LMT E-Carrier/BCM 11.5" Barrel; BCG Wear...

[Shooterman017]

Good evening all,

Looking for guidance/input on wear exhibited on an 11.5" BCM-barreled SBR using an LMT E-Carrier. Broke the gun apart to do a little cleaning earlier, figured I would grab a couple pictures while it was opened up. I have been using this gun in this configuration for more than a year now (have not logged an exact round count, but it is at least a couple thousand rounds, mostly XM193 or comparable pressure rounds), and while it is mostly in factory condition, I have changed the original KMR 10 for a KMR 7 and installed a PRI front sight gas block. I do not believe these articles have any bearing on the wear patterns that have developed on this BCG. Notable parts I would think are relevant include:

• BCM 11.5" upper: Factory installed barrel/torqued barrel nut in a BCM4 upper. I have not touched/altered the specific torque of this article, nor removed the barrel from the upper.
• LMT Full-Auto E-Carrier/BCM bolt: If memory serves this E-Carrier is the latest generation (purchased just over a year ago from LMT). The bolt comes from BCM (a complete BCG); it was purchased at the same time as the upper in the summer of 2014. Pulled the bolt/guts from the BCM carrier and dropped everything into the E-Carrier when I switched over to it.
• Vltor A5 System: I built the lower with a BCM A5 receiver extension and initially ran a standard rifle spring and A5-0 buffer (mainly with the original BCG). Still running the standard spring, now using an A5-H3 buffer since installing the LMT E-Carrier.

This upper is run >99% of the time suppressed (an Allen Engineering AEM3 up front). About the only time I have not run this gun suppressed was when initially testing buffer weights and using weaker ammo to check function. Now, the wear that I have noticed over time is in two distinct places. The cam pin has a distinct line of wear (outlined in the image below in red), where it rides against the outboard portion of the cam path. It has worn the finish of the pin off (it is polished essentially, but hard to discern due to lighting) and you can feel where the wear starts and stops with your fingernail. The nose of the carrier is showing distinct wear marks from the barrel extension interacting with it (the wear pattern is easily discernible in the image).





For reference, I am using BCM bolts and carrier parts in two other rifles; one is a MK12 that is also run suppressed full time (with a BCM carrier, the original from this 11.5" upper), the other being a MK18 CQBR with 10.5" barrel, unsuppressed full time (using another LMT FA E-Carrier, latest gen as well). The MK12 does not show nearly as exaggerated wear (looks like it should, no big deal), but it also does not have as high of a round count yet. The E-Carrier/components in the CQBR are starting to show wear somewhat similar to the 11.5", but it has a drastically lower round count so I can't make an honest comparison. I also remember it being mentioned here by other members that the E-Carrier may wear from interaction with the barrel extension, however I cannot find the posts or recall if it was a serious concern or to be expected...or if it is dependent on the barrel/extension. I am especially interested to see if such a wear pattern is unique to one brand of barrel of if it is universal and just dependent on round count/use.

For what it's worth, I am a believer of the E-Carrier/A5 system. It made a world of difference on the 11.5" gun going from standard BCG/lighter buffer to E-Carrier/heavier buffer. This carbine has not failed once set up as it is. Period. I have not shot any components on my carbines to a point of potentially needing replacement, save for an old mil-spec trigger that had a sticking disconnector and would double, and old gas rings on a used BCG...cam pins are cheap, replacing one isn't a big deal...any insight and experiences would be appreciated though with regards to the carrier...

Sort of on topic: I am strongly considering building another 11.5" upper using a Sionics Reduced Gas Port barrel, since this has essentially been a dedicated-suppressed carbine. Anybody with BCG component wear input on this setup and if it extends component life by any appreciable measure would be interesting to hear as well.

[sinister]

Normal wear.

Shoot it. If wear on the cam pin bothers you get one that's been hard-chromed or nitrided.

No machine lasts forever.

[tom12.7]

When you say the outboard portion of the cam path, you are referring to the ejection port side?
Doesn't really matter too much on that for the cam pins, some LMT enhanced carriers do wear cam pins more than others. Even when you end up with a LMT enhanced carrier that does this more than others, the angled edge normally smooths out with use. It takes a lot of material removed from that location to hurt function. If you are concerned about that, just pick up some LMT or Colt cam pins.
As far as the contact surface between that carrier and the BE, that can be an issue. Not all BEs play well with the extended portion on the LMT enhanced carrier. Probably the easiest and cheapest way to check this is to buy a strip of plastigauge, place it on the flat face of the carrier without the bolt installed and check the fit to the BE. If it doesn't smash flat, you have parts that do not work together as well as they should and you have decisions to make. If it does smash flat, keep your parts and keep on shooting.

[BufordTJustice]

Normal wear.

Shoot it. If wear on the cam pin bothers you get one that's been hard-chromed or nitrided.

No machine lasts forever.

Agreed. A V7 Nitrided cam pin or Lantac Domed cam pin can be had if the wear bothers you. I usually put a dab of grease on the cam pin and smear it around with my fingertips before assembling into carrier and bolt body. I then will squirt a nice dollop of lube into the cam pin track after assembly of the BCG, bu before installation into the upper. My V7 and my Lantac cam pins show virtually no wear in their LMT e-carriers.

But, as Sinister said, this is truly a non-issue.

[Shooterman017]

If wear on the cam pin bothers you get one that's been hard-chromed or nitrided.

No machine lasts forever.

A V7 Nitrided cam pin or Lantac Domed cam pin can be had if the wear bothers you. I usually put a dab of grease on the cam pin and smear it around with my fingertips before assembling into carrier and bolt body. I then will squirt a nice dollop of lube into the cam pin track after assembly of the BCG, but before installation into the upper. My V7 and my Lantac cam pins show virtually no wear in their LMT e-carriers.

Wish I had paid more attention to the round count for the sake of a statistic..."no machine lasts forever" is definite truth. Typically I will do the same thing with the cam pin/track as well when cleaning or before a good range session. I'll be checking out V7...need an excuse to spend money with them, might have found it. Good stuff guys. Thanks.

As far as the contact surface between that carrier and the BE, that can be an issue. Not all BEs play well with the extended portion on the LMT enhanced carrier. Probably the easiest and cheapest way to check this is to buy a strip of plastigauge, place it on the flat face of the carrier without the bolt installed and check the fit to the BE. If it doesn't smash flat, you have parts that do not work together as well as they should and you have decisions to make. If it does smash flat, keep your parts and keep on shooting.

I will certainly be giving this a shot. Thank you very much...will follow up with results.