Hi everyone.  I recently finished up my turbo budget effort of putting together an AR-RPK, and rattle canning it, and I'd like to see some other ideas or get some thoughts on the concept.

I figure an AR-RPK is the most practical LARP, SHTF, Doomer, Zero Hedge aficionado type rifle.  Its supposed to shoot a higher volume of rounds, its meant to shoot of a bipod, its got some magnification, mine does anyway, its not meant for door kicking or slicing the pie.  It sounds great for being in one place and holding what you got.

My build:

- Poverty Pony lower
- Del-Ton mid-length medium profile 16" upper, with a melonite gas tube, this upper has shot really well for me considering the $300 I paid for it
- YHM 0.5" riser rail
- PA 5x prism on a LaRue mount, traded a guy 12 ounce of silver for it, then put it on a KRAM spacer
- Rear folding iron is that company from the Holy Land, I forget the name, surprisingly inexpensive
- 2x Pmags, the only linked magazines I own
- Surefire G2X with Lumens Factor tailcap, in a IWC mount
- Del-Ton LPK?  Maybe a NBS LPK from AR15 Discounts?  I did some "trigger work" and its very nice while still being reliable
- Magpul stuff, STR, K2 grip, handguard, bad lever, I actually started coming around to these a few years later for a couple different rifles
- Midwest Ind 9 slot pic rail on handguards, gets far enough back that I can put a QD vertical grip on there if I wanted to I guess
- Versa-Pod bipod, I like somethings about it and hate others.  IDK, I'm not the bipod expert, but I did want something QD and its was half off the normal price

The ammo bag:
- Just a dyed UPC 200 round saw pouch with a 2Q canteen strap spray painted green
- Carries 7 Pmags
- Ideally carried by whoever I can press into service with the promise of adventure








And since night is half the day:

- Bering Hogster R-35
- My assistant's AGM-256




I'm really interested in anyone else's builds or thoughts on the topic.  I'm pondering picking up a 20" chrome lined heavy barrel for a second one and dumbing this one down, lightening it up, some.

I've seen the Klein uppers.  Those are really nice, but a little on the gigantic side.

Nice build.  I was expecting a 20" HBAR barrel however.  Colt and Shrike industries have marketed box and belt feed M16 for this role in the past.  IE Automatic Rifleman concept.
Colt Automatic Rifle
Fightlite
ARES Shrike

CD

Thanks.  I think I just need to make that 20" heavy barrel happen here at some point.

What I've got is pretty decent, the medium contour barrel is better than halfway there when shooting, but what's one more rifle?

The Colt is what tickled me right on this in the first place.

Any recommendation on triggers?  I've seen people use binary triggers for the role, but I'm wondering if there's a traditional trigger that'd be well suited?

I did one of these as an experiment with the KAC IAR handguard - it's a really cool concept but lacking any sort of fully-automatic capability means that it's academic at best:

I'm really far from an expert, but, my thought process is "rapid sustained fire" rather than "full-auto fire".  I do get what you're saying though, it seems like a legit automatic rifle would have a far easier time of keeping a beat going.

Brent, in the video, seems to have an easy time working things with that binary trigger, I've no experience with them though.  I'm interested in people's thoughts on those, and think about it specifically for this application.  Is there a short reset trigger that would be better?

This is a turbo poverty build, but if I do another, it'll be with more effort/cash.

Thoughts on bipod placement?  I'd like to stay with plastic two piece handguards, my experience with free float handguards is a mag of rapid fire and they get too hot to handle without gloves in the Texas sun.  Is there a rock solid bayonet pic rail so I can get that bipod out just a little further?

Thoughts on D60's?  I loath the thought of carrying one around, but is it worth the money to have one in the rifle?

Yes, they are worth it to have a couple for in the rifle.  My several examples are reliable.  I wouldn't carry one as a spare if moving, but one in the rifle or stashed near a static position, they are nice.

Load carriage solutions for the D60 inevitably suck. I might keep one on the gun for the initial usage but then you need to find a spot to stash it when empty. The Surefire 60rds might work well in this capacity if they're reliable. Personally I think that some PMAG40s with +5 baseplates would be the best compromise as long as you're not worried about bottoming out in the prone.

In your case I would put the bipod on the handguard or on a rail attached to the FSB. Yes, it'll affect accuracy in the prone but the idea is suppression and not precise shots, right?

Check out green mountain barrels for a finned barrel. I've thought of building something similar. One of my carbines has a socom barrel a Daniel defense omega rail. I could throw my d60 and gg&g bipod on it and get most of the way there.

I think the D60 is absolutely the best way to go. If you don't want to carry spares then D40s for reloads are the way to go IMO.

D60’s are a must and a very grip too. You can carry d60’s in saw pouches and having a very grip makes life easier so you won’t have to touch a super hot rail.

Good job, cool concept.

I have discussed this with others at length, it is a worthwhile pursuit.

I would say go 18 or 20" barrel, fluted or finned for cooling, free float rail for same.

Good choice of optic for a support by fire position, either that or 3x might be better for wider FOV.

Bipod yes, D60 and 40 rounders yes, VFG yes for avoiding the hot rail when it's time to pick up and hit the LOA!

I built this upper a while back with the goal of an RPK type build. I used a Wolf A1 piston system and a proto/retro style upper receiver with a 17.7" BA barrel. Would have preferred a heavier and longer barrel, free float handguard, and non-folding front sight, but was limited to what was available at the time. I did swap out the lower handguard for a metal picatinny model, but still need to pick up a bipod.

Attached File

If sustained fire is the goal, why not go with a free float rail? No POI shift due to bipod loading, easier to add other crap, and better heat dissipation. Midwest Industries even makes drop-in rails so you don't have to remove the barrel nut to install.

That's what I was thinking at most with a D60.  Immediate thought is I could just dump pouch the D60 and reindex 40's.  But I really like the idea of carrying the bulk of the ammo for this rifle in 200 round SAW pouches, or some equivalent, this is in addition to someone's normal LBE.  I don't have a super crew, but I do have a few folks I've pulled together with during a couple of really bad weather events, and we've thought experimented this out.  Two guys each carrying a SAW pouch full of 7 mags, the "assistant" drops or just flops his pouch next whoever has the AR-RPK, opens it, and then can get a little space.  I'm probably going to grab some buckles and legit webbing for the SAW pouches, so I could easily doff it while prone.

I can get those seven 30 round Pmags in one 200 round saw pouch.  I might be able to get two D60 in there?  210 rounds vs 120.  All of my other LBE is setup for 30 round mags as well.  I'll have to pick up some 40 rounders and see how those play with the gun, I imagine they'd work alright from the prone.  I might put together a new belt for this rifle that could carry 40 rounders if it makes sense, kind of sounds like it does.

Minute of man is the order on this one.  I just need a recommendation on FSB rails for it.


Sounds like the hive has spoken on D60's.

I'll check those barrels out!



Its just the idea of carrying 3 D60 when 9 or 12 30 round mags could fit the same volume is what gets me.  Maybe there's a better way to haul D60's and I just haven't seen it.  Something to research.



I had the same thought about 5x vs 3x, but I already had the 5x.  I might look at a 3x for the next iteration.  I could always move this optic over to a new gun and I've got a PA 2.5x that could go onto this current one.

In fact, most of this gun is what I already had on hand, like the upper and furniture, with the intent to see what I liked and what could be better the next time around.  Just happening to have a medium profile barrel is most of what got me going.  It's most of the way to an HBAR, far less material after the FSB though.

A full time vertical grip is something I'll look into.  Let me know if you know of any HBAR 20" finned barrels I should look at.


Sounds like 40 rounders are universally endorsed.



That is an extremely cool and unique upper!  You know from all the RPK's I've looked at some have heavier barrels and some don't.  Maybe its not that necessary for some doctrines or the trade offs weren't worth it for them?

My personal experience is they get crazy hot during rapid fire in our weather.  Like so hot I had to grip exclusively onto the little nub Magpul vertical grip.

I'm not totally opposed to them, maybe my Troy Mlok just sucked.  I know having the the gas block under the rail doesn't help.  11" rail with carbine length gas.



The gas block sits about half way up the rail.

With the originally pictured upper, zero issues handling that and rapid fire.  I know the idea is supported shooting, but I'd still like to avoid handling a super hot rifle if I can help it.

The right way to do it.

I forget who had the BumpSAW with M249 handguard.

Base line established here, I guess the purpose of this thread is to figure out "what's the best way to do it wrong?"

So far we've got:

- 20" HBAR
- Bipod
- 40+ round Pmags
- 3-5x magnification
- Mystery trigger, not yet identified
- Most likely a free float handguard, though I'm a slightly dubious on its necessity
- Forward vertical grip

In the military context think besides RPK also the M1918 BAR and vz26/BREN.  A light automatic rifle, providing a base for fire for the squad to advance/flank.

Advantages of a bipod forward is stability.  Cons lack of mobility in traversing.
Advantages of bipod in front of receiver are its ability to traverse side to side, Disadvantage is less stable.  
The MG42/MG3 allows the bipod to be attached under rear sight or forward just behind front sight.  Giving you both options.  On an AR15 with a forearm that has pic rails/M-Loc then you can also position the bipod in any position as the situation dictates.  
RPK, MG3 and M1919A6 (missing buttstock) with bipod mounted forward.
Attached File

MG3 mounted in rear bipod position on pedestal.
Attached File

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BREN Mk II bipod mounted about 1/2 way.
Attached File


Other note on buttstocks, when an LMG is used off bipod, support hand is usually repositioned to rear of buttstock for support.

Barrels are usually long for maximum velocity.  Heavy barrels are used as a heat sink to absorb heat from automatic fire.  Fins/ribs are to help providing more surface area to dissipate that same heat.  Larger box mags or drums for longer sustained fire/interval.  40rd mag/75rd drum on RPK.  Red Dots such as the Aimpoint M68 were ideal on a M249 in urban environments.

Great notes to add.  Excellent photo reference.  I never noticed how well thought out the MG42's stock was.

So far we've got - V2:

- 20" HBAR
- Bipod
- 40+ round Pmags
- 3-5x magnification, don't discount RDS depending on use case
- Mystery trigger, not yet identified
- Most likely a free float handguard, though I'm slightly dubious on its necessity
- Forward vertical grip
- Variable bipod mount location
- Clubfoot stock, or prone position optimized stock

Trigger is Diemco open bolt trigger group. This is a real LSW machine gun. Handguard is not free floated.

I just put one together using a Windham 16" dissipator-style heavy barrel on an SP1 upper receiver.

/\ This is the way.

But:  1.  I do like the idea of a 2-position bipod.(forward and mid mount)
       2.  I can't justify the use of a drum for other than range/fun use. (bulk/weight/capacity/cost vs 6-7 30-rd mags)

This is something I'm working on.  Still have barrel work to do.

Could it have been @jaqufrost?  Or, maybe @AlaskaCajun and @CccpNyc.

Not sure whose this is.  There are a few out there.  (from several ARFcon bumpsaw threads)

Do you have the details on that good buddy?  Looks like the barrel is still waiting on some FSB attention?

Sure.

The important stuff:

1. A1 butt stock, extended and handhold added.
2. 80% lower receiver with BK Firearms LPK (Binary to come later)
3.Anderson no-forward assist upper
4. E2 Armory M16 BCG
5. Franklin Armory 20" VS4 1:8 Bull Barrel (discontinued)
6. DPMS .936 FSB
7. Cavalry Mfg. C5 "fat" Hand Guards
8. M249 bipod

Yes, the barrel needs a lot of attention (mount FSB, thread muzzle for Flash Hider).  I'm thinking of making a bracket that clamps to the barrel under the sight base for mounting the bipod.  That way I could still mount a bayonet.  Also thinking about a vertical grip that goes through the lower hand guard and attaches to the barrel.

I considered using MI's clamp on 12" quad rail, but this thing is heavy enough already, and rails tend to get things attached to them!

I want that

That's a really nice build!  Definitely, gives me somethings to think about.

A bull barrel that need gunsmithing is probably outside my commitment level for this, but I can see yours ending up being outstanding.  I think great minds think alike and I'm going to stick with drop in handguards for my next one.

After seeing that bump saw deal, I'm going back and forth on a HBAR 16" mid length or a 20"...I don't have a lot of opportunities to shoot past 300 yards, but there's the barrel mass for heat consideration.

My rails also end up getting a light, maybe a grip, and then just $40 worth of rail covers.

Thanks for the photos!

Your point about the gas block being underneath the handguard is important, especially with a rail that fits closer to the barrel. I would think a wider rail with the gas block immediately past the end of that rail would be a good option. VFG if heat is really a problem after that.

QCB helps as well as top mounted magazine.

I'd like to get a different bipod setup, but this is how mine sits now.

Attached File

Not my thing, but fuck yeah.

Go for it.

Haha my minuscule ammo fort cannot handle feeding support weapons.

I dig it.

ETA:  I'm a totally savage, so I'd try out a the best barrel clamp pic mount, and I'm sure the "best" out there is still some $20 china special, and run a bipod of that.




I'm going to have to bank away some ammo for this rifle specifically.


Once I get this other rifle sold, I'm going to put this one together.

Good luck on the build OP.  I have this one.

Here are some photos of a configuration that Daniel Defense did for Argentina, 18 inch barrel.

Yours is outstanding, thanks for sharing that!

What kind of bipod setup is that?  I'm still on the QD bipod wagon, and I've got an idea for getting it further out on the gun.  Ya'll either call me a clown or a genius when I put it together.

I think I'm going to stick with a collapsible stock...I've got ideas of running a support hand grip on my 3d printer.  Something that'll interface with the sling loop on a Magpul STR.

The fixed stock on yours is makes for a very clean looking rifle.

I agree with him on the quad mags and the receiver not worth the hassle for a historically troublesome magazine design. The quad mag keeps popping up in gun design and gets abandoned every time. There receiver and mag are a neat idea though and hopefully they make money on them.

What's the heaviest 20" barrel on the market now that's not precision oriented or nitride instead of chromed? Anyone have any ideas? With a FSB would be great.

I'm thinking about 3d printing a LSW handguard.

Only thing I'm really seeing is the Del Ton.

The Diemco LSW is the heaviest barrel and needs a special bored out front sight to fit it. The barrel is .975" in diameter.


I sell LSW repro handguards if you need them.

I don't think they're commercially available are they?

I'll hit you up about those handguards.

Alright, I got most of my build ordered.

I ended up going with a Del-Ton 20" chrome lined HBAR upper.  I'm going to rock 2 piece handguards for now, Magpul ones, and I'll see how that handles.

I'll update with pictures once she's done, but ya'll keep posting so it don't get archived.

I'm still in for trigger recommendations.  I'm don't want to drop hundreds on triggers when I know plenty of ya'll are going to have great thoughts on short reset triggers that I should look at.  I'm off the binary trigger wagon.  I watched way too many video reviews of people saying, "these are great!" as they cleared a FTF hammer follow for the fifth time.

This thread makes me want a HBAR 20” and a few more d60s

Two things:
What’s the idea on a handguard? 13-15” free float? Something strong like a Larue?

What optic? Maybe a 3x primary Arms prism?

What’s the details on the carry handle?
@dex223

@03rn
No 20” finned barrel? Seems like just a 16”…?

Yeah and they're out of stock and nitride

Been following this thread with interest and also watching vids on the Red Right Hand LMG upper builds. They're using an aluminum heat sink that surrounds the barrel and a finned , straight gas tube. What do you guys think about this vs. just a heavy barrel and something like an inconel gas tube? Just thinking about how a real RPK doesn't really deviate that much from an AK, maybe keeping an AR-RPK closer in build to an AR is a better approach instead of extra proprietary stuff.  

https://redrighthandllc.com/product/lmg/

One of the binaries uses a sear trip lever to avoid hammer follow. Fostech Echo, I think. I don’t know what the legal status, or future legal status is.

I was thinking about the huge diameter Aero one and a picatinny folding carry handle.

One of the binaries uses a sear trip lever to avoid hammer follow. Fostech Echo, I think. I don’t know what the legal status, or future legal status is.

I was thinking about the huge diameter Aero one and a picatinny folding carry handle.

If you're looking for some additional barrel cooling, check out https://jprifles.com/1.4.5_hs.php

^excellent, thanks for sharing this!