiped them off and put some Loctite on them. I put the gasblock against the shoulder, hopefully it's not back too far.
Thanks to everyone for your help.:D
Did you use loctite the first time you installed the GB?
C4
I didn't build the upper. I had someone build it because the Phantom had to be pinned and welded.
I didn't build the upper. I had someone build it because the Phantom had to pinned and welded.
Hmm, well if you PAID for them to build your upper, I would go back and have a little discussion with them!
C4
I let him know the gasblock was loose. I'm interested to get his reply.
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