Problem with LMT upper

[gjj]

I just bought a new 16" M4 LMT upper from BCM. I ordered the auto carrier BCM BCG. The lower is using an H2 buffer.

I am having problems with the gun not locking back when empty. The ammo is Remington UMC 55 grain ammo. The mags are several D&H, Bushmaster, Cooper. I am running the gun pretty wet. Lubrication does not seem to be the cause.

I had a couple instances where the bolt closed on an empty chamber and it took significant force to retract the bolt with the charging handle.

Any ideas on the cause?

The one thing I have noticed is that the bolt does not move as easily back and forth in the carrier as my stag BCGs. It is very stiff. In my mind stiffer than it needs to be.

I wanted to post this in advance of calling Bravo Company on Monday to get ideas. I am not worried. Bravo has treated me very well and they probably have some ideas for me to try.

[Robb Jensen]

I just bought a new 16" M4 LMT upper from BCM. I ordered the auto carrier BCM BCG. The lower is using an H2 buffer.

I am having problems with the gun not locking back when empty. The ammo is Remington UMC 55 grain ammo. The mags are several D&H, Bushmaster, Cooper. I am running the gun pretty wet. Lubrication does not seem to be the cause.

I had a couple instances where the bolt closed on an empty chamber and it took significant force to retract the bolt with the charging handle.

Any ideas on the cause?

The one thing I have noticed is that the bolt does not move as easily back and forth in the carrier as my stag BCGs. It is very stiff. In my mind stiffer than it needs to be.

I wanted to post this in advance of calling Bravo Company on Monday to get ideas. I am not worried. Bravo has treated me very well and they probably have some ideas for me to try.

In my professional opinion an H2 used with an LMT stock upper with Remington ammo is just asking for short-stroking. Remington ammo is very weak and LMTs work well with CAR buffers with .223 pressure ammo. If using 5.56mm NATO pressure ammo a H buffer can be used

To very this contact LMT.

[M4arc]

I believe GotM4 gave you a good troubleshooting tip; if hotter ammo and a H buffer don't do the trick please contact LMT directly.

GotM4 is not logged on now so I can't discuss this with but I'm going to re-open this thread so that others may weight in and offer their advice. If it goes the direction he thought it was going in and I look like a fool I won't be a happy camper.

BTW, I did move your other thread to trash because threads like that aren't necessary here. If you have a question please contact one of the mods or staff via PM.

[C4IGrant]

LMT, Colt BCM (for instance) all use .063 gas ports. Couple that gas port size with weak ammo and an H2 buffer and you CAN get short stroking. Buy an H or carbine buffer in it or cut a coil or two off your buffer spring.



C4

[gjj]

Thanks. As an alternative, could I use an A2 stock and rifle buffer and expect better performance? Would the rifle buffer in an A2 stock be more forgiving?

Note: This "problem" is not LMT's fault. I was the one who chose the components. I just want to do some research and explore all options before I call so I don't waste their time.

[ST911]

Echo the above. You have heavy components and marginal (at best) ammo. Stacking tolerances and short stroking.

[Blackdeath13]

I also have had the same issues with a BCM, semi bolt group, standard spring in a Bushy 20". Very stiff.
Will try hotter reloads and report.

[C4IGrant]

Thanks. As an alternative, could I use an A2 stock and rifle buffer and expect better performance? Would the rifle buffer in an A2 stock be more forgiving?

Note: This "problem" is not LMT's fault. I was the one who chose the components. I just want to do some research and explore all options before I call so I don't waste their time.

I don't know why you would us an A2 stock and rifle buffer (as A2 stock suck).

I am not sure what "performance" you are looking for. If you want zero recoil, then get a ciener kit and shoot .22's through your gun.


C4