Semi Auto PPSH-41 SBR Build from a polish parts kit with pictures

[Connor]

Sharing my hammer fired PPSH design here. Been meaning to post this for over a year but it’s taking this long to work out some kinks. Finally, I am ready to post about the lessons learned. 
 

Picked up a polish parts kit from Robert RTG in 22’ as well as a 9mm barrel from apex. The kit was freaking nice, probably unissued. 
 

submitted my form 1 immediately, approval took about 30 days back in spring of 23’. I got started working on the trigger mechanism while I was waiting for the form 1 to be approved. Many guys do the striker fired design, nothing wrong with that, I was just determined to make a hammer fired mechanism work. I read that an sks trigger group will work but never saw a good write up on it. So I bought an “incomplete” sks trigger group for $40 on apex and made it work with the ppsh trigger housing. I didn’t make any mods to the sks trigger at first, wanted to see what would work /fail first so I pinned the sks trigger housing to the ppsh trigger housing. 
 

I then had to machine the lower receiver of the ppsh to make room for the sks hammer and disconnect or to protrude through. I welded an extension to the disconnector so that it engaged with the ppsh bolt, it just needed to be .200 longer and .060 to one side, talk about precise welding. This disconnector is important bc it prevents someone from pulling the trigger while the bolt was out of battery. I welded in a simple blocking bar to the lower, and notched the ppsh trigger housing accordingly and wala I had a semi auto lower. 
 

Now for the fun part: The bolt modifications. I still removed .900” from the back end of the bolt just like a sticker fire design but didn’t reuse the cut off material. I removed the fixed firing pin, turned my own firing pin housing on a lathe that fit the same hole (thru hole was for an ar style firing pin), relocated the recoil spring to the side of the bolt by machining a pocket with a ball end mill that the recoil spring drops into, machined out the base of the bolt with a ramp that would cock the hammer after being fired, started with an AR firing pin but ended up having to modify it slightly, made a firing pin extension out of tool steel for the hammer to strike, and lastly welded in a blocking bar to the upper receiver as well as a respective slot on the bolt for it to ride.
 

Many guys who run 9mm in ppsh mags have nosedive issues as well. The .220” difference is cartridge length is the culprit. I was no exception to those flaws. I have modified my drums with .187” steel spacers that I welded in place but haven’t gotten around to modifying my stick mags yet. The spacers worked good after I dremelled the each spacer into an acceptable feed ramp.
 

No issues welding the receiver back together, it’s straight enough, I see flaws but most guys don’t. I recommend using an aluminum or brass backing plate to minimize cleanup on the inside of the reciever. It’s hard to clean up welds on the inside of the receiver with a grinder, a dremel works but it’s time consuming.
 

fitting the barrel was simple enough. I cut the 1/2-28 threads off the front. I wanted an “original” length barrel to utilize the primitive muzzle brake. If you leave the threads, the barrel sticks past the front of the brake. Didn’t worry too much about recrowning, just lightly sanded the muzzle. You must match drill the barrel to the trunnion. I set the barrel to my desired depth in the trunnion. You could bottom the shoulder of the barrel out on the trunnion, which is probably what you would do with a tok barrel, but I placed my barrel closer to the magazine due to the .220 difference in cartridge length of the 9mm. The barrel was soft enough that a new TiN coated 1/2 drill bit worked great, go slow. 
 

finished off the build with armor black cerakote and she’s looking good.
 

All in: 

$650 parts kit (now they are $500 with a 9mm barrel on Bowmanarms.com)

threaded barrel from Atlantic: $150

sks trigger group from apex: $40

3 drums($80ea): $240

3 stick mags ($50 ea): $150  

Tax stamp to the man: $200

Total: $1430

Honestly this was a big project in my book, I was happy to take it on but I easily have a few hundred hours invested. Nothing cooler than shooting my ppsh though next to some guys at the range that just dumped over a grand into their PCC. The ppsh draws some cool attention for sure. 
 

over 1000 rounds of 147gr AAC through it at this point with many hick ups. Most of my failure to feed issues improved though after I modified the drum feed lips. Running much better now. 

Happy to answer any questions about this build, just had to get this off this off my chest. 
 

cheers, 

Edited May 8 by Connor

[timkel]

Well done!.. Appreciate the detailed description.

[Rekraps]

Very nice. You guys are skilled machinists!

[PMW6769]

How hard was the receiver to weld back together? Also does the barrel just float inside the shroud except for the bottom being attached to the trunion? 

[Rekraps]

I have to say you do some really good work. Best of all though, is the solution for shorter 9mm round for the drum. Brilliant. 

[Connor]

On 9/4/2024 at 6:35 PM, PMW6769 said:

How hard was the receiver to weld back together? Also does the barrel just float inside the shroud except for the bottom being attached to the trunion? 

Receiver was fairly easy to weld back together. The outside of the receiver was very easy to clean up post weld but the inside was much more difficult. I’ll definitely be using a welding jig next time to prevent over penetration on the inside. I used a grinder to clean up the majority of the work and dremel to fine tune the welds on the inside. 
 

the barrel is just floating in the shroud. It’s held in place by the front trunnion, the barrel slightly over laps the start of the primitive muzzle break. 
 

Hope this helps!

[Connor]

On 9/5/2024 at 5:28 AM, Rekraps said:

I have to say you do some really good work. Best of all though, is the solution for shorter 9mm round for the drum. Brilliant. 

Thank you! 

[signal_4]

Great Build !!!! I just got my form 1 back on my 1944 Molot. Got the kit from Appalachian Arms.  My bolt is striker fired. I had Justin Polhamus, JP machine, do the conversions bolt, lower,and FCG and I did the rest. Trigger set is still original. Used a KP products 9mm barrel. 

Edited September 18 by signal_4

[DESTO94]

Very detailed description. Nice build!

[Connor]

On 9/17/2024 at 7:00 PM, signal_4 said:

Great Build !!!! I just got my form 1 back on my 1944 Molot. Got the kit from Appalachian Arms.  My bolt is striker fired. I had Justin Polhamus, JP machine, do the conversions bolt, lower,and FCG and I did the rest. Trigger set is still original. Used a KP products 9mm barrel. 

Awesome build to you as well! Hardly looks like a reweld. There is something to be said about doing the striker fire build. I really like the markings and year of mfg on your receiver. I was lucky enough to have both those areas blown out from torch cuts.