this post was submitted on 21 Jan 2026
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LMT Mars-L Lower, LMT 9.25" MRP upper, LMT 10.5" 300BLK Barrel, Geissele SSA-E (3.5lb), magpul furniture, EOTECH G43/EXPS3, Vltor A5 buffer, Radian Raptor Charging Handle, Bootleg adjustable BCG, Sandman-X can., POS Hexmag (need to swap this out)

This is my first post to this community. I didn't realize the community was here... but generally speaking, Lemmy needs more posts, so I'm putting this here in an attempt to do my part.

Last year, I was thinking about upgrading my Ruger 8515 to something a bit higher end and ultimately decided it would be better to build one from the ground up... did a lot of research, saved a lot of money, waited a lot of months and came out with this thing. Got the Form 1 stamp back yesterday.

It's pretty nice, but it's a slight bit heavy for an SBR @ 10lbs (loaded and with the can). I like it though. It's more difficult to shoot than the 8515, but I've only taken it out once so far (last night), so I still have some "getting used to it." There's also a light and an extension for said light on the way here now, so by this weekend I think it'll be "done done."

It's completely solid w/o the can using 150gr Federal. Once I put the can on it and switched to subsonic ammo (Hornady Black 208gr), I had failure to feed after the first round. My assumption is that my buffer weight is too heavy (currently on A5H2 that came with the Vltor kit) so I have an A5H0 on the way here now. Fingers crossed I'm right. It's whisper quiet, and if I can get it consistent, I'll be in love with this thing.

I only have a handful of friends that are into this hobby, and I don't want to send them pictures or let them know it's done. I'd rather whip it out as a surprise at the next range day.

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[–] setsneedtofeed@lemmy.world 1 points 14 hours ago (1 children)

With the BCG as the adjustment method for putting a can on, what do you think? I'm used to adjustable gasblocks, though I suppose for your handguard setup the BCG is more accessible.

[–] frog_brawler@lemmy.world 1 points 14 hours ago (1 children)

I need to get back to you on this, probably late Sunday/ sometime Monday. I just got the A5H0 buffer yesterday, and won't have an opportunity to test until Sunday.

My initial thoughts from the first time I took it out were that the adjustable BCG wasn't doing shit, and a mid level of disappointment.

I went with the adjustable BCG because this is the MRP and the gasblock is attached to each barrel and cannot be adjusted. That's part of why I went with the handguard setup I have, since it's not going to impact it either way and it feels great. I want to be able to swap out my barrel for 5.56 (next time there's a sale at LMT). Going to go 14.5" on the 5.56 but priority is 300 BLK @ 10.5". I'll keep the A5H2 and A5H0 in the case and just switch out the buffer weight if I change caliber.

Plan is legit dual caliber and my case has a spot for the torque wrench and barrel swap. My first rifle was a Ruger 8515 and I have a ton of mags for that already. That's also why this build I went with FDE. I want my FDE to = 300BLK, and black mag = 5.56. Black electrical tape on the subsonic rounds of 300blk, and green painters tape on my armor piercing 5.56.

[–] setsneedtofeed@lemmy.world 1 points 13 hours ago (1 children)

What (if anything) is the goal of the setup in terms of driving choices like barrel, optics, handguard, accessories?

[–] frog_brawler@lemmy.world 1 points 13 hours ago* (last edited 12 hours ago)

end goal is home defense and flexibility - the whole LMT MRP setup will allow for me to swap out to 5.56 and use all of this other ammo that I already own.

Optics - astigmatism primarily drove that choice, but also some preexisting familiarity.

Handgrip choice came from stock preference... I like the B5 E-SOPMOD on my 16.1" but I can't put that on an A5 buffer system and have it actually retract all the way. It ends up sticking out like 1/4-1/2" and I hate that. I'm a nerd and I want things to fit perfectly. I went with the A5 buffer to reduce recoil. That being the case, I didn't have a lot of options with the A5 buffer and the Magpul STR was one of the two options that I could find that actually fully retracted on the A5 buffer. Once the stock was figured out, I wanted the rest of the furniture to match.

The light is a M640V which works really well with the EXPS3