I have been thinking about getting one of these and was wondering if they will work with Cproducts mags and others. The RRA mags are a bit expensive and before I take the plunge I would like to here from some people that run this lower and hear how well they run. I will be using a RRA receiver and bolt group as well..

I bought one right when they first came out and it would not run at all with Cproducts 32 rounders but the metalform mags work great.  You can get them from CDNN for about $30 each and I think it is worth it over the CPs.

Metalform 9mm AR mags

Thank you for your input. I have a Spikes Tactical mag block coming in tomorrow but I am thinking I want to run a dedicated lower instead... Those mag prices are not to bad either..

With a standard lower and magazine block you have lots of options.  Metalform mags should work with everything, but they aren't always available or affordable.  CProducts mags are available and affordable but they are not as consistent as Metalform's mags.  Being able to tweak where the block is gives you the option of using different magazines, and I think that's a positive.  With a dedicated lower, you are locked into using specific magazines, and that's not always an optimum solution.

You make a lot of sense. I will give the Spike's Tactical Mag block a try. If all goes well I will just get/build a lower for it. I have nor read a lot about the Spike's mag block but it seemed like a good choice seeing it takes a few different mags and is adjustable.

I am not the expert some here are but, I do have two 9mm AR's. One is built with a RRA mag block, the other is a CMMG dedicated 9mm lower. They call it the "Mk9".  I looked at RRA and CMMG lowers before buying one. From what I read the RRA is picky about the magazines it likes. I  have heard from several people that the CProducts mags are not well liked by the RRA lower.

I got the CMMG lower and it seems to run with any magazine I have. So far I have a modified Uzi mag that works perfect. Bought just one to see how it was. I have several CProducts magazines and they function just great. I even have some of the dreaded cheap @$$ ProMags and the CMMG works with them too. So, if I were buying or building a 9mm AR I would have to go with the CMMG. Oh, and its almost a $100 less than the RRA!.   My standard AR with a RRA magwell block also runs with these same magazines. I did have to learn to get it adjusted just right but that was a quick learning curve. Currently the mag block is in a Cav Arms "plastic" lower and is a blast to shoot, no drama at all.

Many like the MetalForm magazines and I am sure they are "the best". I have never used them as the CProducts mags haven't  given me one bit of trouble and the CMMG lower (working with the CMMG  ramped bolt) has been wonderful and as a bonus, its the best price around.  I had been an RRA fan, having three of their rifles, but when I went to buy their lower and my dealer saw the price difference between it and the CMMG he was shocked. Don't know how they do it, but RRA is a LOT more money and is magazine picky. Having been down this road before and dropping lots of my hard earned money I would just go with the CMMG and be done with it.

If you would like a 9mm upper setup I know someone with a RRA 9mm upper with bolt and block with a proven track record and low round count. I don't need two of them.

I have a RRA dedicated magwell lower that I SBR'd with a RRA 7.5" barrel. It works fine with CProducts magazines...both old and new and also the RRA modified UZI mags. I seriously doubt that I have the one and only RRA dedicated magwell gun that is capable of using CP's mags??

Well I got the Spikes tactical mag block today and just installing it and cycling ammo through it it feeds just fine. Ejects just fine to with Cproducts mags. The bolt hold open seems to work. The Mags are not drop free though.. This is my first 9mm build so I'm just learning this. Cant wait for the stamp to come in for the suppressor!! That is the last piece to this puzzle. CMMG doesn't sell the lowers alone do they? I will have to go back to there website and look deeper..

CMMG sells their 9mm lowers any way you want them, stripped, with internal parts but no stock, or complete.

I found them!! The prices are right too. Called my dealer to see if he can get me one.. I read they are mil spec so my RRA upper should fit right?

I put my RRA upper on my CMMG lower without issue. CMMG does tell you that their bolt hold open is made for their ramped bolt. If you use a RRA non-ramped bolt they recommend you install the RRA bolt hold open. If I recall RRA started making a special bolt hold open for the 9mm. Think it was $9

Odd thing is, if I recall, I have used my RRA upper...and bolt...with my CMMG lower without issue. BUT, CMMG recommended otherwise. Perhaps there were some of the parts that didn't like to dance together on certain rifles.

Thanks for a lot of good info.
I did some looking around and found Double Diamond makes some nice lowers. You can order them engraved and all. A little pricey but very cool..

you are not.  my RRA dedicated runs cproducts mags as well.  I sbr'd mine with a 10.5 RRA barrel.

From what I can gather, CProducts magazines simply have some dimensional variation, so some mags will work fine, while others will give some people problems.  I had little trouble getting my standard lower with RRA block and CProducts mags; a little experimentation produced a "sweet spot" location for the block that works with every mag I've run through it.  But some people say that they can't get CProducts mags to work in their guns regardless of tweaking.  I respect that because I was one of the first purchasers of CProducts' "this should work in every block, in every gun" magazines, and I've followed their ups and downs.  My first order of 4 magazines simply would not seat, no matter what I did.  Larry replaced them and the new ones worked great.  I have not even upgraded them to the "new" followers because they did not seem to. Need them.

I would simply advise anyone buying any dedicated 9mm lower to try a couple of CProducts mags before they buy a bunch of them because it's possible they might not work.  I would say the same thing for just about any non-Uzi, non-Metalform magazine.

Well I went with ordering a Double Diamond lower. I really like the look. Talking to the rep I should get it in 30-60 days.. In the mean time I will run a spikes tactical block in the registered lower I have. The CProducts mags do not drop free from this block though. I have to pull them out even after I removed the finish. I ordered some Metalform magazines to see how those fit...