I have a good friend that bought one of the GSG/ATI mp40 clones in 9mm a while back that started out as a pistol. While he loved shooting it, he hated that he didn't have any way of shouldering the gun and it's really accurate considering you had to kind of just look over the gun while holding it out in front of you, so I started looking around at alternatives for him.
ATI sometimes sells a folding stock kit.
But, they're very proud of it apparently because they're between $200 and $269, and that's not even all that would be needed to do it legally. I didn't mention needing to add to the barrel (or another $200 to sbr the gun). Considering it's a metric barrel thread, that even further limits what's available.
So, I ordered a 12" piece of 3/4" rod. Hollowed it out so it would pass a bullet, and threaded it to 13mm to make the barrel extension to bring it to the legal 16" limit. After putting it in place and lathing the exterior into the diameter that I wanted, pinned and welded it. Of course, it got painted afterwards once the filing was done to make it as pretty as possible.
I had started to make a fake flash hider on it, but ultimately decided to just lathe it down to the same diameter as the rest of the portion beyond the barrel threads.
But, here's a pic of the underside after the welding and painting and such just in case anyone questions whether it was done right or not. It was.
Since he had no intention of spending $200 plus for a knockoff mp40 stock, I bought a demilled Pps-43 folding stock assembly to rob some of the parts to make this.
You're probably scratching your head wondering why, but there's an honest answer for that.
I only used the legs and the butt of it. Naturally, I couldn't use it the way it came. Well, duh!!! Because they're not the same kinds of guns.
The Pps-43 stock folded to the top, and the mp40 folded to the bottom, that meant that I had to grind the rivets out and take the butt off and flip it around the other way and also had to flip the legs too (the left on the right and the right on the left). I had to grind a lot of the locking piece to get the angle the way I wanted it so the butt would be the proper angle too.
Where I had to grind the rivets out, when I put it back together, I used #10-32 bolts. So, I literally had to completely take it apart and redo it entirely to be able to use it. Plus, demilled parts means exactly that too. So, that too should also count towards 922 from any way of looking at it. Plus, there's more parts to the assembly that were made in America too. He also bought a US made follower for it somewhere? So, that's enough parts to make it legal.
Sorry. No pictures of the new screws holding the butt on, but that was the only way to get it to look right on the mp40.
Removing the blocker thing on the receiver that ATI installed for import reasons was simple. But, making the internal portions to fit the shape of the gun was a chore. There's a few videos on youtube showing that step of the process from other people. You essentially drill or dremel the welds off of the blocker and remove the stock blocker things which are covering up the channel inside of there.
Below is a picture of the internal assembly I machined after I painted the exterior of the new assembly after I lathed it out. This is the portion that holds the stock legs to the receiver. There's actually 2 different threads that I used to do that. 1/4-20 through the center to join the two halves together and which tensions it down once it's placed through each side of the receiver to make it a solid piece. And if you haven't noticed, there are 5 different diameters to this part.
After the assembly was together, I put a small 10-32 bolt through the receiver as well to prevent it from folding.
Initially, I had considered doing a folding stock, but opted to just do a fixed, mainly because I think the grip portion is probably cast and I was unsure how much it would handle with the gun being pulled into the shoulder and recoil and stuff, so that's why I chose to just lock it in the open position. Which he said was perfectly fine with him. Either way, he's getting what he wanted and agreed that threading a big hole in the receiver that may crack on a part that will probably be terribly hard to replace if it did was a bad idea.
This pic below is before the legs and the butt was installed, but you can see the locking screw through the rear of the gun that keeps the internal parts from rotating.
I only have 2 more holes to drill and thread when my buddy comes back by so I can adjust the angle of the legs to get the proper height so his cheek lines up with the irons well. I'm fitting it to him specifically since he needs to be able to actually use it the way it was intended. You can see the hole that I already drilled through the leg so all I'll have to do is mark and drill it and thread it to lock the leg onto the assembly.
But, other than that, it's done and I just wanted to show off some of the work I did to convert it into a carbine for him. I enjoyed the project, but there was a lot of reverse engineering and measuring to make the various parts and to make them work. I don't know of anyone else who has went this route, but he paid about $55 for the buttstock and the aluminum rod for the various parts, so that's a heckuva lot better than what the importer is wanting for the stock assemblies. And should make it a lot more fun to shoot.
ATI sometimes sells a folding stock kit.
But, they're very proud of it apparently because they're between $200 and $269, and that's not even all that would be needed to do it legally. I didn't mention needing to add to the barrel (or another $200 to sbr the gun). Considering it's a metric barrel thread, that even further limits what's available.
So, I ordered a 12" piece of 3/4" rod. Hollowed it out so it would pass a bullet, and threaded it to 13mm to make the barrel extension to bring it to the legal 16" limit. After putting it in place and lathing the exterior into the diameter that I wanted, pinned and welded it. Of course, it got painted afterwards once the filing was done to make it as pretty as possible.
I had started to make a fake flash hider on it, but ultimately decided to just lathe it down to the same diameter as the rest of the portion beyond the barrel threads.
But, here's a pic of the underside after the welding and painting and such just in case anyone questions whether it was done right or not. It was.
Since he had no intention of spending $200 plus for a knockoff mp40 stock, I bought a demilled Pps-43 folding stock assembly to rob some of the parts to make this.
You're probably scratching your head wondering why, but there's an honest answer for that.
I only used the legs and the butt of it. Naturally, I couldn't use it the way it came. Well, duh!!! Because they're not the same kinds of guns.
The Pps-43 stock folded to the top, and the mp40 folded to the bottom, that meant that I had to grind the rivets out and take the butt off and flip it around the other way and also had to flip the legs too (the left on the right and the right on the left). I had to grind a lot of the locking piece to get the angle the way I wanted it so the butt would be the proper angle too.
Where I had to grind the rivets out, when I put it back together, I used #10-32 bolts. So, I literally had to completely take it apart and redo it entirely to be able to use it. Plus, demilled parts means exactly that too. So, that too should also count towards 922 from any way of looking at it. Plus, there's more parts to the assembly that were made in America too. He also bought a US made follower for it somewhere? So, that's enough parts to make it legal.
Sorry. No pictures of the new screws holding the butt on, but that was the only way to get it to look right on the mp40.
Removing the blocker thing on the receiver that ATI installed for import reasons was simple. But, making the internal portions to fit the shape of the gun was a chore. There's a few videos on youtube showing that step of the process from other people. You essentially drill or dremel the welds off of the blocker and remove the stock blocker things which are covering up the channel inside of there.
Below is a picture of the internal assembly I machined after I painted the exterior of the new assembly after I lathed it out. This is the portion that holds the stock legs to the receiver. There's actually 2 different threads that I used to do that. 1/4-20 through the center to join the two halves together and which tensions it down once it's placed through each side of the receiver to make it a solid piece. And if you haven't noticed, there are 5 different diameters to this part.
After the assembly was together, I put a small 10-32 bolt through the receiver as well to prevent it from folding.
Initially, I had considered doing a folding stock, but opted to just do a fixed, mainly because I think the grip portion is probably cast and I was unsure how much it would handle with the gun being pulled into the shoulder and recoil and stuff, so that's why I chose to just lock it in the open position. Which he said was perfectly fine with him. Either way, he's getting what he wanted and agreed that threading a big hole in the receiver that may crack on a part that will probably be terribly hard to replace if it did was a bad idea.
This pic below is before the legs and the butt was installed, but you can see the locking screw through the rear of the gun that keeps the internal parts from rotating.
I only have 2 more holes to drill and thread when my buddy comes back by so I can adjust the angle of the legs to get the proper height so his cheek lines up with the irons well. I'm fitting it to him specifically since he needs to be able to actually use it the way it was intended. You can see the hole that I already drilled through the leg so all I'll have to do is mark and drill it and thread it to lock the leg onto the assembly.
But, other than that, it's done and I just wanted to show off some of the work I did to convert it into a carbine for him. I enjoyed the project, but there was a lot of reverse engineering and measuring to make the various parts and to make them work. I don't know of anyone else who has went this route, but he paid about $55 for the buttstock and the aluminum rod for the various parts, so that's a heckuva lot better than what the importer is wanting for the stock assemblies. And should make it a lot more fun to shoot.