Monday, October 22, 2012

More on my RPD project, first time to cycle a belt of ammo

I've been remiss in posting about my firearm projects due to working on everyone else's stuff, but I've made some time to work on one of my own toys lately that I tried (in vain) to get ready for the DABII. That would be the RPD, for those of you who read regularly.
I actually had the RPD at DABII, but I just couldn't get the blasted thing to run. There were a few reasons for this, but none of them took much work to correct.

To start off with, I really didn't care one way or the other if this rifle even remotely resembled an RPD by the time I was done, moreover I just wanted something belt fed to play with that fired a cheap cartridge. Since most of the RPD builds I've seen have been somewhat unreliable, and every one of them has used a striker fired design that may or may not work, I figured I would change things up and use a hammer fired design. The striker system for these rifles has just proven to be too finicky, and when you've got a firearm that only runs ammunition that has a 100% chance of having very hard primers (like Wolf ammo), you need a fire control group that can smack the primer hard, every time. Otherwise you wind up with a very heavy club.
I had a lower receiver and FCG from a H&K G3 rifle sitting here, and that seemed like a good donor piece after mocking it up on the RPD receiver.

That looks like it was meant to be there, if you ask me.

I needed to mill out the bottom of the bolt carrier a little more than I already had in order to clear the hammer.

Now, the original recoil spring system consisted of a rat tail spring and push rod that fit inside the butt stock and extended into the receiver of the firearm, pushing the bolt carrier forward under spring tension. This was great, except it would not work with a hammer fired system, since the push rod would be directly in the way of the hammer. As such, I originally tried to work around that by stretching the receiver an inch, and building a push rod extension that was milled out in the center so a hammer could travel through it, but this wound up not working very well. After thinking about it a little while, I figured I would just go with dual recoil rods, one on either side of the hammer.
This would entail machining a small piece of steel to retain the recoil rods, and allow the recoil spring to push against them. This was made from an unknown piece of steel I had laying around.

The end result....

Now, I needed a recoil rod retainer, similar to the buffer tube on an AR15, but longer and smaller in diameter. I found a piece of tubing in the scrap metal pile that the aforementioned recoil rod pusher fit in and reciprocated without binding, then threaded the end of it for a 3/4" plug. This tube was then welded inside the lower receiver section/buttstock section from the RPD at the same angle as the original.
I then welded in some pieces of sheetmetal to connect all the corners and make the end of the rifle come together a bit better
Let's take a look at it and see how it looks assembled....

 I also removed the barrel and cut it down to 14.5", then welded a flash hider/muzzle extension on.
In the above picture, you can see a aluminum handguard that I machined for it. I probably won't cover how I machined it, as I don't think I'll be keeping it. It's too boxy and just doesn't look right on the gun.

After some thought, I figured that while it was a pretty unique looking rifle, I still wanted something else different to it that had not been tried before. I have a soft spot for NFA toys, especially machine guns, and since I couldn't build this into an actual machine gun, I wanted to do the next best thing and build a bump fire stock for it.
For those of you unfamiliar with the concept, google "slide fire stock". You'll see that with one of those stocks on your AK or AR, you can easily emulate full auto fire. Well, what would be cooler than to do a "full auto" 100 round belt dump?
So, I removed the HK pistol grip, and cut it's mount off the HK lower. I then milled a piece of aluminum that bolts to the AR stock, and has a provision to allow a AR15 pistol grip and a aluminum stand off piece of metal that keeps your trigger finger off the trigger until the rifle is pulled forward by your forward hand.

I haven't got any good pictures of the bump fire stock parts, but here's what I do have.

There's a piece of sheetmetal that encases the aluminum and keeps it reciprocating in a straight line, back and forth. It's not the prettiest thing I've ever built, but it works, and after I do some clean up, it should look a bit better.
On the other hand, I'm strongly considering redoing the entire rear half of the rifle anyway. We'll see.

Now, how does it look in action?

The first round got caught between the bolt carrier and the receiver instead of ejecting, but other than that, it ran great. Prior to this video, I had loaded about 25 rounds into a belt, and shot it off using the bump fire stock. It made for a REALLY good burst, but my cameraman didn't have the camera working, unknown to me. =( It makes for a fun range toy, like many of my other home built guns. It didn't run well at DABII, because there were issues with the feed tray that I could not easily detect, but after getting it home and seeing friction marks from steel case ammo rubbing on the tray and continually jamming the works up, I was able to mill out the offending sections and get a reliably feeding rifle out of it. Next up is to build a better looking handguard and maybe redo the buttstock area. If nothing else, I'll load up a couple belts, take it to the range on occasion, and let 'er rip! a


  1. Yep. It exactly needs another handguard. May be something like magpul AFG.
    Is this bump-fire part of the stock also selfmade?

    1. Hyperprapor,
      Yeah, I really want a hand guard like the M60 has. Anything but that boxy thing I made.

      Yes, the stock is home made. There are no slide fire stocks on the market for the RPD. If you want one you have to make your own :(

    2. Hmm, that handguard will be nice, for sure.
      Well, i thought that there was some aftermarket stock for AR, may be, plus some kind of adapter. Well, it looks even better with one made especially for it.

    3. There are plenty of bump fire stocks for the AR, but none will work with my application. The distance from stock to grip is too long.

      It will look much better with a new hand guard on. Either way, it shoots and is lots of fun. :)

    4. There is a company that sells, ak buffer tube adapter that allow you to screw it on to the back of the reciever in place of the stock, the attached an ar15 buffer tube and the slide fire stock