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Posted: 5/18/2024 2:38:17 PM EST
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. |
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Posted: 5/18/2024 3:10:04 PM EST
[#1]
My son is talking about getting one of those kits to add to his piles of rusty metal.
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Posted: 5/18/2024 4:03:38 PM EST
[#2]
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.
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Posted: 5/18/2024 7:26:46 PM EST
[#3]
I had about 10 MG42 kits, with cut receivers and extra barrels.
Wound up selling them all.  |
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Posted: 5/23/2024 5:41:46 AM EST
[#4]
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.
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Posted: 5/23/2024 6:32:48 AM EST
[#5]
Quote HistoryOriginally Posted By cms81586: 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. |
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Posted: 5/23/2024 9:35:56 AM EST
[#6]
Quote HistoryOriginally Posted By BASE: 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). |
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Posted: 5/23/2024 10:02:35 AM EST
[Last Edit: BASE]
[#7]
Quote HistoryOriginally Posted By cms81586: 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. |
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Posted: 5/23/2024 10:51:21 AM EST
[#8]
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.
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Posted: 5/23/2024 11:16:24 AM EST
[#9]
I don't think there is anything to set, or pin with these.
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MP, USA
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Posted: 5/23/2024 1:57:19 PM EST
[Last Edit: JoshNC]
[#10]
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. |
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Posted: 5/23/2024 2:54:44 PM EST
[#11]
Quote HistoryOriginally Posted By cms81586: 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. 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. |
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MP, USA
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Posted: 5/23/2024 3:17:57 PM EST
[#12]
Quote HistoryOriginally Posted By BASE: 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. |
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Posted: 5/23/2024 3:24:36 PM EST
[#13]
Quote HistoryOriginally Posted By JoshNC: 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. Quote HistoryOriginally Posted By JoshNC: Originally Posted By BASE: 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. |
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Posted: 5/23/2024 3:43:21 PM EST
[#14]
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)?
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Posted: 5/23/2024 4:18:06 PM EST
[#15]
Quote HistoryOriginally Posted By JoshNC: 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. 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. |
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Posted: 5/23/2024 4:39:24 PM EST
[#16]
Quote HistoryOriginally Posted By cms81586: 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. |
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MP, USA
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Posted: 5/23/2024 5:51:33 PM EST
[#17]
Quote HistoryOriginally Posted By BASE: 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. checking bolt gap is easy. Then adjust with + or - size rollers. |
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Posted: 5/23/2024 9:04:17 PM EST
[#18]
Quote HistoryOriginally Posted By BASE: 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. Locating the feed box and getting the shroud straight due to warpage are going to be a bitch. |
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Posted: 5/23/2024 9:12:57 PM EST
[Last Edit: Jkees]
[#19]
Quote HistoryOriginally Posted By cms81586: 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. |
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Posted: 5/23/2024 9:16:27 PM EST
[#20]
Quote HistoryOriginally Posted By Jkees: 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. |
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Posted: 5/24/2024 1:50:44 PM EST
[#21]
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. |
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Posted: 5/24/2024 7:22:12 PM EST
[#22]
Quote HistoryOriginally Posted By BASE: 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. |
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PA, USA
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Posted: 5/25/2024 4:46:32 PM EST
[#23]
I ordered a kit too. Rcm said they are going to offer barrels for these kits.
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Posted: 5/25/2024 5:28:31 PM EST
[Last Edit: BASE]
[#24]
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… |
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Posted: 5/25/2024 6:05:58 PM EST
[#25]
Quote HistoryOriginally Posted By BASE: 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+… |
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Posted: 5/25/2024 7:19:09 PM EST
[#26]
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. |
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Posted: 5/25/2024 7:57:35 PM EST
[#27]
@RebleYell
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VA, USA
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Posted: 5/31/2024 3:12:50 PM EST
[#28]
Quote HistoryOriginally Posted By BASE: 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… I've heard the RCM barrel going for around 625 |
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Posted: 5/31/2024 5:21:50 PM EST
[#29]
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GA, USA
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Posted: 6/2/2024 2:35:21 PM EST
[#30]
My first set looked really decent .. second set looked like crap.. I sent an email to APEX .. the stock and lower look terrible. The bolt carrier and bolt have some minor surface rust, but they’re HK.
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Posted: 6/2/2024 4:11:08 PM EST
[#31]
I talked my son into buying one, and they're out of stock.
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Posted: 6/2/2024 4:12:45 PM EST
[Last Edit: Type7SOT]
[#32]
Quote HistoryOriginally Posted By Cpt_Kirks: I talked my son into buying one, and they're out of stock. @Cpt_Kirks https://store.centuryarms.com/fmp-hk21-parts-kit.html |
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Posted: 6/2/2024 5:54:17 PM EST
[#33]
Quote HistoryQuote HistoryOriginally Posted By Type7SOT: Originally Posted By Cpt_Kirks: I talked my son into buying one, and they're out of stock. @Cpt_Kirks https://store.centuryarms.com/fmp-hk21-parts-kit.html Thanks, I just pointed him at that. |
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GA, USA
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Posted: 6/5/2024 1:30:33 PM EST
[Last Edit: FNGfromGA]
[#34]
I ordered 2 kits from APEX.. One was not bad except for the Bolt Head the second kit was dookie as the lower was really corroded, the and the stock was really rusted. They were nice and said I could return it on my dime. I am rolling the dice and trying to order another one from Century, just to have some spare parts. I already have 2 Barrels from a Michaels Machine MM-11 , that I should be able to use. I am having one built out. I know that I will have to get some parts replaced by RCM.. (Probably Bolt, Extra Barrels, etc.) . I ordered some belts from RTG, as those that are smarter than I stated they are the best and links require mods on a 21.
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Posted: 6/5/2024 2:07:02 PM EST
[Last Edit: cms81586]
[#35]
I’ve started the demil process on mine. Thread is in the HK section. APEX was good about replacing some bad parts on mine.
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GA, USA
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Posted: 6/5/2024 5:03:18 PM EST
[#36]
FYI… I contacted Mike @ RCM, and with all of the kits coming in, he stated
“Hi we are making barrels, hybrid bolt heads, trunnions, rollers, locking pieces, t-rails. I will add you to the contact list. Please let the others know if you can. I'm not on the forum. Thanks” My understanding is that these are the common missing or worn components.. If you are considering a build, and need parts, email them to get on the contact list. [email protected] |
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Posted: 6/5/2024 10:54:05 PM EST
[#37]
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Posted: 6/6/2024 7:18:07 PM EST
[#38]
I still can't decide between a 51B or a 21 so I have another kit on the way. Hopefully I'll luck out a second time and not have to exchange any parts.
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Posted: 6/6/2024 8:03:11 PM EST
[#39]
Quote HistoryOriginally Posted By BASE: I still can't decide between a 51B or a 21 so I have another kit on the way. Hopefully I'll luck out a second time and not have to exchange any parts. I’d love a second kit to do a 51B but it’s not in the cards right now. |
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Posted: 6/8/2024 5:17:14 PM EST
[#40]
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Posted: 6/8/2024 5:36:07 PM EST
[#41]
Quote HistoryOriginally Posted By Cpt_Kirks: My son's kit: https://www.ar15.com/media/mediaFiles/61458/20240608_161620_jpg-3236029.JPG He building it himself? |
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Posted: 6/10/2024 12:36:27 PM EST
[#42]
Quote HistoryOriginally Posted By cms81586: He building it himself? Quote HistoryOriginally Posted By cms81586: Originally Posted By Cpt_Kirks: My son's kit: https://www.ar15.com/media/mediaFiles/61458/20240608_161620_jpg-3236029.JPG He building it himself? Oh yeah. He has a backlog of piles of rusty metal he's working on. |
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Posted: 6/10/2024 7:40:47 PM EST
[#43]
I was just getting into the MG-42 build and then these things came up.
A beltfed 7.62 that I can put a sear in pretty well makes everything else look lame so the other stuff is going right back into the "pile". |
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Posted: 6/30/2024 11:43:19 AM EST
[#44]
Getting off to a slow start on this one but I do now have a couple of receivers bent up. I've got a couple more mandrels and jigs to make before I start welding. My flats weren't in great shape IMO, but it's been a long time since I bent any receivers and I probably just didn't notice last time.
My new bending jig:    It ended up being kind of a 3 step process. Bending, then squeezing, then squaring the rails, then squeezing some more, then squaring again... Maybe it was more than 3 steps. The RTG G3 flat had crooked rails and the cetme one had really shallow rails. The last pic is me trying to deal with those issues. The worst one after giving it the above treatment:  That was the cetme flat. The G3 has really crooked rails at the front but wasn't hard to get them back into shape at all. The cetme took some force and never did square up quite as good. I think it's pretty good now but I'm a little out of my element here. I will work them over again after welding them up. If anyone is about to try this I'd reccomend making a something like a straightening mandrel and also having the reinforcement rails in hand. I found cheap A3 rails at RTG last week and bought some. They came in really handy for squaring up the rails. I believe they can be made to work as reinforcement rails as well if you want a more factory look with your build. |
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Posted: 6/30/2024 12:43:31 PM EST
[Last Edit: Pro_Patria_431]
[#45]
 Got some material for a straightening mandrel. |
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Posted: 6/30/2024 1:30:55 PM EST
[#46]
I didn’t put the top part on mine and kinda wish I had now. I should probably make a handle as well.
I’ve got a few other alignment mandrels and heat sinks I’ll probably make out of aluminum before I start welding it. I’m thinking of one that’s a shorter version of the straightening mandrel but with the bottom shaved up to where it will just clear the feed mechanism. Not sure that’s necessary but a big heat sink in there probably wouldn’t hurt. |
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Posted: 7/10/2024 4:04:31 AM EST
[Last Edit: barbcue]
[#47]
If there where ever 2 threads that needed to be *ONE*
It's this one and the "if you bought a 21 kit" thread in the HK forum. 2500 of these kits were imported that's not "a little" but its also "not alot" IMO - We need to bring this pair of threads under one roof, and also allow parts Buys and SWAPS in that thread ? (As rare as this varient is (1960's) there are still parts floating around some new and used and some hard to get for this particular model) we need a CUT LOOSE--- buy, sell, trade, gunsmithing, acquisition of parts (LINKS), and a casual rating of *customer service* from the various VENDORS that are selling these, etc etc. These kits are expensive and exotic and IMO deserve there own SUPER THREAD in the "HK FORUM" where it belongs. I'd start it or MOD it or SHUT UP- whatever is needed.  Mods if you have any ideas LMK.. Barby |
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Posted: 7/10/2024 4:04:42 AM EST
[Last Edit: barbcue]
[#48]
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Posted: 7/10/2024 8:05:45 AM EST
[#49]
The other author was probably a bit smarter in placing his thread in the HK subforum. His thread has taken off so that's probably the better resource. I've been following a few threads here, at HKPro and WG but it seems more are popping up weekly.
I really haven't made much progress yet. I've still got a few more tooling type items to make before I start welding. I also haven't had my TIG hooked up in about 15 years so I've been trying to knock the dust off there as well. I thought I used to be a pretty decent TIG welder but either my skills have declined, or I was never as good as I thought I was
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Posted: 7/10/2024 11:00:36 AM EST
[#50]
OP, I'm following both threads
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