Saturday, March 31, 2012

For Hyperprapor....

Remember me saying something about AR15 receivers?

Each of those is a 0% AR15 receiver. No machine work done.
Yes, that's 13 receivers total.

Friday, March 30, 2012

Building a semi auto RPD rifle

This post is about my efforts to work on another project as I digress temporarily from working on the Suomi drum/Hi Point match up. Follow along and see what it takes to build what is essentially a belt-fed AK47!

One of the projects I picked up recently was a Polish RPD parts kit. The good folks at MGS sold me a complete parts kit, minus receiver, and every part was in great shape. I do not think this rifle was ever even fired before being demilled. Instead of being torch cut, it appears that the receiver was cut with a chop saw originally. The front receiver stub that was still attached to the barrel was still usable, and I took advantage of this.
I called Sarco and ordered a demilled receiver and about three weeks later, I got in a big pile of slag-encrusted receiver parts. Apparently, whoever demilled the receiver did so with a torch, and it looks like they had beaten the parts apart with a hammer while they were still hot. I was able to get them straightened out somewhat, but they are far from parallel perfect.

Now, since I was using a demilled receiver, the ATF mandates that the receiver cannot be reassembled in a manner that would allow a full auto bolt or bolt carrier to fit or function in it. To prevent any legal issues on this front, I welded up one inch of the rails under the receiver nose so that a standard bolt carrier would no longer fit. In modifying the bolt and bolt carrier, I milled off one inch of the rails on the front of the bolt carrier. I then milled a slot in the bolt itself, and welded a denial pin in the side of the receiver nose stub. This pin would prevent a full auto bolt from fully closing and allowing a round to be fired. I also milled off the stub that impacts the firing pin as the bolt closes, and I also ground off the ridge that holds the bolt carrier to the full auto sear.  I will not be using the original trigger or sear, and plan on modifying the rifle to accept a AR15 hammer/disconnector. This will be a huge difference over the original open bolt system, and will allow for a much better trigger than is available from the semi auto striker systems that are currently available for this rifle. This also solves part of the 922R issues that arise when building a semi auto rifle out of a imported parts kit.

Here is a short quote of the law, and a list of parts that need to be thought about when building one of these rifles.
(a) No person shall assemble a semiautomatic rifle or any shotgun using more than 10 of the imported parts listed in paragraph (c) of this section if the assembled firearm is prohibited from importation under section 925(d)(3) as not being particularly suitable for or readily adaptable to sporting purposes.

Paragraph (C) defines the following parts as "countable" under the law:
(1) Frames, receivers, receiver castings, forgings or stampings *
(2) Barrels
(3) Barrel extensions
(4) Mounting blocks (trunnions)
(5) Muzzle attachments
(6) Bolts
(7) Bolt carriers
(8) Operating rods
(9) Gas pistons
(10) Trigger housings
(11) Triggers
(12) Hammers
(13) Sears
(14) Disconnectors
(15) Butt stocks
(16) Pistol grips 
(17) Forearms, hand guards
(18) Magazine bodies
(19) Followers
(20) Floor plates

Numbers 3, 18, 19, 20 are non-issues. This rifle is belt fed, so there are no magazines and there is no barrel extension.

I will be either using American parts for the following, or making my own:

1. Muzzle brake, so number 5 is out.
2. Gas piston, so number 9 is out
3. Trigger housing, so number 10 is out.
4. Trigger, so number 11 is out
5. Hammer, so number 12 is out
6. Disconnector, so number 14 is out.
7. Pistol grip, so number 16 is out.

This leaves me with 9 imported parts, which puts me in compliance with the law. I may reuse the original gas piston, which puts me at 10 imported parts, still not a legal problem. As such, the decision to use AR15 fire control parts made the list easier to deal with. It's still a silly law that has nothing to do with reducing crime, and only serves to make it harder for us Americans to import or build otherwise perfectly safe and usable weapons.

There will be another post entirely about the modifications to the rifle and receiver in order to make it function with the original recoil spring assembly and a hammer fire control system, as the recoil rod and spring are right in the middle of where the hammer needs to go. I haven't had time to work on this yet, but already know how it will be done.

In this post, I will outline the work done on the receiver so far, including the welding jig I had to machine to line up all the parts and get them welded with out burning holes in the receiver.

To start, I took some important measurements from the receiver side plates I had, and ordered some copper plate from Speedy Metals. I transferred the negative image of the receiver side plates to the copper plate on the milling machine.
Here's the jig being milled for use.

 This is what the receiver side plates look like after being cleaned up and de-slagged. They aren't complex and should be pretty easy to copy if receivers continue to be hard to find.

Here the top and bottom slots have been milled out, now it's time to mill out the middle slot.

 One thing I must mention is that the slots inside the receiver pieces have slight radius's in the corners, so the square-cut welding jig wouldn't fit quite right. I had to put the receiver pieces in the mill and very carefully mill out the corner radius's so the jig fit very tightly.

Now, for the fun part. The receiver has had denial pins welded in, the lower carrier slots were welded in as a denial method for the carrier, and the receiver can now be made one piece. I took some careful measurements and milled the original receiver nose stub down square, and then took the nose stub off the torch-demilled receiver from Sarco and milled it to length and square. I beveled the edges for welding, then started clamping.

You can't tell from this pic, but I had to modify the welding jig slightly to fit around the denial areas of the receiver nose.

Here is the welded 2/3 receiver with the belt feed mechanism in place. Notice that the last 1/3 of the receiver is not welded together just yet, since several modifications need to be made in order to keep the receiver in full compliance with the law, as well as allow for an AR15 FCG to be used.

Here is part of the welded receiver after being sanded down. You can see the discoloration from welding the inside of the receiver. So far, so good!

Here is evidence of my first mistake in this build. I forgot about the non-reciprocating bolt handle having to travel in this slot in the side. By the time I got to this point, I was very hot and tired having been milling, grinding, and welding on this and other projects. So here I am, welding, and very happy with the progress when I notice I've just welded through my bolt handle slot area. D'OH!
I've since cleaned this up some with a Dremel tool, but it sure was frustrating at the time.


Thursday, March 22, 2012

Project digressions

I've been working so much on the Hi Point drum over the last several weeks that I have gotten slightly burned out on it. I cut out all the parts to make a new mag tower and have it all sitting here, ready to weld up, but just couldn't bring myself to start on it at the moment. I figured that since I've spent so much time and money on it, I needed to just step away from it for a week or two and collect my thoughts on the rest of it. I still have some friction issues to sort out even if the newly angled mag tower solves the nose diving issue, and I need a clear head before I try to solve that issue. So, I dug into my project bin and pulled out some parts for one of the other builds I've wanted to start.
Don't think that I've given up on the drum, I'm just stepping away for a week or so to take a break from the usual "one step forward, two steps back" conundrum that the drum project seems to have. I'll pick up on the drum next week or the week after. All the parts are sitting here, and I want to make sure I give it 100% when I do get to working on it.
Anyway, on to the project.
I have a good gunny friend who was lamenting to me one day how there just isn't a viable option for guys like him who would prefer to have a carbine in .45acp. He picked up a Hi Point carbine in .45 at my recommendation, and although it is a viable option, the low magazine capacity and aesthetics of the rifle just don't suit him. He carried a M4 in Iraq, but hated the 5.56 round. He kept telling me how he would have given ten of those rifles for just one in .45 acp. After listening to his laundry list of complaints, I looked into the market of what is available for shooting .45 out of an AR15. It seems that while there are a handful of companies that now make a dedicated .45 AR, none are affordable and many are very hard to get. For years, Olympic was the only company that made one, and they were very hard to find and expensive when you could find them. The available mags for them were also a disappointment. In the market now, there are some who offer a dedicated lower that uses Grease Gun 30 round surplus magazines in conjunction with a .45 upper, but are still expensive, not to mention the user loses the option of swapping to a different caliber upper receiver. There is also the option of a blowback action versus direct impingement, but I was only able to find one company that has a production level upper that uses the DI gas system, and it was prohibitively expensive.After all my internet digging, I finally started to see where my gunny friend was coming from; there is a heck of a market out there for a .45 carbine that is affordable and readily available. I can't do anything about availability to the general market, but I can sure help this guy out. I figure it's the least I can do in thanking him for his service in the Marines......

To start, I procured a barrel blank from Green Mountain Barrel in with a .45 caliber bore. It was just a 16" length barrel, making it perfect for this project. I then bought a upper receiver forged blank from DSA, and some steel stock from Speedy metals. Some of this project will be outlined in this post, and the rest will be in another post to come.

To start, the upper receiver blank is literally a 0% blank, there is no machine work done to the blank at all. There are forging seams all over the receiver and the blank is oversize due to the forging process and must be machined to size. This is a problem when it comes to machining, as there aren't any good places to reference a flat surface. With no good flat surfaces, it can't be clamped easily to machine the necessary surfaces to size. Once either the top or bottom is perfectly flat, the rest of the receiver can be easily machined. After some head scratching, I finally figured out how to clamp the receiver to start milling it down. I had to extend the width of the jaws on my mill so the take-down lugs could be secured, and since the lugs are not flat, I had to make some shims that would allow me to get the receiver as flat as possible. Setting this up took several hours to get the upper with less than .001" of slope, they are just that deformed when in the raw stage.

To start, the receiver was clamped in place, and very light (.001") passes were made across the top of the receiver until a perfectly flat reference surface was registered.

Next, a dovetail cutter was used to cut the 30 degree/60 degree cuts for the picatinny rail. This was done in light passes (.005" per pass) until it met the measurements I found over at Biggerhammers site. I forgot to take pics of this, but the end result is shown below.

Here I tossed a cheap optic on the rail to check for parallel cuts from one side of the receiver to the other. The optic does not sit level front to back because....

......the receiver needed to be referenced and have the slots cut for optic retaining screws! I did this with a .1875" end mill and spaced the cuts out .1875 between slots, each slot cut to a depth of .12"

The end result is an optic that sets perfectly in line on the receiver. I also had to mill the rear of the receiver flat and file/sand the radius on the rear of the receiver to match the curve on a lower AR receiver. After milling these slots, I flipped the receiver over in the mill vise and milled the take-down lugs and bottom of the receiver to spec. Once that top rail was milled flat, I had a good reference surface for cutting everything else.
 Fits good, looks good.
I took such care to make sure everything was machined right, and the end result is that the upper and lower mesh very well. I can't even fit a .001" feeler gauge between the receivers. If you've inspected most production receivers, you might have noticed some slop between the two. One of the complaints my Marine friend had with the service issued M4s they had was slop in fitment, so I wanted this to be good enough a Devil Dog would be proud to hump some miles with it.

You may notice the odd shape on the rear of the receiver; that is where the forward assist would normally go. I am removing that from the receiver altogether, but needed the flat surface for clamping. It will eventually be milled/filed/sanded flat to match the rest of the receiver.

So, the receiver was good to go on the outside machining, but I had one big problem remaining- there was no hole through the center for a bolt or barrel. I chucked the receiver in the 4 jaw chuck on the lathe and got the nose of the receiver dialed in as close as I could get it to center. Best I could get it was about .001" total runout, which is more than good enough.

Start out with a 12" long aircraft drill, 1/8" diameter, and take small pecks until the whole receiver is bored through, then work up to a 1/2" aircraft drill and finish boring it out.

 Step up to a 3/4" drill and keep drilling. Take light cuts to keep it from going off-center.....
 Then remove the receiver and check the rear for concentric bore, before chucking it back up reversed and boring the rear to 3/4".

Clamp the upper in place on the lower and check for bore concentricity with the lower....

Since I will be boring the main receiver out to 1", I wanted the nose to be bored to .745" so I could press in the barrel. This worked out fine with the drill bit I used to bore the nose.

Here is the bottom side of the receiver after milling and boring.

The rough drilled inside of the receiver. I will eventually drill this to .875 and then get a reamer to ream it out to 1.00" so it's nice and smooth.

Here's the nose after being filed and sanded smooth....

The fallout from all that drilling on the lathe........

Next up was the barrel. I put the barrel between centers and measured runout; there was about .010" of runout from the factory. No problem, I just turned the barrel between centers until it was bore-centric. After that was done and the barrel had less than .001" of runout over the length of the barrel, I chucked up one end in the 3 jaw chuck and started profiling the barrel. Here you can see the area I was turning down to be press fit in the nose of the receiver.

After profiling the rest of the barrel down to a 1.00" outer diameter and turning down the shank to .750" for a tight fit in the receiver nose, I popped the barrel in place for a quick teaser picture....

This has been a lot of work to get to this point, so far I have a couple of days of machine time just in the upper receiver and only a couple hours of work in the barrel. For anyone considering building one of these forged uppers, I hope you like hard work unless you have a CNC machine. They are currently about 28 bucks each and a 100% complete stripped upper receiver goes for about 60 bucks. I don't mind the hard work involved because I wanted it to lock up tight to a standard lower, and truthfully it would've been a small challenge to adapt a pre-machined upper to what I wanted to do with it. If you don't have a mill and a lathe and a lot of time on your hands, just buy a 100% upper and fit a barrel to it.

There's more to this project, in fact a whole lot more. I still have to machine a bolt/ejector/extractor, thread the end of the barrel, machine the barrel retaining nut, and make the forearm, among several other things. There is also the issue of magazines, since standard Thompson and Grease Gun magazines are too wide to work with a standard lower magwell. I'll get to that soon, but for now......

Tuesday, March 13, 2012

More HI Point drum shenanigans

Well, I got the formed feed lips welded on, and I was pretty happy with the way they looked and it sure seemed like they would perform well. Of course, it wouldn't be the Hi Point drum project if it didn't give me a headache somewhere......

I am still having troubles with the rounds nose diving and slamming into the feed ramp. I epoxied some plastic inserts into the drum that helped cut down on friction tremendously, and helped the rounds feed through the drum and into the tower more reliably, but it still isn't allowing for enough spring force to keep the rounds pointed up enough to work reliably. I finally in a fit of frustration broke out the CAD program and got to work on a couple ideas. It didn't take long for me to find a couple areas where I was making some simple mistakes that may be costing me time and money.
In designing this whole drum and mag tower project, I kept thinking that the 9mm cartridge is a solid diameter throughout it's case length, and had I stopped long enough to really investigate, I would've seen that it is not. It actually varies about .01" in diameter over the length of the case. This may not matter in a magazine of 10 rounds with a stiff mag spring, ala the factory Hi Point magazine, but in the case of this drum project, where spring tension is less than optimal even with a fully wound center spring, plastic wear inserts, and a decent mag tower, every little bit of force matters when it comes to getting the bullets to nose up as they travel out of the long mag tower. Since the cases are just slightly tapered, by the time the rounds get up the top of the mag tower, there are new issues.
1. the cases are pointing downward because the .01" taper/per round adds up
2. The original spring force that was sufficient to dump the entire magazine before is not a linear force by the time it reaches the top of the mag tower, i.e. it is not equally distributed across the top face of each round. Instead of a straight upward force, the force is now working at odd angles due to the inherent angle of the mag tower as well as the taper of each additional round. To add to that, the mag tower angles forward, and the taper of each consecutive round is also "forward leaning", creating a real alignment issue once the round gets to the feed lips. For illustrations' sake, here is a drawing I worked out real quick in my CAD program. There are no force vector diagrams or anything like that, but it should be pretty evident where the problem lies.

As you can see in the drawing, the angle of the rounds leaving the drum is fairly flat with respect to the drum, but as the rounds travel up the magazine tower, they begin to tip downwards. The difference over 12 9mm cases is severe enough that it will keep this entire project from working correctly until I fix this error.
Now, with that said, the top of the mag tower is on a 180 degree plane, and the top round is pointing just slightly (~3 degrees) upwards, as it should be (technically I think the rounds point even further up from the factory mags, but 3 degrees is enough to work). The mag tower as pictured here is the same as a factory mag, with a 17 degree angle with respect to the 180 degree plane. The angle of the drum in this picture is roughly the same angle as will be needed in real life for proper performance, and it is pretty evident that the angle of the rounds traveling up the mag tower will probably result in some friction. The rear of the case will be in constant contact with the inside-rear of the mag tower. I may be able to glue in a strip of delrin or PTFE strip .005" thick and maybe that will solve any friction issues.
When I first built the drum mag about 9 months ago, I got it to work somewhat well, and that was when I had a mag tower with about a 20 degree angle in relation to the drum. My most recent attempt had the drum on a 90 degree plane in relation to the gun, and didn't work anywhere near as well. It seems that this drawing is calling for at least a 36 degree angle, and possibly more than that if I really want it to feed well.
I hope to have time over the next few days to bend up a new mag tower; I've gotten pretty adept at building those lately =/

So, the new feed lips looked great, were strong as heck, and had the mag tower been to spec, I might have had more success. Since I was too lazy to map this whole thing out until now, I get to build another mag tower and try again. Keep checking back for updates as I get to them......

Wednesday, March 7, 2012


I haven't had much of a chance to update my blog as of late, work and classes have been hitting me pretty hard and I haven't had time to do a whole lot. I have good and bad news on the Suomi drums I've been working on converting; it seems every time I get something successful done, something else pops up to impede me.

I finally got some progress on the last drum assembly I had, and it seemed like it was going to work okay. It would feed about the last 40 rounds in a row without any trouble, and the remaining rounds were just a matter of lining the inside walls of the drum with delrin or something similar to cut down on friction. Unfortunately, I managed to mangle the outside shape of the drum a small bit. I got it pretty close to it's original shape but the cover didn't want to fit back on as needed, and since I've done so much cutting, welding, testing, and modifications to that drum, the drum winding mechanism quit latching correctly. After trying to fix the issue, I finally gave up on that drum. I just couldn't get anywhere with it, because the winding kept letting loose and smacking me. I don't know how many times I thought the drum had broken my finger for me. Enough was enough, I decided to start from scratch. I ordered a few drums from Centerfire and figured they would be sitting on my doorstep shortly. After a couple days of being impatient, I went to MGS and bought a couple more drums. Those weren't in the best shape, but aside from some rust, they did function just fine and they didn't try to remove any of my digits.
I welded another mag tower onto the new drum (though this time I welded it on center with the drum instead of off-center) and loaded the drum up with 9mm Winchester White Box ammo. I found a couple binds in the feed as the rounds ascended the mag tower, and after a couple of slices with a Dremel tool, removed the binding issues therein. I had not formed any feed lips on the mag tower as of yet, and I was curious as to how well the drum would feed with the mag tower on. I loaded the drum up again and hit the release on the back of the drum. This literally dumped the drum empty in less than 2 seconds, so I know there weren't any friction issues, or at least not enough to hinder a smooth feed in a rapid fire test. My next challenge was to design a new set of feed lips that would allow the rounds to tip up slightly and be fed smoothly into the chamber. This is where I am currently, I have half the lips designed and welded on. It seems that what I may have to do is set it up where the bolt reciprocation actually pulls the rounds backwards just slightly which in turn causes them to point upwards. Nothing else seems to make the cartridges tip up correctly in the same manner as they do in the factory mags. Trying several different magazine angles on the old drum didn't seem to make a whole lot of difference in the long run as far as how it affected the rounds pointing up. By the time I had the rounds pointing up enough to feed right, the mag was angled so far forward that it didn't feed smoothly at all. I've decided to live with the angle that gave the smoothest feed and see how much I can manipulate the angle of the cartridge feed by changing the feed lip arrangement on the mag. This is what I am waiting to do at the moment once I get enough time to work on it. On top of everything else, I've had to put a power steering rack in my car, and that has taken a couple of days to install and then try to realign the front end.

We will see how this goes. My guess would be that it is getting down to brass tacks; once the feed lip issue is solved I should have a working product. The only other issue I can see is friction, and as previously mentioned, some delrin strips on the inside of the drum should solve that. I saw on the Uzitalk thread where several others were setting up drums on their Mac submachine guns that a decent alternative to the delrin strips was the large zip ties normally used in HVAC ducting. Depending on the price of Delrin, I may just try using the zip ties for now to make sure it solves the problem. More on this as I get to it.