LMT vs BCM BCG's (photographic comparison)

[CouchOperator]

This thread is simply to post the differences i have observed in my non-engineer just-a-guy-who-shoots eyes, regarding the physical differences in the LMT and BCM BCG's. These are unmodified, pulled directly from factory shipped guns.

Both will work plenty well for anybodys rifle. This isnt a VS thread, but a "make of it what you will" thread. The LMT BCG is out of a 2016 MRP DI 16" gun, and the BCM BCG is from a 16" standard barrel upper.

LMT will always be on the left. BCM will always be on the right for the photos to follow.

Starting with the bolt.

It appears both solve the issue of carbon displacement in different ways. LMT has a recessed channel directly behind the lugs, whereas BCM chose channels in line with the bore.



As far as the external portion of the extractor, BCM's channels are longer as well.



Side view of the extractors. LMT has an O-ring and what appears to be a slightly shorter spring (and if my eyes arent playing tricks on me, thicker body)
BCM uses no o-ring

[CouchOperator]

With the firing pin, it appears the LMT is slightly thicker in the rear. Whether this has any realworld difference, i cant comment on.



Both stakings look good, however LMT seems to have screws that fill the carrier in. BCM's look somewhat undersized for the holes.



On the gas key, it appears LMT has a chamfer at the forward portion of the key



BCM cam pin and LMT cam pin's are virtually identical, however there is a small circular marking on the BCM cam pin that is probably nothing, but is a difference i noticed




And lastly, LMT came as a semi auto carrier, whereas BCM is a "full auto" carrier.





If there is anything you are interested in that i missed, feel free to suggest.

[Devilmonkey89]

Inside of bolt carrier where the bolt rides.

Edit: machining of bolt face, machining of the little rails that the bcg rides on. Don't know the proper name of them.

[CouchOperator]

Inside of bolt carrier where the bolt rides.

On it. Gimme a few min

LMT



BCM.



Sorry for the terrible photos lol. BCM is definitely shinier.

Lmt left, bcm right. The mouths of the gas keys are also visibly cut differently

[CouchOperator]

As far as the bolt faces, the LMT on left only has the rounds on it fired from the factory. I will update it after my zero and function test this weekend. I do not currently have a high round cound LMT bolt, however the wear would be similar as the BCM bcg with whoknows how many thousands of rounds are on it.



Rails. LMT left, BCM right

[CouchOperator]

wow, thank you for the sharing man, I'm quite newb here, this is really interesting to know
//spammer tracking image deleted//

No worries dude. Im not an engineer so i cant comment on the effectiveness of the differences, however they have little minute differences i noticed. Either will be high quality and will serve the user well. I do not believe one to be better than the other. Just had some time to kill and doing a preflight check on the LMT before it gets ran this weekend, so i chose to snap some pics

[Dhena81]

I've heard it said before that the LMT bolt recess behind the lugs are for stress relief.

I've been running a LMT enhanced carrier with a standard bolt and that is a cool design also. One of the coolest features are the cam pin track is different which is supposed to slow the unlocking time and make extraction easier as a result. I could post some pics of the LMT enhanced carrier along side a BCM and a KAC BCG.

[CouchOperator]

I've heard it said before that the LMT bolt recess behind the lugs are for stress relief.

I've been running a LMT enhanced carrier with a standard bolt and that is a cool design also. One of the coolest features are the cam pin track is different which is supposed to slow the unlocking time and make extraction easier as a result. I could post some pics of the LMT enhanced carrier along side a BCM and a KAC BCG.

Closest thing i have to a KAC bcg is in my MWS, but finding an Sr25 bcg will be difficult. A friend has an SR15 upper. If i ever get an enhanced LMT bcg ill do a side by side

Regarding stress relief, i thought the two were connected. A place for extra carbon to go leads to less stress when the bolt is trying to lock.

Pics of your LMT enhanced and the KAC bcg's would be fantastic

[geoint]

Cool write up. I like it.

I have 5 BCM uppers all with BCM bcgs (haven't shot any of them yet lol) and I was pretty sure they would be good to go but I always appreciate hard facts over emotion or "well I hope it'll be good". I bought my BCMs due to their reputation and hearing hat your bcg has seen thousands of rounds and still looks like t does makes me happy.

Btw that's a well maintained weapon! Kudos

[CouchOperator]

Cool write up. I like it.

I have 5 BCM uppers all with BCM bcgs (haven't shot any of them yet lol) and I was pretty sure they would be good to go but I always appreciate hard facts over emotion or "well I hope it'll be good". I bought my BCMs due to their reputation and hearing hat your bcg has seen thousands of rounds and still looks like t does makes me happy.

Btw that's a well maintained weapon! Kudos

Thank you. Its one of the few times a year i take it apart and inspect parts and do some good cleaning lol. Your's will serve you well im sure.

[HooYah]

Does your LMT BCG have a MIM gas key?

[CouchOperator]

Does your LMT BCG have a MIM gas key?

Negative ghost rider. MIM gas keys have a circular mark between the screws on the top

[HooYah]

Negative ghost rider. MIM gas keys have a circular mark between the screws on the top

Solid copy. I wonder when LMT made the switch back to non MIM gas keys?

[CouchOperator]

Solid copy. I wonder when LMT made the switch back to non MIM gas keys?

I think that was only about a year. I think theyve stopped for the last 2 years. I was aware of that and its actually one of the first things i checked when i was out searching for an MRP lolol

[Dhena81]

In advance sorry for the crappy pics I just wanted to contribute a bit.

LMT-Enhanced left KAC right
LMT has a longer and more gradual cam pin cutout
KAC uses the standard path



Left to right LMT-E, KAC, BCM
LMT-E more gas ports a boss cut in the front and different rails
KAC has larger diameter gas ports than the BCM



BCM top KAC bottom
KAC has a different extractor and a smaller diameter cam shaft



KAC right has an E3 bolt



BCM left KAC right
KAC has a smaller cam pin and a different firing pin because of the smaller cam pin.