View Full Version : 6920 Bolt Won't Lock Open
Short version of the problem: I can't lock the bolt back on my M4. I can't lock it back manually, and it doesn't lock open on an empty mag. What am I doing wrong?
Long version: my theory is that gun sellers increased stocks of guns and ammo in anticipation that we would all panic, again, after Hillary beat Trump. That didn't happen, so they were left with excess inventory. Colt started selling M4 Troopers, with the Centurion rail for a great price, so I bought one even though I didn't need it. Just couldn't resist.
Last week I started to worry that perhaps I had lubed the thing with fire clean, back when I somehow thought that was a good idea. Perhaps the rifle was all gummed up, so I cleaned it and greased it with Lubrikit. Now much of the time I can't lock the bolt open. SOS
That seems odd, are you getting full travel of the bolt catch? Is traveling freely or is it gummy or sticky? If you pull the rear pin and open up the rifle, how does the bolt catch look? Full travel rocking back and forth? Anything look broken?
The catch is now nicely lubricated and seems to move freely. I didn't notice anything that appeared to be broken, but I like your ideas and will compare it with another Colt this evening after work. Thanks
If you can't lock it manually, it could be broken. (the catch) That or the plunger/spring broke which is limiting travel of the catch.
Can you visually see the BCG can go back far enough to lock open? Could something be in the receiver extension?
If you can't lock it manually, it could be broken. (the catch) That or the plunger/spring broke which is limiting travel of the catch.
My first guess is going to be broken bolt catch. My actual first guess was operator error, but since we are talking about this board, I'll remove that from the equation.
Hammer_Man
09-08-22, 21:07
Did these problems come about after you disassembled and cleaned the gun?
Truly grateful for all helpful suggestions. The one questioning whether I was able to fully retract the bolt resonated with me, because I had studied the bolt catch for obvious defects several times. This led me to the answer-my LGS had installed a UTG Pro collapsible butt stock. In the wrong position it will actually block the rearward motion of the charging handle. I'm embarrassed, but at least the mystery is solved and the gun is essentially healthy.
Serious question-what's a reasonably priced, good quality collapsible butt stock? I'm sure a hundred meet this description but where would be a good place to start? Many thanks.
Beat Trash
09-09-22, 08:39
Serious question-what's a reasonably priced, good quality collapsible butt stock? I'm sure a hundred meet this description but where would be a good place to start? Many thanks.
My preferred stock is the MagPul MOE SL.
But I’d be OK with one of the stocks from B5 Systems.
Don’t pay a shop to install a butt stock/ as long as the Gunshop left the factory receiver extension alone, you can do it yourself.
Hammer_Man
09-09-22, 08:39
Vltor or Magpul. Glad you figured it out.
bamashooter
09-09-22, 09:29
Truly grateful for all helpful suggestions. The one questioning whether I was able to fully retract the bolt resonated with me, because I had studied the bolt catch for obvious defects several times. This led me to the answer-my LGS had installed a UTG Pro collapsible butt stock. In the wrong position it will actually block the rearward motion of the charging handle. I'm embarrassed, but at least the mystery is solved and the gun is essentially healthy.
Serious question-what's a reasonably priced, good quality collapsible butt stock? I'm sure a hundred meet this description but where would be a good place to start? Many thanks.
I too was thinking release/catch. LGS story is pathetic. Speaking of, how can the collapsible stock be in the "wrong position". Unless flawed or a matter of aesthetics, your UTG should be fine. As others have stated, never had an issue with any Magpul products. Decent choice of brands with assorted looks and features. I'd look around and then find reviews and user opinions on any given item.
My preferred stock is the MagPul MOE SL.
I have 2 of the MOE SL stocks and they've taken the lead as my favorite collapsible stock. Before that I would have said CTR.
the AR-15 Junkie
09-09-22, 10:29
I have 2 of the MOE SL stocks and they've taken the lead as my favorite collapsible stock. Before that I would have said CTR.
Agreed. Really like the SL stocks, SL Grips, just not the SL Handguards lol. I got rid of my CTRs.
Serious question-what's a reasonably priced, good quality collapsible butt stock? I'm sure a hundred meet this description but where would be a good place to start? Many thanks.
The price has come down on BCM's stocks. They're sub $60 dollars now. Not sure if everyone's prices are lower, but $58 or $56 for a bomb proof stock with a good rubber butt pad is nice!
There are a lot of good stocks out there, UTG aint one of them. Glad you ridded yourself of that piece. BCM, Magpul or Vltor should make you happy once again with your nice Colt.
PB
Bamashooter-the charging handle clears the butt stock when it is fully collapsed, and I believe when it is fully extended. Midway however, somewhat incredibly, it hits the uppermost portion of the butt stock. I typically don't use anything but fully extended or fully collapsed, so I was really scratching my head.
I like the BCM stock replacement idea, but I have a new rifle with one and the release lever to collapse the stock is so over sprung my girlfriend can even manipulate it, and she's no wimp. Unless I can figure out this problem I will likely go with the recommended Magpul SL. If I do, do you guys recommend the Mil spec or commercial version of the SL? Many thanks
It should be a MIL SPEC tube so get MIL SPEC. Commercial is rarely used and not with Colt.
PB
Rock Rivers use of Commercial tubes is a Sin.
MILSPEC all day long.
MILSPEC gives you a number of stock options, Commercial doesn’t.
BCM makes good stocks.
B5 makes good stocks.
Magpul makes loads of different stocks.
Vltor makes good stocks.
Just a reminder to anyone who posts about issues they are having. Without giving all the information (posting a pic helps), you probably won't get the info you need.
Lots of good advice on stocks above.
This is what I use in all my home brews.
https://uploads.tapatalk-cdn.com/20220909/f44e9c7d2a26d77b652242a8043df62c.jpg
DSG has complete Magpul kits in colors on sale. (RE, Spring, and buffer included)
Truly grateful for all helpful suggestions. The one questioning whether I was able to fully retract the bolt resonated with me, because I had studied the bolt catch for obvious defects several times. This led me to the answer-my LGS had installed a UTG Pro collapsible butt stock. In the wrong position it will actually block the rearward motion of the charging handle. I'm embarrassed, but at least the mystery is solved and the gun is essentially healthy.
Serious question-what's a reasonably priced, good quality collapsible butt stock? I'm sure a hundred meet this description but where would be a good place to start? Many thanks.
The first place to start is back at the gun shop that installed airsoft parts on your 6920 which rendered it inoperable. I would be he swapped out a lot more than that and you paid full retail.
titsonritz
09-09-22, 20:38
I have 2 of the MOE SL stocks and they've taken the lead as my favorite collapsible stock. Before that I would have said CTR.
Agreed. Really like the SL stocks, SL Grips, just not the SL Handguards lol. I got rid of my CTRs.
I wanted to like them, bought a couple of them, but ended up selling them off.
The original BCM is my go to stock especially if I'm looking for something lightweight and compact. I have found they work best for me using tall mounts which I gravitating toward. I also have a couple B5/LMT SOPMOD and a B5 Bravo. Like already stated, there are a ton of excellent stocks out there but UTG is one of them.
titsonritz
09-09-22, 20:52
Truly grateful for all helpful suggestions. The one questioning whether I was able to fully retract the bolt resonated with me, because I had studied the bolt catch for obvious defects several times. This led me to the answer-my LGS had installed a UTG Pro collapsible butt stock. In the wrong position it will actually block the rearward motion of the charging handle. I'm embarrassed, but at least the mystery is solved and the gun is essentially healthy.
Serious question-what's a reasonably priced, good quality collapsible butt stock? I'm sure a hundred meet this description but where would be a good place to start? Many thanks.
What exactly did you employ him to do?
titsonritz
09-09-22, 20:53
The first place to start is back at the gun shop that installed airsoft parts on your 6920 which rendered it inoperable. I would be he swapped out a lot more than that and you paid full retail.
^^^Right here.
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