So I’ve been reading this forum for some time and absorbing as much knowledge as I can. Recently completed a new build that I felt would be rock solid, but so far things aren’t going so well. This is my first carbine length gas system build, so I’m hoping someone can help me troubleshoot.
Not sure if it was necessary, but when I received the upper and BCG, I cleaned them well and lubricated the BCG with Slip 2000 EWL. The BCG originally had a rather heavy coat of grease on the firing pin, cam pin, and bolt.
After cleaning and function check I took her to the range - immediately had problems starting with the first round. The first round fired fine, but had a FTE caused by a broken case. IIRC, ammo was Winchester white box 5.56 NATO. After clearing the case out with a cleaning rod I had a failure to go into battery caused by a part from the broken case getting stuck ahead of the bolt. OK, I can deal with that… quick fix.
After that, things did get better, but I’m not convinced it’s running well yet. I proceeded to shot various ammo including Wally World Federal 223, American Eagle 223, and Wolf 5.56. I did have a FTF, but for the most part it ran smooth.
Here are my questions:
[ol]
[li]Do I need to break this thing in? Should I shoot another 100-200 rounds before changing anything?
[/li][li]I have a standard carbine buffer in it, should I be running an H2 buffer?
[/li][li]Any other suggestions?
[/li][/ol]
That optic is preventing the weapon from functioning properly…
…ok… just kidding. Honestly, I usually won’t call a fighting weapon reliable until it can cycle 700 rounds without a malf. Just finished up a BCM/LMT build and had serious issues at first. Don’t sweat it. Buy a REGULAR H buffer… not some tungsten kryptonite arctic hybrid garbage then grab another case (of ammo) and run it. Use that ewl liberally… my ARs drip with the stuff. Nice build. Let us in on a range report and how the psa lpk holds up. Also… ditch the optic then grab a good white light and a sling.
Run a few hundred rounds of full power 5.56mm through it.
Most of the ammo you described using is underpowered.
I’m not aware of Wolf manufacturing 5.56mm ammo.
I’m also not aware of the gas port of an LMT upper.
If the upper is overgassed, the easiest, (and cheapest), thing to do would be to switch out to a heavier buffer.
When you cycle the action by hand is it rough/gritty feeling or any areas of high resistance? Sometimes on a brand new gun things can be a little rough out of the box, and cycling by hand (as much as you can) or just shooting it will solve those types of issues.
Also if you pull the trigger on an empty chamber, and then pull the CH backwards does it feel gritty? When you do this do it slowly, and you’ll feel the trigger being reset. Sometimes there can be excessive drag on the BCG from the trigger.
Just do a general look over of the gun and see if there are any parts yet that seem excessively worn for the amount of rounds you have through the gun. Make sure your your recoil spring is good and things like that.
The grease is a type of cosmoline which is a long term rust preventative so if the rifle sits on a box for a year the new owner doesn’t find a rusted out POS awaiting him. Make sure all of that stuff is out of the gun including the chamber and bore. That stuff is very tacky and can really mess up an AR.
No O-ring under the extractor. Don’t know much about that o-ring on BCM BCG, but I think it’s to help with extraction/ejection on SBRs? I assume it should not be installed on 16" carbine length gas system?
I went ahead and ordered a Colt H2 Buffer from Brownell’s. For some reason, they don’t carry a quality H Buffer… or at least I couldn’t find one online.
H2 should be ok assuming there are no other problems
Good news is you can make two H buffers from your Carbine and H2 buffer if you want.
Just remove the roll pin and set them up with 1 Tungsten and 2 steel weights
I would say you had one bad round, that caused an issue with another round/cycle.
The random FTF does seem odd.
If you can fire another 500+ rounds without issue I think your good
Yes , I saw that BC had them, but had already started an order with Brownells. I actually went ahead and ordered an LMT H buffer from VT Supply. They owed me free shipping on an item.
I’ll report my finding after its received and run. I think I’m going to run it with at least a hundred more rounds as is just to see what happens.
I didn’t have any factory 5.56 rounds, but shot bunch of reloads (LC brass, 69gr SMK, F205M, 25.0gr Reloder 15 as well as LC brass, 62gr FMJ, Rem7.5, 25.0gr TAC). Also shot more 223 cheap stuff including wally world Remington 223 Rem (green/white box), American Eagle 223, Wolf steel case 223, basically anything I could find laying around…
Overall I shot about 100 more rounds. I shot about 30-40 with the original “cheap” buffer and then changed out the buffer with a new LMT H Buffer. Only malfunction was a failure to hold the bolt back on an empty PMAG.
Here’s a group I shot with the aforementioned 69gr SMK reloads. Shooting was done at night on a lighted range for a front sandbag for support:
Not too shabby for a 16" carbine at night with irons and a crappy RDS.
Getting closer to being broken in… Now out to the range for some more breaking in.
It looks like you’re on your way to smooth sailing. I would be surprised if the LMT is overgassed. On my latest, greatest build, I initially had problems and switched to a carbine buffer for about 300 rounds. As it got broken in and everything settled I went back to the “H” buffer and it has to date been 100% for the last 1500 rounds. These were mostly Federal 5.56. After I felt confident I added some variables into the mix ammo wise and found it was still 100%. This included Black Hills 68 and 69 grain BTHP, 193 and 855, and even 3 mags of Wolf. I won’t go into manufacturers but the barrel is a 14.5 mid length and to date my favorite and I’m looking to buy another for my next build. Very accurate.
I have LMT 14.5 with a BCM BCG and I never had a FTF. I use federal XM855, M193, PMC 556, Vintage PMC from the 90s, and Federal 223 black box with a standard buffer. Switched to a BCM H Buffer and spring. Still no problem.
OK, now that this thing is running well I’m going to sell it. I know… I’m nuts, but I have been wanting a BCM 16" LW Middy for months now and I finally go my hands on one. Showed up today… Yippie!!!
Crazy ride, but in late September when I was finally getting ready to order it went out of stock the morning I was going to place my order. This is after being in stock for about 2 weeks. Then it went out of stock, then back in stock and I finally said screw it… I’m ordering one.
Anyway, I’m going to put this LMT upper, and maybe the whole rifle up for sale. I haven’t decided which route to go. Before I started this process I had two lowers waiting for uppers, so either way I’ll be GTG.
Thanks. From here I plan to add an Aimpoint T1 and put a “lighter” light up front.
Long story, but the short version is I REALLY wanted a mid-length LW setup and when I had a hard time trying to get on I decided to try the LMT carbine length setup. The 16" carbine format just didn’t work for me… just felt too short in the handguard and the recoil felt harsher.
So, when I found the BCM LW back it stock I went ahead and pulled the trigger (no pun intended). It really didn’t have anything to do with giving the LMT a chance from a reliability perspective. I wound up putting about 300 rounds through the LMT and the last few hundred rounds were very smooth with no issues. By that time the LMT upper and BCM BCG felt like they were getting along just fine together.
I normally shoot about 100 rounds for a “carbine” range trip.
