Better Czech yourself, a 3D printed Vz. 61 Skorpion

I don't know why, but I've wanted a Czech Vz. 61 Skorpion pistol since I first learned about them.  It's a simple blowback action but the way this thing operates is like the Rube Goldberg of pistols with so many interlocking pieces to make the thing work, and I love it.  They are available off the shelf, but they cost more than I cared to spend, and where's the fun in that?  Parts kits with torched receivers are available too, but from what people have said it's a tricky reweld and needs a jig.  Also available, and right up my alley, is the file for a 3D printed receiver.  It uses the little .32 APC cartridge(7.65 Browning for you metric folks), so printing should be more than adequate.

I ordered a parts kit from Recon Ordnance, and the customer service is top notch, I'd recommend them to anyone.  The parts in the kit were brand new.  Not lightly used, not tested and put in storage, new.  It didn't look like the bolt had ever even been cocked, much less fired.  Also, to my surprise, all the parts were already semi-auto parts, I didn't even need to convert them over.  The holster included with the kit was used, but that's no big deal.  It was a bit dirty too, so I washed it with Lexol leather cleaner, and gave it a good coat of Lexol leather conditioner.  As received on the top, after cleaning on the bottom.  It had some writing on it that wasn't legible until I cleaned it.  Mr. Burianek from 1Ć, I have your holster lol.

With a few different receiver files available, I decided on the FreeMen version.  I made some changes to the base file to suit my needs.  It's made to use a pistol brace, which I don't want, so I blocked off and shortened the rear where the brace would attach. 
Basically, the whole rear of the receiver is now solid plastic.  I also had some trouble with the parts not fitting as well as I thought they should.  The mag didn't click in as well as it should, so I moved the mag well forward in relation to the mag catch by .020" and now it slides into place easy and locks in solid.  I moved the whole fire control group back .015" because the bolt catch was binding on the lever coming off the FCG.  The hammer didn't cock as smoothly as I thought it should either so initial charging was a pain with just the two buttons on the sides of the upper.  The hammer looked like it was hitting too far forwards on the sear causing a minor bind, and after much testing I ended up moving the hammer pivot hole back .020" in relation to the trigger, now it charges like butter.  It seemed like the receiver was just a little too short front to back, so I moved the takedown pin forwards .035" and now it seems to fit like a glove.  I wanted to use the original pistol grip, but didn't want to shell out the money for the uncommon M15x1 tap needed to cut threads for this single use, so I added them into the file and they are now printed right in. The "fire" detent for the safety didn't line up where it was supposed to either so the notch on top of the lever was hitting the upper receiver, so I moved the detent pocket down by about 1/8".  There are several other little changes too, but nothing major. I printed it in eSun PLA+, 8 walls, 99% infill, .45mm line width(with a .4 nozzle), .16mm layer height, 220°nozzle/60° bed, and only 70% cooling fan.  These settings have proven to give me fantastic layer adhesion and make very strong parts.  On the parts I've destructively tested with these settings, they break like molded plastic does, I get virtually no layer separation.  Here's the finished product:

I tested it with both PPU and the hotter Geko ammo, and it ran flawlessly(which is great because .32 APC is expensive and both these brands are cheap-ish).  I will say though that it's best to wear a hat when out shooting.  It ejects straight up out the top, and having hot casings raining down on you is...interesting...  I think there is still some room for improvement in the receiver, but I'll wait until it breaks or wears out, and then adjust accordingly.  I plan to reweld the original receiver eventually at some point too, but with this printed receiver up and running and many more irons in the fire at the moment, probably not any time soon.