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MP, USA
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Posted: 6/28/2024 8:29:04 PM EDT
[#1]
Quote HistoryOriginally Posted By Type7SOT: Got the trunnion out. Is there any way to verify that this trunnion is servicable before completely assembling the gun? https://www.ar15.com/media/mediaFiles/490765/1000006611_jpg-3252995.JPG Pop a barrel and bolt group in, Check bolt gap. |
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Posted: 6/28/2024 9:12:38 PM EDT
[#2]
Quote HistoryOriginally Posted By JoshNC: Pop a barrel and bolt group in, Check bolt gap. I would if I had a barrel lol |
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MP, USA
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Posted: 6/28/2024 11:39:39 PM EDT
[Last Edit: JoshNC]
[#3]
Quote HistoryOriginally Posted By Type7SOT: I would if I had a barrel lol I have a brand new and a used FMP barrel. If you want to send me your trunion and bolt group, I’ll check it out with my barrels and send them back. |
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Posted: 6/29/2024 6:17:10 PM EDT
[#4]
Quote HistoryOriginally Posted By JoshNC: I have a brand new and a used FMP barrel. If you want to send me your trunion and bolt group, I’ll check it out with my barrels and send them back. Got your pm, I may take you up on that. I want to do some more tinkering first but I'll let you know. Thanks! |
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Posted: 6/29/2024 6:48:32 PM EDT
[#5]
Got a PTR receiver and hacked the magwell off, and dry fit everything together. Still need to do some fitting, but at least I have something to look at!
 Attached File |
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CA, USA
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Posted: 6/29/2024 7:08:19 PM EDT
[#6]
OK- "links and belts"
Will these older HK21's run off of M13 and DM6 links or are they DM1 belt friendly only ? And if they will , are the DM6 links an upgrade over the M13 links ? Also will crank loaders that work with M13 links also work with DM6 links ? |
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Posted: 6/29/2024 9:31:31 PM EDT
[#7]
I don’t think the 21’s are supposed to run M13 or DM6 links but I’ve read that people have had some limited success.
I think it’s RDTS or one of the other builders that can cut some relief on your feed sprocket so they do run smooth. The links are spaced closer together than the belt, so I think they trim a bit off the back side of the sprocket “tooth”. That’s what I’ve been able to glean over the last few weeks since buying one of these kits. I have no experience with the 21’s but the MG-3 has some of the same issues and I have dealt with that recently. |
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Posted: 6/30/2024 8:29:19 AM EDT
[Last Edit: Type7SOT]
[#8]
According to guys on Weapons Guild, you can use these A3 stock rails as reiforcement rails. Just ordered a set:
https://www.robertrtg.com/store/pc/RIGHT-LEFT-A3-STOCK-RAILS-FOR-G3-COLLAPSIBLE-NEW-GERMAN-2p7001.htm Also while your placing an order you can also get a rear sight base, semi auto shelf, and 50 round belts. |
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Posted: 7/2/2024 6:20:08 PM EDT
[#9]
With everything dry fit together, there is about a 1/4" gap between the barrel shroud and the feedbox. I believe this is due to agressive demilling, and shouldnt be an issue other than cosmetically. Anyone else seeing this?
 Attached File |
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Posted: 7/2/2024 6:36:39 PM EDT
[#10]
I haven’t got that far but was expecting something similar. They cut a significant bit of material off the backend of my feed boxes as well, you can see by how narrow the strip of metal aft of the ejection port is compared to a factory gun.
I’m guessing it’s no problem at all but I’m unsure of how to precisely locate the feed mechanism with respect to the trunion. The only thing that would put it in the wrong place would be an out of spec flat I guess. |
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Posted: 7/2/2024 7:23:36 PM EDT
[#11]
Quote HistoryOriginally Posted By BASE: I haven’t got that far but was expecting something similar. They cut a significant bit of material off the backend of my feed boxes as well, you can see by how narrow the strip of metal aft of the ejection port is compared to a factory gun. I’m guessing it’s no problem at all but I’m unsure of how to precisely locate the feed mechanism with respect to the trunion. The only thing that would put it in the wrong place would be an out of spec flat I guess. My plan was to install the grip housing and the stock, stock pins, and then tap the whole assembly rearward as far as it can go. I think thats the correct location but not 100% sure. One thing to be careful for non SOT's is having everything welded up before installing the semi shelf, you dont want to inadvertantly create a MG. I plan to use the front pin to help locate the feed box, tack a few welds up, then immediately weld the semi shelf on. |
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Posted: 7/3/2024 12:05:03 AM EDT
[Last Edit: cms81586]
[#12]
Quote HistoryOriginally Posted By Type7SOT: With everything dry fit together, there is about a 1/4" gap between the barrel shroud and the feedbox. I believe this is due to agressive demilling, and shouldnt be an issue other than cosmetically. Anyone else seeing this? https://www.ar15.com/media/mediaFiles/490765/1000006665_jpg-3256423.JPG What’s the diameter of the receiver there? Might be worth buying some aluminum round stock to use as a heat sink/backer and build up the material there with passes of weld to fill the gap. Would take a bit of time but would definitely fill the gap. The feed box length should be 4.7” front to rear. |
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Posted: 7/3/2024 6:07:17 AM EDT
[#13]
Quote HistoryOriginally Posted By cms81586: What’s the diameter of the receiver there? Might be worth buying some aluminum round stock to use as a heat sink/backer and build up the material there with passes of weld to fill the gap. Would take a bit of time but would definitely fill the gap. The feed box length should be 4.7” front to rear. I was thinking the same thing, except I dont think I need the aluminum round stock because the trunnion will be installed at that point. |
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Posted: 7/3/2024 7:04:51 AM EDT
[#14]
I'm considering adding a bit of material to mine, just to make it look right. Probably opening to door to more trouble than it's worth to correct a minor cosmetic issue. I have a 1.67" dia piece of aluminum that I turned to use as a heat sink and some 16 ga metal cut and bent up. I was going to weld excess material on using the aluminum backup/heatsink and then cut down to size.
I don't think there is any real structural advantage to filling in the gap though. I've been having second thoughts as I can imagine how dumb I'll feel after I blow a big hole through that sheetmetal box trying to fix a non-issue... |
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Posted: 7/3/2024 12:21:08 PM EDT
[Last Edit: Type7SOT]
[#15]
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Posted: 7/3/2024 4:49:08 PM EDT
[Last Edit: Type7SOT]
[#16]
Does anyone have any thoughts on where to drill the plug welding holes for the trunnion?
On my original trunnion, I can see there were 6 plug welds, 3 on each side. On my PTR receiver, there are 2 pre-drilled holes, but they do not line up with any of the 6 holes on the original hk21. So I cannot emulate the same 6 hole pattern unless I fill in the factory 2 holes in the PTR receiver. I'm not crazy about that option. When I look at the weapons guild thread, I see they used a very different hole pattern. It looks like the used the original PTR holes, and added additional holes in various locations. I am probably overthinking this whole thing, but I wanted to ask here before I started drilling holes in my good receiver. Any thoughts? Edit: I decided that I am indeed overthinking it, and went with this:  Attached File Attached File |
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Posted: 7/3/2024 6:30:33 PM EDT
[#17]
I have all the fitting done and everything dry fit together, including the trunnion and bolt. Everything function tests good! Now I just need the reinforcing rails which are on the way.
 Attached File |
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IL, USA
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Posted: 7/3/2024 8:12:59 PM EDT
[#18]
can any of you show the cut pattern of the receiver clearly?
dimensions/guidance? |
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Posted: 7/3/2024 8:14:20 PM EDT
[#19]
The adjustment knob on my rear sight fell off. It seems to be a press fit, but wasnt very tight. It twisted right off trying to adjust the sight.
Rather than complain to centerfire systems, I welded it back on   Attached File Attached File |
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Posted: 7/3/2024 8:16:32 PM EDT
[#20]
Quote HistoryOriginally Posted By handym3000: can any of you show the cut pattern of the receiver clearly? dimensions/guidance?  Attached File Attached File |
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USA
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Posted: 7/3/2024 8:18:47 PM EDT
[Last Edit: Heineken]
[#21]
Picked up an mg3 belt loader today...I got all the accessories now...just need the gun
 https://youtu.be/IEjyBuVyVEo?si=IJCQAGu-I9BrvpMk |
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Posted: 7/3/2024 8:59:47 PM EDT
[#22]
Quote HistoryOriginally Posted By handym3000: can any of you show the cut pattern of the receiver clearly? dimensions/guidance? There’s a pdf guide posted over at weapons guild but I don’t think you need that. Looks like HK just trimmed it up to the bottom of the rail. Seems like the feed stud at the back would be the highest point but straight across under the rail seems to work fine. |
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CA, USA
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Posted: 7/3/2024 10:11:04 PM EDT
[Last Edit: barbcue]
[#23]
Got my kits from Atlantic Firearms noticed one of them that the Triple Frame front site RING is slightly "ovaled" is this an easy fix for a builder ?
or should i send it back for one that is not out of round ? |
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Posted: 7/3/2024 10:27:32 PM EDT
[Last Edit: BASE]
[#24]
I think that is somewhat common. Or I'm very unlucky. I just straightened out a G3 front sight by removing the blade and pounding a tapered punch into it. Was a little afraid it might crack but it didn't.
FYI: both my shroud cocking tubes were somewhat smashed when I got them and 3/4" cold rolled pounded into them worked really well. I spent a few hours bumping out dents and demilling kits last night. |
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CA, USA
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Posted: 7/4/2024 12:00:04 AM EDT
[#25]
Quote HistoryOriginally Posted By BASE: I think that is somewhat common. Or I'm very unlucky. I just straightened out a G3 front sight by removing the blade and pounding a tapered punch into it. Was a little afraid it might crack but it didn't. FYI: both my shroud cocking tubes were somewhat smashed when I got them and 3/4" cold rolled pounded into them worked really well. I spent a few hours bumping out dents and demilling kits last night. Thanks Base ! Ive got the next 5 days off so ill get these spread out and take some pics of the Atlantic kits. As it stands- the out of round site is my only real complaint they look pretty damn good over all imo. |
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IL, USA
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Posted: 7/4/2024 4:43:49 PM EDT
[#26]
I get that the trimming is key.
I was looking more for pictures here and confirmation of what dimensions we should use. I generally want to confirm that 1 source is correct. maybe some rough ruler checks in the pics. We had mentioned earlier that this was going to be like a build guide. this is a ton of cash to build, but before i go nuts and drop this kind of coin in wanting to make sure it can be done. |
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Posted: 7/4/2024 6:54:47 PM EDT
[Last Edit: barbcue]
[#27]
So my kits came with a few little tiny steel pins that look to be like oversized ZIPPO lighter flints. In all the pictures of these kits these little pins are not shown.
thing is- One kit came with 3 The other kit came with 1 Any idea what they are? locking lever pins ? Barrel pins ? Barrel "grip" pins ? Have no idea.. how many they should come with ? |
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Posted: 7/4/2024 8:32:21 PM EDT
[#28]
Quote HistoryOriginally Posted By handym3000: I get that the trimming is key. I was looking more for pictures here and confirmation of what dimensions we should use. I generally want to confirm that 1 source is correct. maybe some rough ruler checks in the pics. We had mentioned earlier that this was going to be like a build guide. this is a ton of cash to build, but before i go nuts and drop this kind of coin in wanting to make sure it can be done. I have taken zero measurements so far. Just fitting things together, marking, and trimming. If you take your time it becomes obvious where you need to cut. |
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Posted: 7/4/2024 10:45:59 PM EDT
[Last Edit: barbcue]
[#29]
Other than the bent site ring- looking these over again, i noticed that the bottom of the cocking tub slot on one of my Shrouds is slightly bent outwards towards the front. How hard would it be for a builder to straighten this out ?
(Anyways full kit pics tomorrow)  Attached File |
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Posted: 7/4/2024 11:04:59 PM EDT
[#30]
That looks like an easy fix in my opinion. I had to hammer a dent out of my shroud, took all of 3 minutes.
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Posted: 7/4/2024 11:39:30 PM EDT
[#31]
Quote HistoryOriginally Posted By Type7SOT: That looks like an easy fix in my opinion. I had to hammer a dent out of my shroud, took all of 3 minutes. Thanks Type7 ! |
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Posted: 7/5/2024 12:20:15 PM EDT
[#32]
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Posted: 7/5/2024 12:25:07 PM EDT
[Last Edit: barbcue]
[#33]
Heres where i ran into problems
Recoil spring was bent during shipping on one kit and it broke the back plate  Attached FileSame kit the shroud has a broken sling mount (bottom shroud)  Attached FileSame kit the triple frame is "out of round"  Attached Filei sent an email to atlantic to see how they want to proceed.. id be happy with a stock and recoil spring swap and a shroud swap. on the one kit other kit had the slightly bent cocking handle slot but i can live with that as im betting that an easy fix. |
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Posted: 7/5/2024 12:26:59 PM EDT
[#34]
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Posted: 7/5/2024 4:40:43 PM EDT
[Last Edit: barbcue]
[#35]
a few more pictures of the Atlantic Parts.
KIT 1  Attached File Attached FileKIT 2  Attached File Attached FileRTG has the 21 triple frame and the 21 sling mount in stock im considering just ordering those and keeping the shroud UPDATE- Just ordered the triple frame (actually ordered a pair of these ill have them both swapped out) and the sling mount - only worry now is the rivets holding the sling mount on, hoping those are easy to source or the ones on it now can be reused. |
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Posted: 7/5/2024 6:22:39 PM EDT
[#36]
That kit looks really clean. Very little wear and the finish is still dark.
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Posted: 7/5/2024 7:11:58 PM EDT
[Last Edit: barbcue]
[#37]
Quote HistoryOriginally Posted By Type7SOT: That kit looks really clean. Very little wear and the finish is still dark. Overall im super happy so far with BOTH kits 1. Atlantic swaps out the stock/backplate and recoil rod for a working set. 2. The builder (MM) straightens out that cocking tube slot on the other shroud. 3. Along with $150 in parts and a few rivets to get the one Shroud back where it should be. (OEM German parts already ordered) I think i did ok ! |
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Posted: 7/5/2024 7:23:06 PM EDT
[#38]
As a point of comparison, here is my feedbox:
 Attached FileThe finish is worn completely through. Fortunately, it appears to only be the finish. The base metal does not show any wear. It should be structurally and dimensionally good still, but I'm going to parkerize it to protect it from corrosion and make it look nice. |
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Posted: 7/5/2024 7:32:04 PM EDT
[Last Edit: barbcue]
[#39]
Quote HistoryOriginally Posted By Type7SOT: As a point of comparison, here is my feedbox: The finish is worn completely through. Fortunately, it appears to only be the finish. The base metal does not show any wear. It should be structurally and dimensionally good still, but I'm going to parkerize it to protect it from corrosion and make it look nice. Yes your finish is totally gone, but the metal looks to be sound from here. I see what you mean. I was fortunate on overall "wear and tear" on my pair of kits a few small problems but overall solid condition. I think im the first to post any of these from Atlantic Firearms ANYWHERE ? - So with a sample size of 2 kits i think we can say so far the Atlantic kits are pretty nice (NOW lets see how they deal with replacing my stock and recoil rod) Seems like other vendors selling these are stepping up SOLID in replacing bad parts will post on their CS as soon as they respond again. Which leads to a question - I wonder how many spare parts Century imported with these kits? Also wonder what will become of the all the barrels ? With the Chevron verdict is it possible we will see the original barrels to these kits at some point ? UPDATE ::-- Atlantic is sending me replacement parts so their CS on these kits is good to go ! Thanks Atlantic Firearms ! |
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Posted: 7/5/2024 8:41:48 PM EDT
[Last Edit: barbcue]
[#40]
Currently these Kits from:
Atlantic Firearms Apex Century Are all out of stock. Only place i see that still has any left at the moment is Centerfire. |
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MP, USA
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Posted: 7/5/2024 9:46:49 PM EDT
[#41]
Quote HistoryOriginally Posted By barbcue: Currently these Kits from: Atlantic Firearms Apex Century Are all out of stock. Only place i see that still has any left at the moment is Centerfire. Centerfire is showing in stock, but when you click on the link it shows “preorder”. |
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Posted: 7/5/2024 9:52:24 PM EDT
[#42]
Quote HistoryOriginally Posted By barbcue: a few more pictures of the Atlantic Parts. KIT 1 https://www.ar15.com/media/mediaFiles/16380/449165183_434130359524876_91201810271458-3259076.JPG https://www.ar15.com/media/mediaFiles/16380/449701775_1187532692260104_1673108013240-3259077.JPG KIT 2 https://www.ar15.com/media/mediaFiles/16380/449343015_493137289928428_12528160672233-3259078.JPG https://www.ar15.com/media/mediaFiles/16380/449160271_982426757001296_13228843227106-3259094.JPG RTG has the 21 triple frame and the 21 sling mount in stock im considering just ordering those and keeping the shroud UPDATE- Just ordered the triple frame (actually ordered a pair of these ill have them both swapped out) and the sling mount - only worry now is the rivets holding the sling mount on, hoping those are easy to source or the ones on it now can be reused. My kit doesn’t have these holes…  Attached File |
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Posted: 7/5/2024 10:00:46 PM EDT
[Last Edit: barbcue]
[#43]
Quote HistoryOriginally Posted By cms81586: My kit doesn’t have these holes… Great Another MYSTERY ! Might have something to do with mounting a feed box ? I have no idea. |
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MP, USA
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Posted: 7/5/2024 10:54:26 PM EDT
[Last Edit: JoshNC]
[#44]
Quote HistoryOriginally Posted By barbcue: Great Another MYSTERY ! Might have something to do with mounting a feed box ? I have no idea. Quote HistoryOriginally Posted By barbcue: Originally Posted By cms81586: My kit doesn’t have these holes… Great Another MYSTERY ! Might have something to do with mounting a feed box ? I have no idea. The holes are for retention of the mag adapter to make it an 11. There are two types of mag adapters, one from HK and one from FMP. |
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Posted: 7/5/2024 10:55:56 PM EDT
[Last Edit: barbcue]
[#45]
Quote HistoryOriginally Posted By JoshNC: The holes are for retention of the mag adapter to make it an 11. There are two types of mag adapters, one from HK and one from FMP. Thanks Josh ! Anyone have any idea where to source the FMP version of the mag adapters ? |
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Posted: 7/5/2024 11:15:28 PM EDT
[Last Edit: Type7SOT]
[#46]
So, I stripped my feedbox and parkerized it. Getting it back together may be a bitch though!
 Attached File Attached File Attached File |
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MP, USA
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Posted: 7/5/2024 11:16:14 PM EDT
[Last Edit: JoshNC]
[#47]
Quote HistoryOriginally Posted By barbcue: Thanks Josh ! Anyone have any idea where to source the FMP version of the mag adapters ? The mag adapters are not easily sourced. I lucked into one last year. They occasionally popped up on HK Pro, but I suspect that’s a thing of the past with the release of these kits. Honestly, it’s not worth shooting a 21 with a mag. Discussion on HKPro |
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Posted: 7/5/2024 11:54:15 PM EDT
[Last Edit: barbcue]
[#48]
Quote HistoryOriginally Posted By Type7SOT: So, I stripped my feedbox and parkerized it. Getting it back together may be a bitch though! Looks Good Type7 ! |
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Posted: 7/7/2024 7:22:23 PM EDT
[#49]
Somehow I got this thing back together. I do NOT recommend taking this apart if you can avoid it!
 Attached File |
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Posted: 7/7/2024 7:53:15 PM EDT
[Last Edit: Type7SOT]
[#50]
A3 stock rails cut down. First step in converting them to reinforcing rails. These are very hard.
 Attached File Attached File |
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