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Posted: 8/13/2024 10:26:00 PM EDT
[#1]
This is an awesome thread.
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Posted: 8/14/2024 12:24:56 PM EDT
[#2]
I bet it gets a lot more awesome once the new 21 barrels start shipping.
RCM posted a pic of a bin of CHF blanks that had been profiled a couple weeks back. I think Cryostructures is at about the same stage I believe but theirs should be going out for chrome after. |
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Posted: 8/18/2024 1:04:45 PM EDT
[#3]
Anyone know where to find one of these in stock? Or have a drawing?
https://hkparts.net/all-parts/hkp-semi-shelf-weldment-metal-grip-housing/ |
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Posted: 8/18/2024 7:55:39 PM EDT
[#4]
Quote HistoryOriginally Posted By Type7SOT: Anyone know where to find one of these in stock? Or have a drawing? https://hkparts.net/all-parts/hkp-semi-shelf-weldment-metal-grip-housing/ Not sure…but the way the SEF lowers are cut at the front I think you could just use the trigger pack to interface with the semi shelf on the feed box. |
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Posted: 8/18/2024 8:03:01 PM EDT
[Last Edit: Type7SOT]
[#5]
Quote HistoryOriginally Posted By cms81586: Not sure…but the way the SEF lowers are cut at the front I think you could just use the trigger pack to interface with the semi shelf on the feed box. Thats what I thought too. But I'm at that point of the build and it appears you need this block in the trigger housing.  Attached File Attached File Attached FileAs it stands, there is nearly 1/4" of up and down play in the front of the grip housing. For reference:  Attached File |
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Posted: 8/18/2024 8:15:25 PM EDT
[#6]
I’d shim the trigger box personally, but that should be easy enough to make if you wanted. Sorry I can be more help. You’re a bit ahead of me. I was waiting on my semi trigger pack to arrive tomorrow before I kept going.
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Posted: 8/18/2024 8:22:26 PM EDT
[#7]
Heres how the plastic grip housings look, before and after clipping and pinning:
 Attached FileThis should demonstrate why that block is needed for the metal ones but not the plastic ones. The plastic grip housings already have a steel insert, it just needs to be milled out a bit. The metal grip housings are wide open. If I "shim" the trigger pack, the shim would be 3/16 to 1/4" thick. I think I might just weld a block in there. Or get a navy lower. Hmmmm |
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Posted: 8/18/2024 10:02:53 PM EDT
[Last Edit: BASE]
[#8]
I’ve seen the metal ones done where the ears are partially milled away like the plastic ones. I think Parabellum and Bill Springfield offer that service.
There are some pics on Jeff's website of what I'm talking about: https://parabellumcombatsystemsllc.com/product/metal-lower/ I was thinking I'd try welding a thin bar across the front to sit on the shelf as well as milling the ears back. I've not gotten there quite yet though. |
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MP, USA
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Posted: 8/19/2024 8:02:25 AM EDT
[#9]
Quote HistoryOriginally Posted By Type7SOT: Thats what I thought too. But I'm at that point of the build and it appears you need this block in the trigger housing. https://www.ar15.com/media/mediaFiles/490765/1000007256_jpg-3298204.JPG https://www.ar15.com/media/mediaFiles/490765/1000007258_jpg-3298205.JPG https://www.ar15.com/media/mediaFiles/490765/1000007259_jpg-3298206.JPG As it stands, there is nearly 1/4" of up and down play in the front of the grip housing. For reference: https://www.ar15.com/media/mediaFiles/490765/1000007257_jpg-3298213.JPG I would just buy a g3 navy contour SEF plastic housing and modify it to fit your shelf. They have more steel up front to make it fit tightly on the shelf. |
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Posted: 8/19/2024 6:38:00 PM EDT
[#10]
Quote HistoryOriginally Posted By JoshNC: I would just buy a g3 navy contour SEF plastic housing and modify it to fit your shelf. They have more steel up front to make it fit tightly on the shelf. I just did exactly that. I actually went with a pre-clipped and pinned one. Hopefully the shelf lines up, I measured mine very carefully when welding and it's within .002" according to a drawing I found. I think the navy lower will look real nice with my clubfoot stock. Like a poor mans 21E 
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Posted: 8/19/2024 8:25:13 PM EDT
[#11]
Quote HistoryOriginally Posted By Type7SOT: I just did exactly that. I actually went with a pre-clipped and pinned one. Hopefully the shelf lines up, I measured mine very carefully when welding and it's within .002" according to a drawing I found. I think the navy lower will look real nice with my clubfoot stock. Like a poor mans 21E Yup…after looking at everything that’s the route I’m taking…and I did the same thing with the clubfoot stock.  Attached File |
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Posted: 8/19/2024 8:33:29 PM EDT
[#12]
Quote HistoryOriginally Posted By cms81586: Yup…after looking at everything that’s the route I’m taking…and I did the same thing with the clubfoot stock. https://www.ar15.com/media/mediaFiles/2980/IMG_3715_jpeg-3299185.JPG  Dont forget we'll need to trim the upper ears off the navy packs to clear the belt feed mech, but should be pretty easy with a belt sander. |
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TX, USA
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Posted: 8/19/2024 11:34:55 PM EDT
[#13]
This thread is awesome. Can't wait to get mine built.
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USA
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Posted: 8/22/2024 6:54:56 PM EDT
[#14]
I'm dying....mine is off being built and I got all these accessories and belts and belt loader and tripod and extra barrel...the wait is killing me
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USA
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Posted: 8/22/2024 6:58:37 PM EDT
[Last Edit: Heineken]
[#15]
Quote HistoryOriginally Posted By BASE: I’ve seen the metal ones done where the ears are partially milled away like the plastic ones. I think Parabellum and Bill Springfield offer that service. There are some pics on Jeff's website of what I'm talking about: https://parabellumcombatsystemsllc.com/product/metal-lower/ I was thinking I'd try welding a thin bar across the front to sit on the shelf as well as milling the ears back. I've not gotten there quite yet though. I have seen some that they just milled the metal ears and there is just a tiny bit of material left that sits on the shelf, it works but it's not optimal. Welding in a piece is the correct way. HK parts sells the exact weldment made for that...but of course they are out of stock with no known ETA....but you can just make your own. Also as others said you can just use a plastic SEF g3 lower as well and c&p the front as normal...i like the metal lower look though 
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Posted: 8/23/2024 5:27:26 PM EDT
[#16]
 Attached FileClipped and pinned SEF Navy lower installed. It took a good amount of fitting on both the lower AND the gun. Clearly the HK21 was not designed to work with a polymer lower because there is interference with the feed box. The sheetmetal lower fits better because its thinner. Ill try to get pics later showing what I'm talking about. But anyway, seems to work if you modify some things, and looks great! |
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TX, USA
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Posted: 8/24/2024 10:22:45 AM EDT
[#17]
Does anyone have a good contact at Atlantic? My kit came in the other day and the feed box is mangled on the top right side ears. I've asked more experienced builders, they say it *might* be salvageable. One side is bent inwards, other side looks like a bullet went through from the inside and peeled back a huge chunk of steel folded towards the front. It was very hastily demilled, carelessly even.
Regarding previous posts on semi shelf weldments for metal housings, I've made them from bar stock with good results. Its not very difficult to make, depending how you weld the shelf on the receiver will dictate the height of your corresponding latch. |
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USA
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Posted: 8/24/2024 12:19:53 PM EDT
[#18]
The plastic SEF with the clubfoot looks HOT! Can't wait to see that all finished!!!
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Posted: 8/24/2024 7:43:14 PM EDT
[Last Edit: TZLVredmist]
[#19]
BUTTS!
I was browsing HK UMP conversion info this morning and ran across this thread. PURCHASED: HK21 Parts Kit Two G3 Flats Bending Jig Weldment Parts Set Reinforcing T-Rails |
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Posted: 8/25/2024 9:59:37 AM EDT
[#20]
Are more kits coming in or are they all gone?
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Posted: 8/25/2024 10:16:27 AM EDT
[#21]
Quote HistoryOriginally Posted By RedFox1911: Are more kits coming in or are they all gone? Apex had a second batch with a slightly different demill: https://www.apexgunparts.com/hk21-belt-fed-parts-kit-7-62-nato-308-good-d.html |
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Posted: 8/26/2024 8:46:40 AM EDT
[#22]
I heard RCM was getting pretty close with the barrels they are making. I also thought the cryo barrels were supposed to be shipping a while back. Has anyone seen one yet?
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Posted: 8/26/2024 1:38:26 PM EDT
[#23]
Quote HistoryOriginally Posted By BASE: I heard RCM was getting pretty close with the barrels they are making. I also thought the cryo barrels were supposed to be shipping a while back. Has anyone seen one yet? I have two coming from Cryo. They are supposedly shipping at the end of the month according to the website. I ordered two sets of rails this weekend, and they already have a shipping label. |
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Posted: 8/26/2024 1:44:41 PM EDT
[#24]
I thought there was a previous batch that was supposed to have gone out already, maybe not though.
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Posted: 8/26/2024 6:34:51 PM EDT
[#25]
Anyone thinking about giving Cryostructure money should google "shadow ops weaponry paul russ"
According to thread on HK Pro, its the same guy. |
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Posted: 8/26/2024 8:08:31 PM EDT
[#26]
Quote HistoryOriginally Posted By Type7SOT: Anyone thinking about giving Cryostructure money should google "shadow ops weaponry paul russ" According to thread on HK Pro, its the same guy. That’s what credit cards are for. If they don’t deliver as the 90 day dispute window approaches and you can’t get a refund you dispute the charge and walk away. |
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USA
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Posted: 8/27/2024 7:51:56 AM EDT
[#27]
Cryostructure barrels were supposed to go out July 31. He got the blanks in and said they were almost done. Then a week later it was that he was waiting on tooling to cut the chambers or something, then they would go to chrome. Then it was by the end of August...which I'm starting to have doubts. I never understood why some venders do this....give a date they o ow they can't make....then give a new date and miss it, and repeat over and over. I'm in the second cryo batch and if I don't see the first round ship soon I'm ejecting.
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MP, USA
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Posted: 8/27/2024 8:14:11 AM EDT
[Last Edit: JoshNC]
[#28]
Quote HistoryOriginally Posted By Heineken: Cryostructure barrels were supposed to go out July 31. He got the blanks in and said they were almost done. Then a week later it was that he was waiting on tooling to cut the chambers or something, then they would go to chrome. Then it was by the end of August...which I'm starting to have doubts. I never understood why some venders do this....give a date they o ow they can't make....then give a new date and miss it, and repeat over and over. I'm in the second cryo batch and if I don't see the first round ship soon I'm ejecting. They seem to be falling into all of the traps of manufacturing. Taking on too many projects, announcing products that aren’t yet available, taking pre-payment, etc, etc, etc. I truly hope these are great and will buy a bunch if they are. I will not be an early adopter or pre-pay for items with zero track record. RCM has been making 21E and 23E barrels for over a decade and has the specs down pat. I wish they were making theirs chrome lined, but CHF and nitride and 50% of the cost of the cryostructure means one can buy 2x the number of barrels and rotate them. |
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Posted: 8/27/2024 12:29:19 PM EDT
[#29]
Anybody have a builder they are happy with, that is responsive to calls or emails? I have contacted most of the builders mentioned in this thread about having two of the kits built into rifles, and I have heard back from exactly NOBODY. I would have though $10k+ in business would have at least gotten me a return call... but no.
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MP, USA
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Posted: 8/27/2024 6:43:56 PM EDT
[Last Edit: JoshNC]
[#30]
Originally Posted By Debo75: Anybody have a builder they are happy with, that is responsive to calls or emails? I have contacted most of the builders mentioned in this thread about having two of the kits built into rifles, and I have heard back from exactly NOBODY. I would have though $10k+ in business would have at least gotten me a return call... but no. I am sure most builders are overwhelmed with these 21 kits. I’d recommend calling: Michaels Machines http://www.michaelsmachines.com/ Desert Yankee https://www.instagram.com/desert_yankee_?igsh=NTc4MTIwNjQ2YQ== |
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Posted: 8/28/2024 5:55:46 AM EDT
[Last Edit: barbcue]
[#31]
Quote HistoryOriginally Posted By 19Charlie_84: Does anyone have a good contact at Atlantic? My kit came in the other day and the feed box is mangled on the top right side ears. I've asked more experienced builders, they say it *might* be salvageable. One side is bent inwards, other side looks like a bullet went through from the inside and peeled back a huge chunk of steel folded towards the front. It was very hastily demilled, carelessly even. YES, Contact them via email immediately ! Tell them the part you have is simply "unservicable". (CHECK AND MAKE SURE OTHER PARTS ARE TO YOUR LIKING AND "SQUARE" BEFORE YOU EMAIL THEM - you may only get ONE chance at having them replace parts !) I did the same and they quickly sent me a much better condition shroud and buttstock assembly and didnt even want or ask for the original parts back Atlantic was stellar with CS on my 2 kits. "YMMV" |
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Posted: 8/29/2024 6:17:07 PM EDT
[#32]
 My Cryo reciever rails came in today. Some of you guys are almost done, and I am still getting parts together.
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Posted: 8/29/2024 8:19:35 PM EDT
[#33]
Ugh…can’t do shit until I get a barrel.
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Posted: 8/29/2024 9:50:43 PM EDT
[#34]
Quote HistoryOriginally Posted By cms81586: Ugh…can’t do shit until I get a barrel. Yep, I'm stuck too. Everything done but welding the shroud. Cant do that until i have a barrel to check alignment and cocking tube support gap. 
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Posted: 8/30/2024 7:11:55 AM EDT
[#35]
Quote HistoryOriginally Posted By BASE: Apex had a second batch with a slightly different demill: https://www.apexgunparts.com/hk21-belt-fed-parts-kit-7-62-nato-308-good-d.html Quote HistoryOriginally Posted By BASE: Originally Posted By RedFox1911: Are more kits coming in or are they all gone? Apex had a second batch with a slightly different demill: https://www.apexgunparts.com/hk21-belt-fed-parts-kit-7-62-nato-308-good-d.html Those look like good candidates to graft onto vs rebuild. Kinda the same way RJ does the 40/10 builds. |
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Posted: 8/30/2024 2:51:46 PM EDT
[#36]
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. |
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TX, USA
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Posted: 8/30/2024 11:00:45 PM EDT
[#37]
Quote HistoryOriginally Posted By barbcue: YES, Contact them via email immediately ! Tell them the part you have is simply "unservicable". (CHECK AND MAKE SURE OTHER PARTS ARE TO YOUR LIKING AND "SQUARE" BEFORE YOU EMAIL THEM - you may only get ONE chance at having them replace parts !) I did the same and they quickly sent me a much better condition shroud and buttstock assembly and didnt even want or ask for the original parts back Atlantic was stellar with CS on my 2 kits. "YMMV" Unfortunately, they don't have any spare parts on hand. However, dude said if I find one elsewhere they'd reimburse me the cost of a new box. Centerfire Systems is currently going thru a bunch of kits and may have some for spare parts in a couple weeks. Gatewood supply has some listed individually, which I purchased tonight. I like good CS from companies. |
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Posted: 8/30/2024 11:06:36 PM EDT
[#38]
Quote HistoryOriginally Posted By 19Charlie_84: Unfortunately, they don't have any spare parts on hand. However, dude said if I find one elsewhere they'd reimburse me the cost of a new box. Centerfire Systems is currently going thru a bunch of kits and may have some for spare parts in a couple weeks. Gatewood supply has some listed individually, which I purchased tonight. I like good CS from companies. I’d buy a club foot stock. HK Parts has double wound HK21 springs (not 21E springs). |
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Posted: 8/31/2024 8:15:51 AM EDT
[#39]
Quote HistoryOriginally Posted By cms81586: I’d buy a club foot stock. HK Parts has double wound HK21 springs (not 21E springs). Yeah but he still needs the hk21 buffer. |
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Posted: 8/31/2024 8:58:19 AM EDT
[#40]
Pics of my kit, Minus the stock and buffer/spring that never came.
Super nice kit!       
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Posted: 8/31/2024 11:14:27 AM EDT
[Last Edit: kells81]
[#41]
That looks like a nice set of bones to start with.
Side note- has anyone messed with a Binary setup for one of these? |
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USA
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Posted: 8/31/2024 1:20:45 PM EDT
[#42]
Quote HistoryOriginally Posted By kells81: That looks like a nice set of bones to start with. Side note- has anyone messed with a Binary setup for one of these? Or, would these work with a Lee Sporting lower and an FRT? I'm thinking no, but would be so cool. |
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Posted: 8/31/2024 3:22:28 PM EDT
[#43]
Bent, Welded, Trued the bolt through the receiver THAT SUCKED! and test fit on the trunnion.
  
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Posted: 8/31/2024 4:27:47 PM EDT
[#44]
Quote HistoryOriginally Posted By Teller_Ulam: Or, would these work with a Lee Sporting lower and an FRT? I'm thinking no, but would be so cool. I think there is a HK type super safety that would work. |
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Posted: 8/31/2024 7:43:32 PM EDT
[#45]
Quote HistoryOriginally Posted By Type7SOT: I think there is a HK type super safety that would work. Quote HistoryOriginally Posted By Type7SOT: Originally Posted By Teller_Ulam: Or, would these work with a Lee Sporting lower and an FRT? I'm thinking no, but would be so cool. I think there is a HK type super safety that would work. The super safety for sure looks like a solid option. At least for the regular 21 as the AR style grip frame should fit it. |
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TX, USA
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Posted: 8/31/2024 9:12:30 PM EDT
[#46]
Quote HistoryOriginally Posted By Type7SOT: Yeah but he still needs the hk21 buffer. Quote HistoryOriginally Posted By Type7SOT: Originally Posted By cms81586: I’d buy a club foot stock. HK Parts has double wound HK21 springs (not 21E springs). Yeah but he still needs the hk21 buffer. Clubfoot stock, side rails, top pic rail, weldments for receiver, belts, starter tabs, and some other sundries came today and yesterday. Looking at 21E buffer parts on RTG. Need to take stuff apart and clean cosmo and demill chips out. |
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Posted: 8/31/2024 9:24:31 PM EDT
[#47]
Quote HistoryOriginally Posted By Type7SOT: Yeah but he still needs the hk21 buffer. May as well go with a 21E buffer and relocate the cocking handle notch. Not that much more work. |
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Posted: 9/1/2024 5:14:10 AM EDT
[#48]
Quote HistoryOriginally Posted By 19Charlie_84: Unfortunately, they don't have any spare parts on hand. However, dude said if I find one elsewhere they'd reimburse me the cost of a new box. Centerfire Systems is currently going thru a bunch of kits and may have some for spare parts in a couple weeks. Gatewood supply has some listed individually, which I purchased tonight. I like good CS from companies. If its as you say with a bent destroyed box - SEND THAT KIT BACK IMMEDIATELY for a replacement of refund ! |
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Posted: 9/1/2024 7:47:29 AM EDT
[#49]
Quote HistoryOriginally Posted By 19Charlie_84: Does anyone have a good contact at Atlantic? My kit came in the other day and the feed box is mangled on the top right side ears. I've asked more experienced builders, they say it *might* be salvageable. One side is bent inwards, other side looks like a bullet went through from the inside and peeled back a huge chunk of steel folded towards the front. It was very hastily demilled, carelessly even. Regarding previous posts on semi shelf weldments for metal housings, I've made them from bar stock with good results. Its not very difficult to make, depending how you weld the shelf on the receiver will dictate the height of your corresponding latch. Did you manage to get it figured out? I have a spare feed box if you didn’t. |
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TX, USA
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Posted: 9/1/2024 10:27:31 AM EDT
[#50]
Quote HistoryOriginally Posted By cms81586: Did you manage to get it figured out? I have a spare feed box if you didn’t. Ya, ordered a box from Gatewood Supply and sent Atlantic a screenie of the receipt. It was on Friday night so we'll see on Mon morning. I would have sent it back, but they don't have any more to replace. |
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