For those of you who have been wondering about other projects I have in the works, here's a post for you.
I've taken a couple days off of working on the .50, mainly because I'm waiting for some steel to arrive with which I will work on the bipod and buttstock area.
A while back I procured a couple of Suomi m31 parts kits from a friend, one of which was 100% complete and the other was......not. I have enough parts to build two, but one of them is not going to have all the original stuff. I am saving it for later. First, I wanted to build one that would mimic the original M31. For those of you who are unaware of what an M31 is, go here.
I'm not too fond of the aesthetics of these guns, but the parts kits are cheap, and when it comes down to it, it's hard to argue with a 9mm carbine that holds 72 rounds of ammo in a drum. The biggest problem is, the doggone rifle is heavy. However, the parts kits are still available for around 100 dollars, and are fairly easy to machine the working parts for. One setback I've encountered is that it is originally an open-bolt submachine gun, and in order to be legal, none of the original full auto components can be used in their original configurations. This means converting the rifle to closed-bolt operation, which is a pain compared to the open bolt arrangement. I do not exaggerate when I say that a functional sub machine gun could be built in a matter of hours versus a semi-auto taking a handful of days. This is, of course, if you already have all the springs, magazine, bolt, and small parts.
To start, the receiver of this rifle has been cut to BATFE specs, which nowadays means it was torched apart into three different pieces. This pretty much leaves you with a pile of slag and unidentifiable metal scrap. I had to do a lot of research on this rifle in order to get some measurements that I could transfer to a new receiver. The new receiver could not be capable of accepting the original bolt, so after I took a bunch of measurements, I ordered some 4130 tubing that had close to the same outer dimension but a smaller inner dimension. This will allow me to turn the old bolt down on a lathe to fit snugly in the new receiver, but a standard bolt would not fit. The original bolt will also be highly modified so that it no longer works in an open bolt configuration.
I took some measurements and found that the receiver was 1.46" outer diameter and roughly 1.16" inner diameter. Since the magazine well components would have to be salvaged from what remained of the old receiver, I had to come pretty close to that outer dimension for the old mag well parts to fit snugly on the new receiver. There is also a section inside the original receiver that is about .75" inner diameter where the end of the bolt travels, right above the mag well. I was not about to bore out a 12" long piece of solid stock to two different inner dimensions. Luckily, I was able to purchase some 1.5" OD 4130 tubing from Aircraft Spuce and Specialty pretty cheaply. I ordered it with a 1.105" inner diameter, so that a factory bolt would not fit. I also ordered a piece of 1.5" solid round stock that I could machine to fit inside the receiver and weld in place that would take the place of the original .75" inner diameter section. This section includes the lugs that allow the quick-change barrel to be mounted. More on that later.
Here's the original kit and receiver in all it's......uh.....glory.
The new receiver tubing
Some pics of the kit when "assembled"
First, the magazine well
Next, the slot for the bolt/sear/hammer assembly on the bottom
A bad pic of the bottom of the receiver so far. The flash makes it look like it has been cut all the way through. It wasn't, the long slot on the bottom stops a couple inches shy of the mag well.
The ejection port. That funny looking knurled thing below the receiver is the thread-on end cap that holds the main spring in place.
Now, a slot on the top for the rear sight. Originally, the rear sight is what keeps the bolt aligned and keeps it from spinning in the receiver, as there is a flat running along the top of the bolt that meshes with a flat area on the bottom of the rear sight. The rear sight is also to be riveted in place.
Rear sight held in place
Now, once the receiver is trimmed to an overall length of 10.625", I turned the rear-most end down to an overall diameter of 1.46" to match the original receiver.
Next, I set the gear box on the lathe for 20 threads per inch, just like the original receiver has, and began threading. The reason you don't see the rest of the receiver is because it is inside the headstock of the lathe behind the chuck. That is one of the advantages of this newer lathe.
Threads rough cut, just a couple more passes at .001" each to clean them up,
And, the original receiver cap threads on snugly and cleanly.
Here I'm mocking up the receiver in the original wooden buttstock, with the mag well pieces I salvaged from the old receiver in place. A drum mag was used to get the spacing correct. I found out (almost too late) that if you set up the receiver for a stick magazine, the drum won't fit due to it being thicker than the stick mags. While the stick mags give you a healthy 36 rounds of 9mm on tap, what fun is it if you can't have a 72 round drum? So, a drum is used for mockup and tack welding.
Ignore the coat hangers. This is my garage, after all. I have to deal with having a dryer for a temporary workbench, and the significant other has to deal with having gun parts and tools all over the dryer.
Some buzzing and zapping noises later, I had the mag well pieces MIG welded in place. Normally, these are riveted in place on the original receiver, however I see no need in riveting them on to the new receiver. No sense in making more work than is necessary.
That weird thing on the end of the receiver is the quick lock mechanism for the barrel housing. These have a quick release barrel assembly from the factory. I have to slightly modify the way this works so that an original barrel cannot be used on it to stay within the law. Reason why is because the original barrel is only 12 inches long. That constitutes a short-barreled rifle.
I've mentioned before that in order to build some of this stuff, it takes me longer to do it in compliance with inane laws than it would otherwise. This last portion is an example of that. I have to do ____ before I can do _____ because otherwise I've built a/an machinegun/shortbarreled rifle/AOW/noncompliant light fixture/Improvised Explosive Device, etc.
Now, with that said, I do want a short-barreled rifle or two, I do want a AOW weapon, and I do want a machine gun. However, I will be going through the proper NFA channels to do so, and will pay my 200 dollar tax on each of them. It just sucks I have to do a bunch of mental gymnastics and odd preparation to ensure that at no point am I in violation of any silly laws.
Tomorrow I hope to work on the .50 BMG extractor, so it may be a few days before I pick back up on this Suomi, but I plan to have it finished pretty quickly.
More as I build it...............