7.62x25 AR15 Completed! See Pictures Inside!

[Corvus]

OK guys, here is the third and final installment of my AR pistol-caliber project.

The first project, a 9mm Oly system with mid-magwell STEN mags, was a sucessful experiment that guaranteed that the more important .45 ACP project, which can be viewed HERE, would work.

This final project was the most difficult of the three to do. It is a Colt-style system 7.62x25 AR using PPS43 mags. Here is a pic of a PPS43 mag, for those of you who may not have seen one:



The PPS43 mags are ideal for use in the AR15. They are about the same width as an UZI or Colt 9mm AR mag, so they fit right into the magwell with no problems. This is not the case with the other two commonly available 7.62x25 mags, the PPSh41 and the CZ24/26. Both these would require magwell modifications in order to fit. The PPS43 mags are cheap, reliable, well-made, and plentiful. They can be had for less than $15 each when bought in larger numbers from these guys at Allegheny Arsenal

The upper I used was an RRA 9mm upper that I sent to Marty ter Weeme at Teppo Jutsu. Marty installed, headspaced, and tested a 7.62x25 barrel for me. He is a great guy and does awesome work for a very reasonable price. His website is HERE. The lower is a pre-ban Oly Arms lower.

The biggest issue with this 7.62x25 project was the mag block. I chose the ASA block for several reasons: it is one-piece and drops right into the lower receiver without any need for set screws or other means of attachment that might lower the value of a pre-ban lower reciever (I indeed hope that when we wake up on September 14, 2004, all that pre-ban-post-ban stuff is a non-issue), replacements were available in case I ruined mine, and I was able to buy one for about $75. For those of you who don't have as much access to a machinist as I do, you may want to consider the Hahn block. It is also the one-piece as well, but comes apart for easier milling access. Here are a few pics of the ASA block: one from their website, and the others from different angles.









The first thing I did was to plug the original feed ramp "post hole," as the hole was going to be moved forward on the block.



The next thing was to modify the block to fit the wider (front-to-back) PPS43 mags. This was done with a long endmill. You can see the larger opening in this picture:



Notice also in the above picture the brass screws holding the plug that went into the original "post hole." You can see a little open spot where the plug did not get all the way down into the original hole. This open spot has not been an issue, though I may fill it with something eventually.

There are several "ribs" on the back of the PPS43 mag. One runs the length of the mag, and the other two come out of that one long rib. Since federal law requires that the magazines still have to work in the gun they were originally designed for, I could not touch these ribs on the mags. Instead, I had the mag block modified to fit the ribs. You can see the notches to fit the ribs in these pictures here:



The first notch was the smaller one that goes the entire back length of the block. That was started with a broach and completed with a file, once the broach cut enough of a trough. This notch was cut just barely deep enough to slightly break into the holes that are for the roll pins that hold the ejector. So far, the fact that we broke through a bit has not been a problem.

The second notch was the bigger triangular-shaped one cut to accomodate the largest rib on the back of the PPS43 mag. This was done using some sort of large chamfer-shaped mill--I don't remember the exact name--that opened the notch just far up inside the block enough to allow clearance of the notch. Here is a closer look at that notch:



Once the notches were cut, we had to clear out the front of the magwell area of the block in a slight raduis to follow the curve of the PPS43 mags. My machinist figured out the proper degree to mill out, and made a jig that held the block and rotated on an axis at that proper degree, and did the final radius milling. I finished the final fitting with a file. Here is a diagram of the radius degree to mill:



After all that, we re-located the feed ramp "post hole" to the proper place (.25" from the inside front suface of the block). Because a significant amount of this "post hole" area had been milled away to make room for the PPS43 mag, the original feed ramp "post" was too wide to fit in the remaining area. So, we took down the "post" to .25" for the part of the post that goes down into the hole, and milled a .25" hole for the newly-turned post. Then we drilled a new roll pin retaining hole through the new post (we had plugged the original holes in the feed ramp post). You can see a pic of the original feed ramp "post hole" retaining hole and the new hole in this pic:



Since the entire feed ramp was moved forward, the front of the ramp bumped up against the back end of the barrel (chamber). So, a little work with a Demel tool took that down to where the rifle closed properly. Also, the very top of the feed ramp was contacting the bolt and causing it to stay ever so slightly out of battery, so I took that down just a bit with the Dremel as well.

All that remained was to notch the mags. This proved to be the toughest part to do. I only have three mags notched right now, as I need to do a little more thinking on this part. I'd really like to get just a little square notch like on the Colt 9mm mags, as opposed to the larger, rounded-on-one-end notches like on my other two projects. The larger notch seems to work fine with the two-piece mag block setup, but with this one-piece setup, things are a bit more finicky. Two of the mags I have notched feed just fine. The other one was notched too high, and therefore sits too low in the magwell for the bolt to strip rounds reliably each time. As far as an AR mag is concerned, that mag is now scrap, unless I can weld up the entire notch hole and start again. If the cost of research is just one PPS 43 mag (which is cheap and replaceable, unlike the irreplaceable .45ACP Madsen mags), I'm willing to take it. Anyway, the notching of the rest of my mags is going to take a little more time and thought to get it just right. In the meantime, here is a pic of one of the reliable notched PPS43 mags:



And here is the completed gun, ready to fire (after I replace the hammer with a 9mm one):



I've not fired this gun yet, but the properly notched mags do feed correctly, so it will probably fire without a problem. When I test-fire it, I'll post a follow-up.

I plan on sending all the info on this 7.62x25 setup to the folks at ASA, who seemed genuinely interested in whether or not it would work. There is a decent amount of interest in an AR in this caliber out there, and if some company can make a block that works (and perhaps is not as labor-intensive as mine turned out to be), then 7.62x25 might become another regular AR15 caliber option. I hope so. It's a hell of a round.

(As always, feel free to post or e-mail questions. I'll do what I can to answer them clearly.)

[pug]

Corvus that is an excellent conversion and I hope it functions flawlessly for you. In my opinion I think .308 was the best choice because of the different bullet styles and weights available. With reloadable brass available now and a choice in bullet weight/powder burn rate you should have good control over velocity and recoil pulse. You and your machinist deserve a lot of credit.

[Corvus]

[DaBunny]

Corvus, there is no doubt about your creative genius. I am honestly in awe of your creations.

[OddDuck]

[Corvus]

[DaBunny]

slap!:/me slaps $$1 upside the head

[Charlie-2-6]

Nice work Corvus. I take my hat off.
And please add some info on how it shoots, after you've taken it to the range.

[Corvus]

[brass]

[Belial]

Corvus....Hats for for sure and your builds are very cool....

Might I ask why this round in paticular??? I totally understand the 9mm, 45mm, but just kinda wondering about this one. Curiosity has got the best of me...

Cheers

Belial

[brass]

Edit:

Basically a Very High velocity round with small diameter (1400fps .30 cal).


Here is some info on it:

http://www.gunandgame.com/foru.....17008.html

[Corvus]

Brass linked to some good info on it.

I'd add that the ammo is dirt cheap and plentiful. It's a very high-performance round with a long reliable history in Eastern Europe. Fun to shoot, and if I ever get a chance to put it on a registered F/A lower, it would be a blast to shoot F/A.

Also, another reason I made an AR in this caliber is because no one has before. Sort of a virgin thing...

[Belial]

Right on....I am all about getting to shoot more for less whenever possible...

Cheers....

Belial

[Corvus]

OK, here's the latest update on "My Little Bitch." I installed a new feed ramp that has a steeper angle. With the new feedramp, one modified magazine fed somewhat well, and the other still didn't feed. I figured out that the new ramp was now putting the rounds too high. So, I took a Dremel and ground two troughs for the double-feed mag's rounds to feed up into the chamber at the proper angle. Now the one mag feeds both sides perfectly. I may take the angle down on the troughs a bit more: we shall see how it performs at the range. The notch in the properly-feeding magazine is just a bit lower than the one that doesn't work, which means the properly-feeding mag sits higher up into the magwell. Therefore, the angle the rounds travel is less steep on that mag. Makes me a bit concerned that the difference between a good feed and a jam is so small--just a few thousandths. Any ideas on how to give myself a little more wiggle room? I'm loathe to take too much more off the angel of the new ramp: I might take too much off and end up right where I started!

Wasn't able to take it to the range today, due to all the rain from Ivan. Flooding all around the area, and a record rainfall level. Will test-fire ASAP.

Here's a pic of the block with the new feedramp installed:

[Two Dogs]

I have a CZ52 pistol (C&R) in this caliber. It's a very stout round for a pistol. Lotsa boom and a nice fireball at the muzzle. I see that there is foreign mil-surp ammo available at very reasonable prices right now. Stock up, it won't last forever......

[Corvus]

Well, all things are finally working on this setup. After all the time and thought I put in on it, I figured I'd share a few points for those interested in putting together their own 7.62x25 setup. (I may add more later as things occur to me.)

1) Magazine choice. There are three magazines that I know of that are available as originally accepting the 7.62x25 round: PPSh41, PPS43, and CZ24. I chose the PPS43 because it was the only one that fits an AR magwell without needing to modify the magwell, and I used a pre-ban lower. Now that the AWB is gone, others might want to consider the other mags available. The biggest challenges I faced with the PPS43 mags were A) the curved mag fitting into the mag block, B) the ridges on the back of the mag fitting into the magblock, and C) the narrower space between the feedlips clearing the bolt. Out of more than two dozen PPS43 mags, I think three or four did not require me to take a file and file down a bit off the inside of the right feed lip. The bolt would slam into this part of the mag, and once I filed some off, the bolt cleared nicely and the mag still fed perfectly. Fortunately this was a simple process, and did not modify in the mags in such a way as to prohibit their use in the original PPS43 guns.

I think with the use of the CZ24 mags, the user would not have any of those problems, since the CZ mags are straight, have no ridges, and have a wider space between the feedlips for bolt clearance. The challenge with the CZ mag would be milling out the lower and manufacturing mag blocks to fit the wedge-shaped mags. If someone tried to use the PPSh41 mags, they would be faced with the same curved magazine issues of the PPS43 mag, but other issues would be ameliorated, especially the feeding issues that so pestered me until I figured out just how to angle the feedramp and just where to notch the mags (I have threee junk PPS43 mags if anyone needs some!). The new issues brought up by the PPSh41 would be that PPSh41 mags are single-feed, which brings me to my next point:

2) Colt system vs Olympic system. After doing all three of these pistol-caliber projects--two being Oly system, and one being Colt, I am convinced that Oly is the superior system. Why? In a word: FEEDING. The forcing cone that the Oly system uses feeds anything. I know that the feeding issues that I had with this 7.62x25 setup would have been nonexistent if I had been able to use an Oly system. Yes, I know there have been some complaints about ejectors breaking with the Oly system, but with the new super-strong ejectors Oly makes, that seems now to be as big an issue as Colt system ejectors breaking, which does happen on occasion. The 7.62x25 round is LONG, and the Oly system would provide the extra room needed for the round to get into the chamber. THe PPSh41 mag is the only one that would work in the single-feed Oly system. Double-feed bolts can work with single-feed mags, but single-feed bolts won't work with double-feed mags. PPSh41/Oly system would also eliminate the most daunting issue I had to deal with, the very specific angle of the feedramp, which brings me to that point:

3) Feedramp angle.This issue I found to be by far the most important of them all. I don't know the exact angle I ended up with, but it was more than the angle of the original ASA feedramp, and more than the angle on Colt feedramps as well. The ramp I ended up with was one that a fellow AR fan sent to me from his pile of stuff. He had brazed a Colt ramp up when he put together a Colt-style 9mm STEN system, I think. Whereas the original ramp angle was too low, the ramp that he sent me was a bit too high. Ten minutes with the Dremel took care of that, with two nice feed troughs for rounds stripping off either side of the mag as a fringe benefit. Feeding with the one prototype mag was perfect. So, I had my proper mag and proper feed angle, which brings me to my last point:

4) Notch placement. This was almost as important as feed angle, though I suspect that we might actually have had as much as a thirty-second of an inch margin of error to work within. We used the one protptype mag as a "measuring stick" and made a jig off that mag to notch a few mags. They all caught the bolt. So, I had the machnist adjust the jig to notch the mags ten thousandths of an inch closer to the lips. The result was mags that fed just as reliably, and a few cleared the bolt right away. The others needed less filing as the first few as well. I think the notching in this project was much more important than with my first two projects. With those two, I had just used a scribe to notch each magazine in the right place and handed it to my machinist for notching. Each mag fed perfectly. This most recent project--due to the different fit of the magazine, the different system, and the curved PPS43 mag--turned the earlier "scirbe-as-you-go" approach into "scrap-as-you-go," the results of which were three mags that are useless for my 7.62x25 setup. Anyone own a PPS43 that they want to trade three mags for these? The notch on the side doesn't affect reliability at all!

Anyway, after all the time, headache, and work, I got this one working as well. I think I can honestly say that after eight years in the making, all my pistol caliber AR projects are DONE! Thanks again to all of you who helped with your comments, suggestions, and donations!

[Black_Heart]

Sweet!!!! Nice work! You now have a prototype and you are ready for full production! You have more time and patients than I have, that's for sure!

Semper Fi