this post was submitted on 21 Jan 2026
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First time building something from scratch (lemmy.world)
submitted 3 months ago by frog_brawler@lemmy.world to c/guns@lemmy.world
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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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[–] Beacon@fedia.io 13 points 3 months ago (1 children)

Non-gun person here. What does it mean to "build a gun from scratch"? Like surely you aren't manufacturing any of the components yourself, right?

[–] frog_brawler@lemmy.world 19 points 3 months ago (1 children)

Same concept as building a gaming computer. Pick out each individual part, then assemble (like Lego)

[–] Beacon@fedia.io 8 points 3 months ago (2 children)

Huh, TIL. And i assume many but not all components are inter-connectable with each other. Thanks

[–] frog_brawler@lemmy.world 8 points 3 months ago

Yup, AR-15 platform parts are widely available / widely compatible.

[–] setsneedtofeed@lemmy.world 5 points 3 months ago

ARs are specifically known for their LEGO like modularity. Even a person without bespoke firearms tools and just Youtube advice can do things like change the trigger and the controls out. It only takes a minimum of specific tools (mainly an AR-15 wrench) to change out the buffer tube. Many other parts of this like the optics and handguard accessories setup are just bolt in or clip in.

[–] papalonian@lemmy.world 6 points 3 months ago (2 children)

Solid color coordination. Looks good.

I'm happy to be wrong, but I'm pretty sure your magnifier is meant to be mounted after the optic, so that the dot / cross hair / whatever you've got doesn't get magnified, and so that you're not so far away from the optic when your magnifier is flipped over.

[–] frog_brawler@lemmy.world 3 points 3 months ago* (last edited 3 months ago) (2 children)

Thanks for the feedback, and I appreciate the response.

This setup requires the magnifier to be closest to the eye, otherwise you won't be seeing anything through it. If I extend my stock on position 2, my eye is too far away. Stock stays at position 1 on the buffer tube.

One cool thing about this red dot is that it's actually a double dot, one in the middle, and one slightly below. You zero based on the middle dot, and expect the lower dot to be accurate at some other distance that I'm not fully looped in or aware of just yet.

I zero'ed to 50yards, but I haven't aimed at anything that's 100 yet. Maybe that's what the lower dot is supposed to be? Fingers crossed I'll figure that part out this weekend.

[–] Theatomictruth@lemmy.dbzer0.com 5 points 3 months ago* (last edited 3 months ago) (1 children)

When zeroed at 50 yds the lower dot is supposed to be 500

At 100 yards I believe you should expect to be hitting slightly above the center dot

[–] frog_brawler@lemmy.world 2 points 3 months ago

Right on, thanks!

[–] papalonian@lemmy.world 1 points 3 months ago (2 children)

This setup requires the magnifier to be closest to the eye, otherwise you won't be seeing anything through it.

Hm. If it works it works, I won't try and say that you're doing it wrong, but pictures of the combo you have on the company's website primarily shows the magnifier after the optic, which is how these are typically mounted. You'd think it would at least be possible.

I know when setting mine up it took a lot of finagling to get the two perfectly in-line with each other. That could be why it only works in the one way. But again, I supposed if it works, no harm no foul.

[–] setsneedtofeed@lemmy.world 1 points 3 months ago (1 children)

which is how these are typically mounted.

By whom?

[–] papalonian@lemmy.world 1 points 3 months ago (1 children)

It took way longer to find those pictures to prove your point than it would've for you to scroll down 2 or 3 comments to see that I already said I was wrong, hours ago. Thanks, though

[–] setsneedtofeed@lemmy.world 1 points 3 months ago (1 children)

I'm genuinely asking, since you have apparently a magnifier that does mount like this.

[–] papalonian@lemmy.world 1 points 3 months ago (1 children)

My setup is very similar to this, but with the magnifier much closer to the optic. The one I rented at the range was the same way.

[–] setsneedtofeed@lemmy.world 2 points 3 months ago

Monstrum makes sense. They sell a lot of prism optics, which by their nature have defined eyeboxes. They do have a magnifier with a long eye box on their storefront. This is a very uncommon setup.

Red dots or holographic sights don't have limited eyeboxes, which is why is every setup with them and magnifiers the magnifiers are in the back.

[–] frog_brawler@lemmy.world 1 points 3 months ago (1 children)

Ehh… which picture? It wasn’t the one on EOTECH’s site.

I can assure you, if the red dot went before the magnifier you wouldn’t be able to use the magnifier at all. Eye relief.

Additionally, you cannot distinguish the second red dot without the magnifier.

[–] papalonian@lemmy.world 3 points 3 months ago* (last edited 3 months ago) (1 children)

Ehh… which picture? It wasn’t the one on EOTECH’s site.

https://www.eotechinc.com/products/eotech-holographic-hybrid-sight-vi

The photo gallery of the product page only shows it with the magnifier after the optic (the optic listed is the EXPS3-2, but they seem to largely be the same product).

Edit: ignore literally everything I wrote. Lmao. The optic is facing the opposite direction I thought it was.

[–] frog_brawler@lemmy.world 4 points 3 months ago

The optic is facing the opposite direction I thought it was.

😀 All good

[–] Romkslrqusz@lemmy.zip 2 points 3 months ago (1 children)

pretty sure your magnifier is meant to be mounted after the optic

Every magnifier I’ve ever interacted with went before the optic. They usually have short eye relief, putting one that far forward would make it unusable.

[–] papalonian@lemmy.world 1 points 3 months ago (2 children)

OP has corrected me on this setup (and I embarrassed myself by linking supporting material to their claim), but the two that I've used (one is my own) has the magnifier second. I think it really just depends on the magnifier. My magnifier is long enough that, if you were to flip it to the side and rest your cheek before it, the optic would be way too far to be able to use

[–] setsneedtofeed@lemmy.world 2 points 3 months ago* (last edited 3 months ago) (1 children)

My magnifier is long enough that, if you were to flip it to the side and rest your cheek before it, the optic would be way too far to be able to use

I'm now genuinely curious what magnifier you have. I've never seen a sideflip long eye relief one.

I have a friend who put his magnifier on his handguard and didn't realize anything was wrong with looking through the magnified pinhole until I corrected him.

edit:

the optic would be way too far [away] to be able to use

What are you magnifying?

[–] frog_brawler@lemmy.world 1 points 3 months ago (1 children)

Concur, but I also recognize that I haven’t used everything. I’d be impressed if we’re both incorrect but I suspect we’re not.

[–] setsneedtofeed@lemmy.world 1 points 3 months ago (1 children)

After some questioning I found they were talking about a magnifier setup made by Monstrum for their prism optics. Since the prism optic has an eye box, the magnifier can be set up and adjust for long eye relief.

This is a pretty wacky setup by a company that makes cheap optics but it does exist. Really a different beast than magnifying a holographic optic.

[–] frog_brawler@lemmy.world 2 points 3 months ago

I really want to look through this setup now.

[–] frog_brawler@lemmy.world 1 points 3 months ago

I think you might benefit from switching positioning, re-zeroing, and checking out how much better things will work if your magnifier is closest to your eye.

I’ve got 3 different mag/dot combos. They all need the magnifier closer to the eye vs the dot.

I may be wrong, but I’ve not personally encountered an example that makes me incorrect.

[–] jordanlund@lemmy.world 5 points 3 months ago* (last edited 3 months ago) (4 children)

I'm not PERSONALLY a fan of FDE, but the contrast looks good and the build looks solid!

I'm a wood and brass kind of guy. 😉

.45-70 Government

.44 Magnum

[–] Whostosay@sh.itjust.works 3 points 3 months ago (1 children)

First ones a beaut, what's the scope on that

[–] jordanlund@lemmy.world 2 points 3 months ago (1 children)
[–] Whostosay@sh.itjust.works 2 points 3 months ago (1 children)

Neat, looks really good on that rifle

[–] jordanlund@lemmy.world 1 points 3 months ago

I specifically wanted a brass scope and it was either that or something that wasn't really functional. 😞

[–] frog_brawler@lemmy.world 2 points 3 months ago (1 children)

The .44 Magnum looks like it has a lot of kick. Both look great!

[–] jordanlund@lemmy.world 2 points 3 months ago

I mean, .44 mag is .44 mag, but it also weighs almost 6 pounds.

[–] JoMiran@lemmy.ml 2 points 3 months ago

Nice 45-70. I think my next buy will be a Marlin Trapper 1895 if I can find it. If not, SBL 1895.

[–] rabidhamster@lemmy.dbzer0.com 2 points 3 months ago (1 children)

Wood, you say?

[–] jordanlund@lemmy.world 2 points 3 months ago

Who doesn't enjoy wood furniture? 😉

[–] sic_semper_tyrannis@lemmy.today 2 points 3 months ago

It's so fun to build your own! I did too

[–] setsneedtofeed@lemmy.world 1 points 3 months 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 3 months 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 3 months 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 3 months ago* (last edited 3 months 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