Took my new RRA 9mm carbine upper and C-Products mags from Rainier Arms out for the first time this morning. I had done my reading and thought I'd be immune to any problems. HA! Stove pipe and jam-o-matic. The RRA (bottom loading) mag block is as low as it can go, the ejector tuned so that it is as high and close to the bolt as possible, and the mags do not appear to be dragging on the bolt. The mags DO lock back consistently on the last round, but just about every other round's empty case fails to make it out of the ejection port, and instead gets wedged above or beside the next round which manages to get partially into the chamber. This happens throughout the entire magazine. The pics below show some of these jams  Dummies and live rounds eject briskly when hand cycled.

For those in the know, if this is typical, will enlarging the bolt catch notch in the mag block so that it can be lowered further solve the issue? I'd be willing to make that kind of modification if it will work. Alternatively, I could just order the Metalform mags from Spikes. I haven't asked, but I doubt Rainier would take the C-Products mags back. They have been used, after all. I kind of hate to lose that $100 investment though.

Any help appreciated, folks! I can tell that this will be a fun carbine once the issues are worked out!

Spent case wedged inside the receiver with live round partially in chamber.


Spent case wedged on top of live round partially in chamber.


Another view of the above before the bolt was pulled back.


The carbine in question.

seriously, I'll buy your UNMODIFIED mags.  I have had no problems with the c-products mags with my RRA integrated magwell lower.

Infantryman: Thanks,  I may take you up on that, but let's see what comes out of this first. If they can be made to work reliably with a minimum of pain, I'd like to explore those options. I'll definitely keep you in in mind though.

I have to ask dumb questions here. I have seen such a thing like this before on other blow-back firearms.

1) What buffer and spring are you using in this gun? These can really affect how fast the bolt flies back and ejects the spent casing. I use a 6-pos stock with a carbine spring and a RRA 9mm buffer.

2) Try some different ammo in the thing. Try several different kinds to be sure. I reload and if I get the load too mild it can do this. Again, a simple blow-back gun is sensitive as the spring tension, bolt mass, buffer mass, and ammo power as all of these have to work together to get things to function properly.

I'm using all RRA parts: buffer spring, hammer and block. I was using my reloads, loaded to factory pressure. This problem does not seem to be unique; I'm convinced that the problem is withe the magazines.

Infantryman, these 5 C-Products magazines are yours if you want them. PM me and we'll work out the details.

I reload too and have learned the hard way to try REAL factory ammo before I discount the ammo as the problem. Often we are more conservative on the reload and it does not have the power that a good true factory load has. (Its good to be conservative at times).

Try some fresh factory ammo in that gun and double check the mag well depth...a big factor. My RRA works great on ProMags....the ones so many put on the bottom of their list as being no good.

Good luck with this....keep at it, the RRA can be a great gun.

New developments. After reading a comment from someone else, I raised the mag block just a hair. No dice. I was trying to determine if the failures happen mainly one one side of the mag. They don't.



Well, I lowered the mag block back to where it was and thought "I'll show you; I've got some American Eagle and S&B 115grn ammo right here!" So, I loaded 4 of the S&B, then 4 of the American Eagle on top of the 15 or so reloads I had left in the magazine. The four American Eagle rounds went off without a hitch, then the S&B rounds went off without a hitch. THEN, the remainder of my reloads went off without a hitch. Strange indeed. More testing needed.

don't sell off those C Products mags so quickly, I'm sure you can get it to work.  I've got some Pro Mags if you want to borrow them to try.  You mentioned you are using a "RRA 9mm buffer spring" are you using their 9mm buffer as well or a standard carbine buffer?

Hey, Chris. I'm just heading out to the range now to do some more testing. I'm using the RRA 9mm block, hammer, buffer, and spring sold as a kit through Brownells. It is definitely a 9mm buffer, but I'll be bringing my regular H Buffer with me today and see what happens.

Have you checked to see if your ejector is anywhere near the slot for it in the bolt?  What your pictures show is EXACTLY what happens when the ejector doesn't hit the base of the empty case.  When that happens, the fresh round pushes the empty off the bolt face and the empty just rattles around inside the upper.

Seriously, check out your ejector's alignment BEFORE you do anything else.  Read this thread for more information and good pictures of how the ejector fits with the bolt.

As stated in the initial post: "The RRA (bottom loading) mag block is as low as it can go, the ejector tuned so that it is as high and close to the bolt as possible, and the mags do not appear to be dragging on the bolt."

I just returned from further testing. Two brands of factory ammo, including Blazer aluminum, as well as my reloads all ran 100%. No stoppages in the 100 rounds fired, using all 5 of my C-Products magazines. The only other tweak made was to the extractor roll pin which seemed to be sticking out of the bottom of the bolt just a hair. Not sure if that had anything to do with the previous problems, but for now, the issues seem to be resolved. I may run it in next weekend's 3-Gun match just for further testing. Interesting indeed.

I was talking about the ejector issues in that thread, not the possibility of anything dragging.  I'm sorry I didn't make that clearer.

I somehow missed the major tweak you did.  You mentioned moving the magazine block vertically, and in the above post you mention messing with the extractor roll pin.  what else did you do?

That's the thing; I don't know! I moved the mag block up a coupe hundredths of an inch but no joy, so I moved back down again as far as it would go; where I had it initially I thought. I punched the extractor pin up and into the bolt a bit and suddenly the thing started running. Either the mag block is ever so slightly in a different position or the slightly protruding extractor pin was interfering with something. 100 rounds is not a good test in my book, so I won't feel out of the woods until I can put several more though it, but I feel much better about it now. I'll keep you updated.

I am having the same isues with a Colt mag block and somr new C product mags

It could be that before you didn't have the block down quite as far as you do now.  I put mine as low as possible-the mag catch stops it going down any farther-and it works great with CProducts magazines.  Having the block that low did not in any way mess up how the carbine operates with the RRA-modified Uzi mags that I got with the carbine, so I think it's a very good compromise.  Plus, this lets me remove the block to clean the powder residue from the inside of the mag well (blowbacks are filthy) and put it back in exactly the same place every time.

The extractor roll pin could indeed have been snagging something as well.  Whatever it was, the magic seems to have worked.  I'm looking forward to hearing more.  Maybe I'll be able to get to the range on Tuesday and put some rounds through my own carbine; it's been WAY too long since I did that.

Which Colt block?  The one-piece?  A two-piece with tension screws?  Do other magazines work?

The Mag Well adjustment has to be  just right on some guns. Its a combination effect. Changing the height a few thousands of an inch or a different magazine can matter. I just got done working on a KelTec pistol that had me cursing KelTec and the guy who sold it to me. A very few simple operations on it and all of a sudden the gun ran perfect on all ammo and under all conditions. Its amazing how  a small thing that isn't just so can mess up an auto loading firearm.

Cross your fingers and keep shooting that RRA. As a general rule the more you shoot it, the better it will work. It appears that you have it dialed in now. Go enjoy!

Two piece with roll pins. No tension screw. I have never had any failures out of the rifle using Colt  mags with any type of ammo.

GHPorter: I had the mag block as low as it would go and bottomed out against the mag catch the first time as well, so I'm inclined to think that it may have been the extractor roll pin protruding slightly at the bottom of the bolt. That said, I also noticed, when I moved the block back down that it can be rocked ever so slightly fore and aft before tightening. so, perhaps the lading edge is either higher or lower than it was initially. I'll be doing some further testing this week in preparation for a match this weekend. Unfortunately, all I've been able to find locally are Berry's 124 grn HP bullets, so I'm a little curious about how they'll feed.

It is amazing, and slightly irritating, that the system can be so delicate that a few thousandths of an inch can be the difference between 100% functionality and 0%, but that does indeed appear to be the case. I've been spoiled with my CZ handguns and my ARs in that I've never had a problem; I'm not used to these type of issues and hope that I can get this carbine to the point that I can count on it 100%. THAT will be enjoyable indeed!

Many guns are sensitive to certain measurements. Some, like AK's are made to tolerate bigger differences. Look at .22 conversions in the AR's, all sorts of issues crop up. We have to remember that the AR was not designed to be a 9mm, or a .22 or anything like that. So, the design was modified for the 9mm. If all AR's were built to be 9mm's then the designers would be careful to optimize the rifle for that round. As is it they had to sort of go at it backwards, forcing the 9mm (or .22) to work in a machine that was never designed for those calibers.

I have owned a few firearms in 40 + years of shooting, its not so unusual to have a hic-up here and there. I am amazed that these AR's we throw together from mixed pars even work! Its a credit to good design and manufacturing of the parts that they work as well as they do.

Enjoy that rifle. Learn about what it likes and what makes it work and go shoot the thing.

Ahh but you need to make allowances for this becuase it's a custom build you have.  If you purchased a factory COLT 9mm it would have run out of the box becuase of the MetalForm magazines, and the block would have been the right height, etc.  If your had a Rock River 9mm out of the box it would have ran becuase they would have supplied a modified UZI mag, test fired, etc.

I have a 9mm lower ready to go just waiting on an upper.  I hope to GOD it runs 100% right out the gate.  Otherwise you'll be reading my post in a few months

That is an excellent point, and one I often overlook.