Sunday, July 22, 2012

A finished, Finnish Suomi M31. From scrap steel to shooting steel.

I've meant to put a few pics of a completed Suomi M31 rifle for a while, and I'm just now getting around to it.
I machined the diameter of the bolt, machined a new firing pin, bored out the fixed firing pin, machined off the bolt feed lips, stretched the barrel, bored the barrel shroud for the barrel, cut the rear receiver threads, and rebuilt the trunnions for this particular rifle, the owner did all the welding and completion machine work on it.
The stock isn't the nicest, but it serves the purpose.
This rifle meets 922R compliance, and out of the following

27 C.F.R. 478.89 lists 20 parts:

(1) Frames, receivers, receiver castings, forgings or stampings (USA)
(2) Barrels (import)
(3) Barrel extensions (USA)
(4) Mounting blocks (trunions) (import)
(5) Muzzle attachments (NA)
(6) Bolts (import)
(7) Bolt carriers (NA)
(8) Operating rods (NA)
(9) Gas pistons (NA)
(10) Trigger housings (import)
(11) Triggers (USA)
(12) Hammers (USA)
(13) Sears (NA)
(14) Disconnectors (USA)
(15) Butt stocks (import)
(16) Pistol grips (NA)
(17) Forearms, hand guards (NA)
(18) Magazine bodies (import)
(19) Followers (import)
(20) Floorplates (import)

We have 8 imported parts, which is less than the maximum of 10.
None of the original full auto parts work in open bolt/full auto operation anymore, nor will full auto parts fit on this rifle. The trigger housing has been permanently modified to prevent conversion to open bolt and now uses a hammer, the receiver diameter is reduced so that an original bolt will not fit, the bolt is slotted to prevent use with a full auto sear, the feed lips on the bolt are machined off, the fixed firing pin is removed and a floating firing pin installed, the receiver nose has a smaller diameter so a short barrel will not fit in the receiver, and the barrel is stretched.

After I did the work that I did, the owner came to my shop and used my tools to finish building the receiver. Once he had done the rest of the welding and machine work, we cleaned up the welds and machine marks, then put all the pieces together. The owner is planning to throw some Duracoat on it and give it a factory-fresh look.
Some sanding marks remain in the area where the two receiver sections were welded together, but the owner says he can get those polished out on his own.

Not bad, since this is what we started with.

Here, the front trunnion, the ejection port, and the receiver nose have been completely rebuilt, while the rear mag trunnion has been rebuilt, but not fully shaped or ground yet.

Here are two new receiver sections, one in place on a rebuilt receiver section, the other being used to support the drum. I machine these a bit long, and allow the end user to trim them to size before welding.

The barrel extension now protrudes from the barrel shroud.

Cleaning up and polishing the welded, ground, and machined areas.

 All together now, ready to be welded into a single piece, then have all the remaining machine work done.

Mocking it up in a stock to make sure the receiver is the correct length.

Here is the rear receiver, with a template glued on to it. The receiver can be welded before being finished machined, or the other way around. As long as everything is aligned beforehand, it is unimportant which you do first.

The same template/receiver, but with the glue releasing the edges a bit. The centerpunch marks all align, and that is what counts.

And here's the rebuilt front trunion with the barrel shroud attached.

Finally, here's the complete rifle.

I kept the removable barrel shroud feature. Turn that lever in front of the drum and the barrel shroud can be twisted and unlocked, allowing it to be removed. The Finns did this so they could swap out barrels with ease.

That's from a 70 dollar parts kit.
There's nothing like doing a mag dump when you have a 72 round drum of 9mm available.

Tuesday, July 17, 2012

Dallas Area Blogshoot II, updated

Well, it looks like we have set some things in stone for the DAB II.
It looks like Bob S. will be hosting dinner at Campo Verde over in Arlington on the evening of the 15th of September. The exact time is still unknown.
I will be hosting the range trip at my gun club south of the metroplex. It looks like we are planning to meet up at the same gas station as before, at the intersection of I-45 and Belt Line, at 0900 on the 16th of September.
There are no range restrictions beyond the usual, no alcohol, no tracers, etc.
If you're interested in attending, but can't make it to the range that early, please get in touch with me so we can arrange to open the gate at the range for you whenever you arrive. You can email me and I'll give you my personal cell number or just tell me what time you can make it.
This looks like it's going to be a great time, both at the restaurant and at the range.
I don't know if we'll have as many guns as we did at DAB I, but I think we'll come close.

I'll have some new stuff for everyone to shoot, some of which is undisclosed.
Come to the DAB II, and sate your curiosity.

FWIW, all attendees will pay for their own meals on Saturday, but there are no fees at the range. Just show up, try to bring some guns and ammo if you can, and have a great time.

This isn't just for us Texans, so if you're from another state and you'll be in the area that weekend, you're all welcome to attend. Just drop me or Bob S. a note on our blogs so we can get a good head count ahead of time.
Family is welcome to attend both the dinner and the shoot. The range is kid friendly and there will be plenty of training firearms there for new shooters young and old.

With that said, back to my normal sporadic blogging......

Thursday, July 12, 2012

Time for some RPD work....

I have been working on Suomis non-stop lately, and I've gotten kind of tired of the monotony of it. It's been nice to make some money on the side, but I'm kinda glad I haven't taken on any new orders as of late. Since I'm a bit worn out on building Suomis, and since today was my birthday, I decided to work on one of my own projects that I haven't touched in a while, the RPD rifle.
Here's a comparison of the
Original rifle
a DSA modified model.
Some background on the RPD........
The RPD was a Russian assault rifle, and was a decent belt fed machinegun in it's own right, IMHO. I have never shot one in full auto, but it was single-man portable, held 100-round belts of ammo that conveniently stored in a small drum, the belt links were non-disintegrating, and it shot a medium range rifle round. What's not to like?
Though the original design of the RPD has it looking quasi-RPK-ish with it's "club foot" buttstock, the bolt design, ammo feed design, and FCG are all it's own. The RPD fires originally from an open bolt, which means we have some serious reworking to do in our future.
As mentioned previously on this blog, since 1986 when the Hughes amendment (spit) was unlawfully passed, the construction of civilian transferable machine guns is outlawed. (The BATFE has ruled long ago that a open bolt FCG automatically construes a machine gun*)
The Treasury Department/BATFE will no longer accept a tax paid on the construction of new machine guns UNLESS they are made by an 07/SOT who is making them for military and/or law enforcement use.
I am not one of those groups, and I'm not an FFL of any kind, so it looks like I will have to build this rifle into a semi-auto.
To do that, I must modify all of the working parts of the rifle that allow it to fire from an open bolt, and ensure that not only will they fire in a semiautomatic manner, but that full auto parts can never function in the firearm. One thing I already did was weld in denial areas on the front of the bolt channel, so that a full auto bolt will never fit in the receiver, then after my bolt is modified to semi auto, I'll grind that much of the bolt rails off the carrier so that it will chamber a round.

Previously, I had began to work on the RPD, with a game plan of making the rifle hammer-fired, instead of the conventional striker-fired systems that are so prevalent with these guns in the aftermarket.
In my opinion, the striker system is less than optimal in these rifles, and I'll do what I have to do in order to prevent using one. I don't want a mushy trigger, long trigger pull, or anything else associated with striker FCG in this old rifle. What do I want? Well, for all intensive purposes, I want an AR trigger, or at the absolute least, an AK trigger.
Since this rifle is of Russian origin (though mine is a Polish-built example), it made sense to integrate a AK trigger group.
The AK trigger group would not come close to fitting in the place of the old trigger/sear spot, so I machined the bottom off of the lower receiver so I would have a flat area to work with when I get around to building the FCG housing. That is coming down the line, first I have to have the receiver built.

Now, there is a recoil spring that is held captive in the buttstock that has a rod attached to it. This rod protrudes through the front of the stock into the receiver, and fits into a divot on the bolt carrier. In normal operation, the bolt carrier is at the full rear position, the trigger is pulled, the sear drops and releases the bolt carrier, which slides forward, strips a round from the belt, and as soon as the round is chambered, the gun fires.
That recoil rod is going to be in the way of a hammer impacting a firing pin.
There are two ways to work around this.
1. Machine a new hammer that is clearance cut to miss the recoil rod and strike a large pad on the rear of the firing pin
or 2. machine a block that attaches to the bolt carrier and has the recoil rod pressing on it, and machine a hole in the middle of the block that allows a normal AK hammer to pass through.

I picked option 2. While it's pretty straightforward, it means that I have to lengthen the receiver just a bit to allow the correct amount of bolt travel with the new bolt extension in place. I figured one inch of extra length will work fine. Since I had already done some reconstruction and welding on the receiver, I picked up where I left off.

So, the first thing I had to do was take some measurements off the inside and outside of the receiver so I could machine some new pieces to fill in the gaps left behind from the drunken monkey that cut the receiver with a torch.

In this picture, you can see how large the gap is between the torched sections. This was about a half-inch gap. Not bad, and though it could have been filled with some scrap metal and some weld, I chose to mill out some new filler pieces.
 Here is a picture of the receiver as it sits, with some re-weld work done already, indicated by the visible heat marks present. (Not shown here is the area inside the receiver where the bolt channel was welded to prevent a full auto bolt from fitting in.)
I'm not a fan of trying to fit new receiver sections in with angled cuts on both ends, so....

A protractor gave me a straight reference point to scribe a straightedge onto.

Here is the new side plate I machined. Some may notice that the insides of the new filler pieces are machined to match the inside of the receiver as well.

After some creative cutting, grinding, welding, more grinding, etc., we now have one side done. Please excuse the mess on the workbench. I tend to spend more time building than I do cleaning, and it often shows in how messy my work area gets.

A closer view of the welded and sanded area. There are some low spots that I will fill in with weld before sanding smooth again.

Here you can see the one inch difference in the bottom channel of the receiver. After I trim about .5" off the length of the lower receiver, this whole remaining slot will be filled with weld so that a full auto lower receiver can not fit on the main receiver..

Here you can see the gap between the top cover and the rear of the receiver. This amounts to exactly one inch that I will have stretched the receiver.
I have yet to finish the other side, but it will be done in a similar manner, with the exception that a relief will be milled for the charging handle. Now, for those of you reading this who are attempting to build an RPD, and you either don't have a complete receiver, or you are building your own, here are the measurements of the side plates, except for overall length.
This is for reference only, or for machining your own reweld jig.

Use this at your own risk. I took these measurements with a Harbor Freight digital caliper and they all worked well on my reweld jig as well as the new filler pieces I machined. Everything lines up perfectly.
When I'm done with this build, I'll likely put up full dimensions of the receiver for those interested.

That's all for now, believe it or not that took about 5 hours to do, from machining the new pieces to welding and sanding.
Now on to the other side, and then back to the Suomis!

This has nothing to do with RPD's. This is the Chloe dog, resting on my bed. She is our initial line of home defense, as mentioned in my previous post. For those of you who have never met our canine friend, she is an absolute sweetheart,** and she is BIG. That is a King size bed she is sprawled across, and yes, her hind legs are almost at one end of the foot of the bed, while her front paws are at the opposite side of the foot of the bed. She is just this side of being a barking horse.

*The BATFE ruled an open bolt is a machine gun, except on guns that they say aren't machineguns.There is a big debate with the BATFE over a number of MAC10 style open bolt pistols that they declared were not machineguns, due to date of manufacture. More of the BATFE's shenanigans, nothing new here, move along.

**Unless you are not welcome in her house.