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If you bought an HK-21 kit get in here! (Now a build thread…) (Page 13 of 17)
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Originally Posted By Type7SOT: Need some help here. My gun is completely together but its having an issue advancing the belt. First of all, yes the lug on the belt feed mechanism is engaging with the bolt carrier. However, this part: https://www.ar15.com/media/mediaFiles/490765/1000008615_jpg-3426076.JPG I think you are correct that is a spring issue. Desert Yankee (one of the HK21 builders) has a video on YouTube where he mentions this problem a bit: Video The part you might need is available from Center-fire systems. There are two types: Type 1 And Type 2 CFS also seems a complete feed mech if you just want the whole thing. I have no idea how to change the part/spring out |
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Originally Posted By Mrf2: I think you are correct that is a spring issue. Desert Yankee (one of the HK21 builders) has a video on YouTube where he mentions this problem a bit: Video The part you might need is available from Center-fire systems. There are two types: Type 1 And Type 2 CFS also seems a complete feed mech if you just want the whole thing. I have no idea how to change the part/spring out Thank you, this pretty much confirms what I was thinking. I can remove the spring in question (I've done it twice already) but I'd rather replace it with a brand new spring. Maybe I'll try to find something on McMaster Carr. |
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Originally Posted By Type7SOT: Need some help here. My gun is completely together but its having an issue advancing the belt. First of all, yes the lug on the belt feed mechanism is engaging with the bolt carrier. However, this part: https://www.ar15.com/media/mediaFiles/490765/1000008615_jpg-3426076.JPG Seems to have an issue. It seems like it is supposed to be biased to the left, being driven by a spring inside this part: https://www.ar15.com/media/mediaFiles/490765/1000008616_jpg-3426077.JPG But it doesnt always snap all the way to the left. Frequently it will go about 80% of the way to the left then stop. When this happens you can pretty easily push it with your finger the rest of the way. There doesnt seem to be any binding, almost like the spring in picture number 2 isnt strong enough. Does anyone know where I can get a replacement spring? Or, is there something else wrong and I'm misdiagnosing the issue? Mine does that as well but functions perfectly in the gun and runs, when the bolt goes back and forth it should work that just fine even if your spring can't get it back on its own. Mine does exactly what you describe, but the feed mech runs fine. Try this. Use your finger to advance that lug to the right, does the sprocket spin? Keep cycling the lug back and forth, even when you got a help it "reset" and Make sure to go around all the way and make sure every time it spins the sprocket. The part linked below is known to cause advancing issues, hence why it sold out fast, someone prob bought them all. My feed mech, and also a buddies this was the exact part that was causing feed mech not to advance https://centerfiresystems.com/hk21-feed-mechanism-complete-feed-shaft-assembly/ |
 HK21 with "E" upgrades, FMP HK 21 Hot linked it for you. Very nice. Me so jealous and in need of a registered sear. |
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| Another observation, and let me know if anyone has similar or not experience. My RCM barrels all gap higher then my FMP barrels. Significant enough to where you may want to adjust rollers. So just make sure of you are gonna swap back of forth between FMP / US made, your check gap. |
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Originally Posted By Heineken: Started off a little cocky and had to reset my feet ...but then got my shit together and finished strong for you guys  https://youtu.be/s4FDQRd0jro?si=sJ0uJkS4wsQjTXAs Damn, this is my new favorite HK. I'm gonna get another one done. Heineken !!!! |
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Originally Posted By Heineken: Another observation, and let me know if anyone has similar or not experience. My RCM barrels all gap higher then my FMP barrels. Significant enough to where you may want to adjust rollers. So just make sure of you are gonna swap back of forth between FMP / US made, your check gap. That’s what I’ve found too. Jeff Walters posted about it on HKPro that RCM did this on purpose. IIRC, I found it to be about 0.05-0.1mm larger gap in three different HK 21A1/11A1 trunions with new 21E bolt group and -4 rollers. |
| Waiting to get some decent weather so I can sand blast this thing and then paint. Bought HK Black Duracoat and then Colt Grey for some of the smaller parts that were originally just parked. Otherwise it’s finally done. Anyone here who bought a kit and did it on their own get theirs done or close? |
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Originally Posted By cms81586: Waiting to get some decent weather so I can sand blast this thing and then paint. Bought HK Black Duracoat and then Colt Grey for some of the smaller parts that were originally just parked. Otherwise it’s finally done. Anyone here who bought a kit and did it on their own get theirs done or close? I was hoping you were going to go with the RAL color. I kinda just want to see one that color. |
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| Have a kit from Centerfire Systems but have been hesitant to start. Question for those who have built or at least completed welding - how do you ensure alignment of the various components such as shroud/trunnion, receiver, and feed mechanism housing to receiver? It seems that even slight misalignment or miss-location of components could cause feed or function problems later. Thanks in advance. |
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Originally Posted By ghall4: Have a kit from Centerfire Systems but have been hesitant to start. Question for those who have built or at least completed welding - how do you ensure alignment of the various components such as shroud/trunnion, receiver, and feed mechanism housing to receiver? It seems that even slight misalignment or miss-location of components could cause feed or function problems later. Thanks in advance. The feed setup is easy to get right with some tinkering/tacking. The cage is where it gets real sporty though as welding on one side causes issues that most of the time a similar weld opposite that will most of the time drag it back but not every time. pretty handy heads up on a couple of problem spots.  Failed To Load Title  Failed To Load Title |
Its to late for the boots, save your watch!
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Originally Posted By TZLVredmist: I just got my parts kit in from HK Parts. The kit itself looks REAL NICE! However...... It was missing the entire buttstock/recoil/buffer assembly.  Sent COMS to HK parts, lets see what happens.Will post pics of kit later. Did you find the stock parts you were missing ? If not message me.. Also i sent both of my damaged Shrouds and that spare broken Stock assembly out to - *Desert Yankee* on HK PRO They will all be back next week or so. His work on my damaged parts is no less than STELLAR and his price for the work was more than reasonable. ill post pics of it all and a quick review when they get back. |
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Originally Posted By barbcue: Did you find the stock parts you were missing ? If not message me.. Also i sent both of my damaged Shrouds and that spare broken Stock assembly out to - *Desert Yankee* on HK PRO They will all be back next week or so. His work on my damaged parts is no less than STELLAR and his price for the work was more than reasonable. ill post pics of it all and a quick review when they get back. Originally Posted By barbcue: Originally Posted By TZLVredmist: I just got my parts kit in from HK Parts. The kit itself looks REAL NICE! However...... It was missing the entire buttstock/recoil/buffer assembly. Sent COMS to HK parts, lets see what happens.Will post pics of kit later. Did you find the stock parts you were missing ? If not message me.. Also i sent both of my damaged Shrouds and that spare broken Stock assembly out to - *Desert Yankee* on HK PRO They will all be back next week or so. His work on my damaged parts is no less than STELLAR and his price for the work was more than reasonable. ill post pics of it all and a quick review when they get back. I did yes! Thanks for the offer of help on it. HK Parts made it all good. |
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I can figure this out on my own, but I’m interested in hearing about best practices for how some of you have mounted the saw box adapter on your 21. Attached File Attached File Attached File |
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Originally Posted By 7insert: Reviewed a half dozen of these kits 4/6 were modded by the portugese to feed disintegrating links. Worth checking if yours is modified. Originally Posted By TZLVredmist: Yup, Mine was modded, the star wheels are obviously more pointy. How can you tell? |
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Originally Posted By Type7SOT: How can you tell? Originally Posted By Type7SOT: Originally Posted By 7insert: Reviewed a half dozen of these kits 4/6 were modded by the portugese to feed disintegrating links. Worth checking if yours is modified. Originally Posted By TZLVredmist: Yup, Mine was modded, the star wheels are obviously more pointy. How can you tell? I think this points it out a bit. Uzi did a video showing a comparison  Failed To Load Title |
Its to late for the boots, save your watch!
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Welp…she’s finished. Attached File Attached File Attached File |
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Originally Posted By cms81586: Welp…she’s finished. https://www.ar15.com/media/mediaFiles/2980/IMG_7798_jpeg-3464338.JPG https://www.ar15.com/media/mediaFiles/2980/IMG_7806_jpeg-3464339.JPG https://www.ar15.com/media/mediaFiles/2980/IMG_7810_jpeg-3464344.JPG Looks excellent! Did you do anything for the inside of the receiver to keep it from rusting? |
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Originally Posted By Type7SOT: Looks excellent! Did you do anything for the inside of the receiver to keep it from rusting? Originally Posted By Type7SOT: Originally Posted By cms81586: Welp…she’s finished. https://www.ar15.com/media/mediaFiles/2980/IMG_7798_jpeg-3464338.JPG https://www.ar15.com/media/mediaFiles/2980/IMG_7806_jpeg-3464339.JPG https://www.ar15.com/media/mediaFiles/2980/IMG_7810_jpeg-3464344.JPG Looks excellent! Did you do anything for the inside of the receiver to keep it from rusting? Noice! |
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Originally Posted By cms81586: I started with spraying the inside of the receiver. I’m sure I didn’t get every bit of bare metal, but I can hit it with a small model airbrush in the future if I think it’ll be an issue. Parkerizing is the way to go. Even as large as the receiver/shroud is it’s doable for not a lot of cash. |
Its to late for the boots, save your watch!
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Originally Posted By kells81: Parkerizing is the way to go. Even as large as the receiver/shroud is it’s doable for not a lot of cash. Eh…I’m not too terribly worried about it. It’s not going to be submerged in salt water for amphibious landings and dragged around in the rain for weeks on end. But yes…you’re correct. |
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Originally Posted By Type7SOT: How can you tell? The video from uzi posted explains what the difference looks like. If you want to confirm and have access to loaded belts/links If you havent assembled the kit, take your feed components and the receiver section that holds them. Assemble them. Load a belt, look through top and and see if it presents the rounds centered in the feed tray/top plate. If you have assembled kit. Lock it open. Load a belt and check thru ejection port that round is centered. |
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A little time in the shop working through a couple of these. The second one coming up really threw me for a loop trying to get the cage tacked on because it wasnt clear but finally figured out the top of the cocking tube channel had a smidge of a dent binding the carrier. Figured out what was up with my welder and started cleaning up the first one I built. It still has some welds that need attention but its much better now that I actually have argon flowing. 
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Its to late for the boots, save your watch!
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They came out great. Nice work. |
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What fastener setup did you end up using on the cryostructure(?) magwell adapter? |
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Originally Posted By 7insert: The video from uzi posted explains what the difference looks like. If you want to confirm and have access to loaded belts/links If you havent assembled the kit, take your feed components and the receiver section that holds them. Assemble them. Load a belt, look through top and and see if it presents the rounds centered in the feed tray/top plate. If you have assembled kit. Lock it open. Load a belt and check thru ejection port that round is centered. I fired half a belt today just to confirm mine would work with M13 links…. It does! Attached File |
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Originally Posted By cms81586: 8-32 x 1/2” hex cap screws. Originally Posted By cms81586: 8-32 x 1/2” hex cap screws. And presumably you drilled and tapped those holes, yeah? Originally Posted By cms81586: I fired half a belt today just to confirm mine would work with M13 links…. It does! Nice. It is worth noting that the increased drag on the M13 will slow the operating system, if running a new locking piece thats lower pressure id make sure it works with your weakest 308 and m13 links to ensure you dont run out of ass. |
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Originally Posted By 7insert: And presumably you drilled and tapped those holes, yeah? Nice. It is worth noting that the increased drag on the M13 will slow the operating system, if running a new locking piece thats lower pressure id make sure it works with your weakest 308 and m13 links to ensure you dont run out of ass. Yeah drilled and tapped. Easy peasy on the drill press. And I’m still on the original locking piece. I also bought one of the NOS FMP locking pieces HKParts had a few of. Planning on buying an RCM #17 36* LP too…that one might have issues with links. We’ll see. Appreciate the tip though. |
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Originally Posted By cms81586: Yeah drilled and tapped. Easy peasy on the drill press. And I’m still on the original locking piece. I also bought one of the NOS FMP locking pieces HKParts had a few of. Planning on buying an RCM #17 36* LP too…that one might have issues with links. We’ll see. Appreciate the tip though. So mine with fresh springs throughout wont run on a 36 deg locking piece on belts or links. Even after being run in for a couple hundred at this point. I went with an RCM #9 40* LP and it is extremely tame and mild. Im keeping the 36deg for suppressor usage but thats it. |
| Interesting. I bought a new recoil spring but it’s sitting in a box as a spare for if I ever notice the buffer getting beat to hell. I’m interested in seeing how it runs with the 36* now. I need to find a suppressor mount in this thread pitch for my old AAC can to see how it runs. |
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Originally Posted By cms81586: Interesting. I bought a new recoil spring but it’s sitting in a box as a spare for if I ever notice the buffer getting beat to hell. I’m interested in seeing how it runs with the 36* now. I need to find a suppressor mount in this thread pitch for my old AAC can to see how it runs. I'd 100% swap the recoil spring. I was doing some ROF testing and mine was cooked, swapping spring slowed it down fairly nicely. |
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Originally Posted By Marksman14: This may be the coolest thread on this forum. I wish I had the skills you guys have. There's zero chance I'd be able to manage anything close to this. You'd be surprised what you can accomplish if you give yourself the chance to try |
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Originally Posted By TZLVredmist: I have an opportunity to snag an MG3 AA Tripod here local. I figure it would work well for displaying this gun taking up less room! Anyone else done this yet? I assume I need an adaptor. If you have the option to get an AA tripod locally you should, people are crazy with the pricing they want for them online. I accidentally bought 4 at an auction a couple years ago because of this  Michaels Machine makes an adapter that slips onto it and locks into the bipod interface, If you want a drum holder you will be limited to the front bipod interface so make sure you are careful when you let go of the gun. For display purposes you'd need some sort of shims or a wire from ceiling since everything on an MG3 AA tripod just wants to face the sky completely vertical. |
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Originally Posted By 7insert: If you have the option to get an AA tripod locally you should, people are crazy with the pricing they want for them online. I accidentally bought 4 at an auction a couple years ago because of this Michaels Machine makes an adapter that slips onto it and locks into the bipod interface, If you want a drum holder you will be limited to the front bipod interface so make sure you are careful when you let go of the gun. For display purposes you'd need some sort of shims or a wire from ceiling since everything on an MG3 AA tripod just wants to face the sky completely vertical. Alright perfect! |
If you bought an HK-21 kit get in here! (Now a build thread…) (Page 13 of 17)
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