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Posted: 3/10/2026 11:44:26 AM EDT
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Is it a precious snowflake that only reliably shoots green-tip? Or is my barrel gas port drilled too small? Or what? I've tried different buffer springs (LMT and G$), and different buffer weights (Carbine, H, H2 and H3), with different types of ammunition (Hornady and Igman 223, and reman M193 556). No combination seems to work reliably. I've got the 12.5" barrel, and the advanced bolt with no gas rings, running unsuppressed on the N plug setting. |
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I just had to send a new MARS-H lower back to them because the pivot pin detent hole was out of position and I could not retract my pivot pin enough out of the channel to get my upper to close on the lower. Would not be surprised in the slightest if something is out of spec. I would contact them and try to send it back for review. LMT is quickly gaining a reputation... Learning Machining Together Let Mistakes Proliferate Loose Machining Tolerances etc... |
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Mine MRP closes on field gage 1.4696 but will not close on 5.56 nato max 1.4736. Not sure if I should send it back. This only rifle in my extensive collection of various types of rifles that closes on field gage. My older MRP from 10 years ago will close on go 1.4636 but not on no go 1.4666 |
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Originally Posted By BringbacktheCrusades: I would contact them and try to send it back for review. They gave me a line of bull about "We [...] only recommend full power 5.56 ammunition through our piston guns, as opposed to .223." I know, I know, but can we stop pretending there's actually a significant difference between these chamberings when we're talking about rifles built in the 21st century? They're trying to tell me it can't shoot Hornady TAP Police ammo, when a bargain basement RRA (and every other rifle I've ever tried it in) runs like a sewing machine on it? Not with any of the four buffer weights?! |
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I had the LMT Estonian reference rifle that I wanted to like but one of the biggest reasons I sold it was because it was so magazine/ammo dependent. I could not get it to work with any aluminum GI 20 rounders and I could get it to work with a metal mag but only if I shot IMI or Winchester M193 at the least but anything else I shot would not cycle reliably. I talked to LMT about it when I had the issue and they simply recommended I use the Gen3 PMAGs with full powered 5.56 rounds and it appears in that regard it has worked quite well but I can see that depending on ammo it might not lock back sometimes. I really wanted to like that rifle and I got a lot of rounds behind it until I eventually just sold it out of disappointment. |
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Maybe my problem is that I have Estonian contract barrels. I have so many rifles, I don't want to keep anything that's too finicky. I gave away dozens of Gen1 PMAGS because one of my ARs (which happened to have a registered full-auto receiver) didn't like them. I have a LOT of ammo that I bought at much lower prices than can be had today, if LMT won't address the cycling issue, I will abandon their piston platform entirely and declare HK to be the king of the pistons. |
Joined:
Dec 2024
Posts:
1261
EE: 100% (3)
VA, USA
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Originally Posted By LFOD1776: Is it a precious snowflake that only reliably shoots green-tip? Or is my barrel gas port drilled too small? Or what? I've tried different buffer springs (LMT and G$), and different buffer weights (Carbine, H, H2 and H3), with different types of ammunition (Hornady and Igman 223, and reman M193 556). No combination seems to work reliably. I've got the 12.5" barrel, and the advanced bolt with no gas rings, running unsuppressed on the N plug setting. Ive fired everything in mine... what malfunction are you actually seeing. aslo, the pistol is a 12 inch barrel, the specwar is 12.5. |
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Originally Posted By LFOD1776: It doesn't reliably strip and chamber the next round. Originally Posted By LFOD1776: Originally Posted By ShaggyNuckles: Ive fired everything in mine... what malfunction are you actually seeing. aslo, the pistol is a 12 inch barrel, the specwar is 12.5. It doesn't reliably strip and chamber the next round. Stupid question… But have you checked the pads on the bottom of the upper to see if the fitment is loose enough not to bind your bcg? I’d forgotten about this last time I got a new MRP upper but there’s small pads behind the pivot pin hole on your upper receiver it’s meant to be filed down to ensure a tight fit. It caused my 12” piston to have problems like you described. After I filed the pads down everything was fine. Here’s an instruction video from LMT on it for reference.  Fitting an LMT MRP Upper Receiver |
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Oh wow, I didn't even know about this! I went with the more invasive fix of selling the piston barrels and carriers in the EE, and buying new SPECWAR barrels and DI bolt carriers. Now my rifles are working great! I wish LMT sold a nickel-plated enhanced DI carrier, but otherwise I'm back in business, albeit with gassy uppers. I'm considering getting a flow-through silencer to deal with that. I'm also planning on trying out the new ARAD piston system when they start selling the 11" SBR version. |
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Originally Posted By LFOD1776: Oh wow, I didn't even know about this! I went with the more invasive fix of selling the piston barrels and carriers in the EE, and buying new SPECWAR barrels and DI bolt carriers. Now my rifles are working great! I wish LMT sold a nickel-plated enhanced DI carrier, but otherwise I'm back in business, albeit with gassy uppers. I'm considering getting a flow-through silencer to deal with that. I'm also planning on trying out the new ARAD piston system when they start selling the 11" SBR version. Yeah I had forgotten about it last time I had to deal with it and got really mad… Then I called and they explained it to me and I felt like a bonehead. It isn’t a LMT carrier but Centurion makes a sand cutter hard chrome carrier that’s really nice. KAK also has some interesting BCGs that are chrome with different enhancements. Leightner Wise rifle co has an enhanced carrier with improved cam pin geometry that’s supposed to really improve cycling from what I’ve read as well. I really like the LMT piston system but I have DI stuff from them too. Whatever piston you run I recommend also a buffer tube with a ramp that extends under the tail of the carrier. POF and PWS both make them, Aero precision had a really nice one that was my favorite but I don’t know their manufacturing situation right now given their business problems recently. |
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Originally Posted By Nate762: Stupid question… But have you checked the pads on the bottom of the upper to see if the fitment is loose enough not to bind your bcg? I’d forgotten about this last time I got a new MRP upper but there’s small pads behind the pivot pin hole on your upper receiver it’s meant to be filed down to ensure a tight fit. It caused my 12” piston to have problems like you described. After I filed the pads down everything was fine. Here’s an instruction video from LMT on it for reference.  https://www.youtube.com/watch?v=Cxs-s8fLdt4I had no idea I have a LMT that jams a couple times on every mag. Thanks for the tip! I was ready to give up on it |
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