I can’t remember the last time I saw 21 parts kits available but it looks like Apex has a batch.

https://www.apexgunparts.com/machine-guns/hk21-belt-fed-parts-kit-7-62-nato-308-good-a.html

Anyone else fighting the urge to give it a go?

I’m thinking of picking one up to use for an 51B build, if not an actual 21.

My son is talking about getting one of those kits to add to his piles of rusty metal.

I'm a bit of a rusty pile collector myself. I recently found a 25 yr old MG42 kit I had kinda forgotten about and I've been reading up on welding those things together. I don't need another project like that but it seems like a really good price. Even those old non-E feed mechanism parts are pretty pricey IIRC.

I had about 10 MG42 kits, with cut receivers and extra barrels.

Wound up selling them all.

I bought one. Century arms has them in stock right now for the same price too. bowman’s is proud of theirs and are asking $5100 for them. I have some reading to do and plan on buying a FMP barrel and tig welder before I start getting ready to put mine together.

I saw that on WG yesterday and almost bought another. I don't even have the kit yet and I'm agonizing over whether to build a 51B or just build it like it's meant to be.

I thought I knew how to put an HK together but I'm still figuring out how this one is going to go together. Not a lot out there on grafting in that feed box. I did read the other day that a new batch of barrels is in the works, I think it was BPP. Also looks like MM sells the e-versions anyway, for just over 1k.

From what I’ve read, most MM21 barrels aren’t a direct fit in an HK (or HK contract) trunnion without modification. I’m looking for an FMP barrel but I also will consider a BPP barrel…although those are HK21E spec (unless they do a run specific to these since so many kits came in).

Is there something beyond the 21 vs 21E pin that causes issues? I saw those barrels for 1k and almost bought one before realizing they were e-model barrels. I think they can be modded if there isn't something else going on but I'm not paying for a new barrel and then going through that trouble.

If the damn things didn't have the flutes in the chamber I'd attempt making my own.

I’m still trying to confirm how to set the bolt gap with these. I assume it’s a PITA trial and error process of setting the trunnion, inserting the barrel, checking bolt gap, rinse and repeat over and over until it s correct and then pin.

I don't think there is anything to set, or pin with these.

21E bolts have a different extractor that sits proud in front of the bolt and requires an extractor relief cut in the 21E barrel’s breech face. The 21E barrel also has the barrel safety pin that protrudes radially from the bottom of the barrel latch support. That pin engages the barrel safety latch in the shroud, which prevents the cocking handle support from going forward if the barrel isn’t fully locked into the trunion. This is also present on the 11A1 kits that were imported.

21 bolts use a standard G3 extractor. 21 barrels have a pin that ptotrudes from the breech face rearward. 21 bolts have a recess milled in the face that accepts the barrel pin. This is the barrel lock safety feature on the 21.

MM barrels use E extractor/bolt but use the 21 barrel pin for the barrel lock safety feature. They lack the E barrel safety pin and the shroud lacks the barrel safety latch.

BPP barrels are full E spec.

Either can be used in a 21 in a pinch. A 21 barrel cannot be used in a 21E without milling the extractor recess and removing the 21 barrel safety pin.

Bolt gap is set in a 21 just like in any other HK roller delay firearm by using the correct locking piece and rollers. It’s not hard. I’d  bet the bolt heads and locking pieces are at the end of their service life in these 21 kits. The 11a1 kits have bolt heads and locking pieces that are at the end of their service life. They can be rehabbed using a new locking piece then going up in roller size until the correct bolt gap is achieved.

Are you maybe thinking of headspace vs bolt gap? That sounds more or less like the process to set headspace in an HK with a pressed in barrel.

There is no setting headspace in HK roller delay firearms, whether the barrel is pressed and pinned or has a QC barrel. Bolt gap is what you set in all HK pattern roller delays.

Okay, I'm at a loss then. I think I've pressed them out and back in on both AK's and HK's... but I was a bad person and never bothered to check headspace on any of them.

While we are on the subject of bolt gap: Do you guys know if that can have any appreciable effect on the cyclic rate (or lack thereof)?

I guess what I’m getting at is how do you locate the trunnion in the receiver before you weld it on the HK 21. Forgive me…never built a G3 or one of these but I get now that it’s not the same because you aren’t populating a barrel/trunnion combo.

I think you slide it back until it hits the rails. I was mistakenly thinking the barrel sat a bit subflush in the trunion but now that I've looked a bit closer, def not the case. So I probably don't know what I'm talking about.

I spent some time interrogating a SOT friend over the weekend, asking lots of these dumb questions. I'm still not sure about locating the feedbox. He sounded like he'd had a traumatic experience with some built 11's and that he didn't want anything to do with a 21. I hope that isn't a sign of bad times to come, this will be one of my most expensive builds by the time I get a pair of barrels and the rails and all the other details collected.

checking bolt gap is easy. Then adjust with + or - size rollers.

Locating the feed box and getting the shroud straight due to warpage are going to be a bitch.

I imagine it wouldn't be too hard to put together some sort of 3d printed jig to layout cuts and to align the box.

Question is who will be the first to do it lol.

I won’t be building mine right away. I’m gonna mess with practicing tig welding on some flats for quite a while before I make an attempt. And I’ll also need to find a the barrel, receiver reinforcements, rear sight weldment, and semi shelf.

I'm guessing you've seen the sticky thread on the WG forum (HK/cetme subforum) on welding 21 receivers? Amazingly the pictures still load but it mentions a secret jig that is not shown to locate the feed box.

I'm planning on building a jig to bend the receiver and have no issues machining whatever is needed. My build projects are usually 90% jig/tool building and 10% gun building and I'm guessing this will be no different. I have to admit I'm at a loss as to how to design a jig to hold that box. Maybe I'll get some inspiration once the parts are in hand.

Same here. I spoke with Mike at TSC. He doesn’t do beltfed’s anymore…but did state that he had a jig. I didn’t pry on specs because those seem to be “trade secrets”. My kit shipped today. Once I have it on hand I’ll mess with it. I’m not convinced a jig is necessary. Tack it and test it. If it needs moved then move it. Use the feed pawl pin that rides in the groove on the bottom of the carrier to dictate where the box needs to be. May take some trial and error but it’s not impossible. Lots of home built 21’s out there.

I ordered a kit too. Rcm said they are going to offer barrels for these kits.

Anyone hear an est on what the barrels from RCM are going to cost? Or when to expect them?

I emailed the other day and got a response that I was on the “contact list”. I think someone said ~500 but that seems almost too good to be true.

A while back I saw one for sale that was a 14-incher which I had never seen before but it got me thinking…

If they’re $500 I’m buying two. But they will be $1k+…

I was guessing 1k. Can’t remember who posted that now. I’d buy a bunch if they were that cheep.

That’s got to be a bitch to machine.

@RebleYell

I've heard the RCM barrel going for around 625

These things are in decent shape.

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