I have a 7.62X39 AR with an OPS-416 gas piston kit.
It worked with the original DI system ASC 30 round mags. After the kit installation, rounds would jam after a few rounds.  I cut off some of the buffer spring thinking that there was not enough power rod to send the bolt back all the way.  That did not work.
I worked with Osprey Defense and they had me send the upper to them.  They opened the gas port that might give the rod enough power but it did not.  They tried different mags with no success except with a CPD (C-Products) mag but it wasn’t 100%.  I am not so sure Osprey has had a lot of luck with this caliber. They sent my upper back to me at no charge.
Since then, I bought a couple of CPD mags but they are no better than the ASCs.
I tried my upper with three different lowers so it is not the receiver.  Since Osprey worked over my upper, I do not think that is a problem… it just happens that the AR mags made for the 7.62X39 do not like the OPS system.  Osprey did not think carrier tilt would cause the problem and there was no carrier tilt.  I have the same OPS kit on my 5.56X45. It works perfectly.
I am pretty sure the problem is simply the magazine because it works with a stronger spring.  Also the round is shorter than the 5.56. With the extra space in front of the bullet, it might not shift up enough to get into the feed ramp.  If the spring for the 7.62 mag is the same as the 5.56 the 7.62 might need a special spring.
Last thing I did:
I had a brainstorm.  I took an AK mag spring out of an AK mag put it in my ASC mag and it worked perfectly.  One problem is the spring is about 2 inches longer than the AR spring.  It only takes 25 rounds in the 30 round mag.  I am not sure if the AK spring is overpowered.  Maybe that much extra spring would be too much power. (Harmful to the lower receiver?)
The problem is identified but it is a workaround.  The mag case is made for this caliber but is there a specific spring for it?  Is there a real fix?

I know this is not really helpful

But is there really reason to make an AR piston?

It works just fine using DI


I would get rid of the piston system and buy a new buffer spring

I find it nearly impossible to read posts that have no spacing between ideas posted.

I have several 7.62x39mm AR's and I had to open the gas ports to get them to run. The 20" came from DPMS with a .093" gas port and would not cycle at all. I ended up drilling it out incrementally and ended up with a .124" gas port direct impingement rifle gas system. Any larger and other parts of the gas system will cause restricted gas flow so going bigger isn't really an option. It's working so far.

Magazines are the Achilles heal of these rifles. Expect 50% of the magazines that you buy will not work as is. You can return them to C-Products or ASC and hope that 50% of the ones they send you work and do the return thing all over again. Rinse and repeat.

Magazines should work! People tweak the lips, polish flashing from the followers, change springs etc. clean and lube and may or may not fix the problem. I would be happy with 15 or 20 round magazines that are 100% reliable versus 25 or 30 rounders that are not. Once you modify the magazine in any way you void the warranty.

Sometimes I'll load 20 rounds in the larger magazines and they may run fine. Reliability is much more important than capacity.

Topic Moved

I'd put an original buffer spring back in, a 7.62x39 round has a third more energy than 5.56 so it's rare to see one undergassed. Both of my builds seem to run better with heavy 5 oz buffers. I think slowing the action down gives the next round a little more time to pop up in to position. It smooths out the recoil a bit as well.

As for mag springs, seems both an AK and a 7.62x39 AR mag would need the same strength spring, since you're pushing up the same amount & weight of rounds. I'll gladly give up a few rounds of capacity for reliability.

This.....

 

The problem with 7.62x39mm is that it uses the fastest burning rifle powders, with H322 being on the slower side for this round. The powder charges aren't much different than .223 and the larger diameter bore causes a quicker reduction of pressure as the bullet travels the barrel's length.  It also runs with a lower initial chamber pressure than .223, much lower than 5.56.

Any good look at an AK-47 or SKS carbine's gas port and most people are shocked to see how large they are. Both of those rifles have positive ejection because the gas port is gigantic compared to what we normally see in USA made rifles.

Hi,

You made no mention of what kind of jams you were getting.  If the rifle was functioning fine with your magazines before you converted to piston then its not the magazines.  We need to know the kinds of jams to hazard a decent guess about the problem.  Honestly, modifying your magazine when it worked before modifications isn't fixing the real problem.

The CPD Inc. magazine has a full length AK type spring in it and holds 30 rounds of 7.62x39.  The fact the ASC with the AK spring only holds 25 rounds and it's close to the CPD Inc. magazine is telling me that the spring is binding in the body of the magazine creating extra compression masking the real problem in the rifle.  Help us to help you by giving a little more information please.

Best Wishes:

I like the piston system because it keeps the bolt, carrier, and fire control components cleaner.  It just feels crisp to me.  I guess you could say it is a matter of preference.  But, I am a gadget guy.  I put the Osprey OPS-416 in one of my AR-15s (5.56X45) and liked it so much I bought another for my 7.62X39.  Also, I was told the conversions would not allow the FSBs (Front Sight Base) so you would have to change that out for a conventional gas block.  Another thing said by many people an A2 forend would be needed.  Being one for a challenge, I put the kit on my AR with the FSB and free float forend.  No problems.  I can put the 7.62 back to DI any time but getting it to work is what makes it interesting.  I have several other AR types which keep me busy.  The AR is like the old 50's and 60's cars were...;  so many ways to upgrade and customize.  It is a blast making something that really works well by scrounging and doing it yourself.  Babble, babble, babble..

Thanks for the invitation to give you more info.

I have several ideas about what might be the problem.  First, the Osprey tech opened the gas port in the barrel but not the FSB.  If it needs more pressure, that probably needs to be opened as well.  Since there is no advertisement about how to use these, or any other, conversions with the FSB.  Osprey is the only one that will physically allow it.  All others come with a (proprietary) gas block.

Using the standard spring of several different varieties, the jams occur sporadically.  It is usually like this:  The first three to ten rounds go well then a jam.  After that every subsequent round jams.  By jam I mean that the end of the bullet sticks just under the feed ramp.  The cartridge lip at the top of the crimp does not get caught. on the magazine lip.

I cut coils off the buffer spring thinking that maybe the gas pressure wasn't sufficient to push the bolt all the way back so loosening the buffer spring tension might compensate.  3 coils, then 4, then 5, then I quit.  That did not help.  (I cut the coils before sending the upper to Osprey).

I bought two new CPD magazines but that did not help... with or without the cut buffer spring.

I also have an extra power buffer spring that I have not tried yet because it seems logical that a stronger spring would worsen the problem but I will try that.

Last, I thought the problem might have been because I keep my magazines fully loaded.  I felt maybe the spring in my original mags may have weakened but with the CPDs that is not the case.

Let me know if the jam description gives you any ideas.  Thanks.

Sounds like your rounds are nose diving, the front tip of your next round isn't coming up high enough. Usually a mag issue, either a rough spot in the mag may be making your follower stick, or your mag spring may not be strong enough. The gen III CPDs seem to have pretty strong springs.

I'd try an AK mag spring. If you're confident it's nothing to do with the piston setup the only other suggestion I'd have is to dremel out the front of the mags and open up the feed ramps.

Hello,

Thanks for the reply.  First you need to do a series of simple tests.

The first is load and fire a single round feeding it from the magazine several times.  If the bolt locks back consistently you have adequate gas to function the action.  If not you need more gas. Stovepipes or failure to extract or fully extract may be a indication of a weak extractor spring.

The second is to load two rounds in the magazine and fire.  The first round should load and fire and pick up the second round which when it fires should hold the bolt back.  If no jams your feed lips are OK, and your rifle has adequate gas. Porpoised rounds are an indicator of a weak magazine spring or high bolt velocity.  In 7.62x39 nose diving may also indicate high bolt velocity/overgassing. Not picking up a round is an indicator of high bolt velocity or a magazine issue due to internal friction/weak spring.  Check your ramps too, if your barrel only has rifle ramps and not carbine ramps the nose diving issues may be solved by going to carbine ramps which are more tolerant of high bolt velocities.

If high bolt velocities are the issue installing a heavier buffer may be the solution along with replacing your cut down spring.  I would venture to guess this is a gas issue since the rifle functioned fine as a DI rifle, but the tests should narrow down whats causing the issues.

Regards

Excellent info!

I use a T2 buffer in mine, and 20 round ASC mags which seem to feed perfectly since day 1.

I have fixed the problem with the OPS 416 conversion on my AR 7.62X39.  The nose of the bullet would hit the bottom of the receiver just under the feed ramps.  This was with any number of rounds in the 30 round magazine.  I opened the gas port and then used a stronger buffer spring thinking the gas was low with the conversion because the DI worked fine but that was not the problem or solution.  I then loaded an ASC and a CPD 30 round magazine with AK 47 springs.  The longer stronger springs forced the round up into the barrel sufficiently; however, it limited the magazine capacity to 25-28 rounds.  One of the replies to my problem on this forum said that using the AK spring was masking the real problem. I don't necessarily agree because the only problem is that the bullet needs to get up to the barrel insert or the insert needs to come down to the bullet.

After finding posts on the Internet I decided to modify the feed ramps.  Since the nose of the bullet was hitting below the feed ramp on the bottom of the upper receiver, I had to grind down below the feed ramps increasing the ramp angle allowing the bullet to contact the feed at a steeper angle compensating for the nose dive.  Now every round feeds, fires, extracts, ejects and reloads consistently no matter which magazine or how many rounds I load.

I think the shorter length of the round with space in front, as loaded into the mag, coupled with a slightly lower gas pressure causes the bullet to push forward at a lower angle.  The permanent fix will have to be with the barrel manufacturers by modifying the barrel insert with a steeper angle on the feed ramps.  Also, unfortunately, it might be necessary for the receiver manufacturer to modify the bottom of the receiver for this round.  Hopefully that would not be the case because it would affect the industry if a special upper receiver would have to be made for this otherwise standard AR platform.