Anyone here have experience in converting to 9mm ? Which upper ? Did it run ok ?
Charlie

I assume that you mean for an AR?

Or Tavor.

Or, springfield armory XD?

You mean for colt/uzi style mags? Olympic Arms mags? Sten mags? Glock mags? One using various mag blocks? They all exist.

Yes, for the AR.

CMMG - have experience with three conversions in two dedicated pistols and one rifle.

Pistol runs well, the rifle runs well unless you get some anemic ammo. Pistol is PSA 9mm lower and Glock magazines. You have to remove the lower stock ejector for the CMMG kit. Rifle a standard lower with the CMMG magazine conversion kit in PMAGs.

The radial delay does “seem” to slow down the recoil. Both are good light recoiling firearms to plink with.

This is the route I'd go, except I'd buy/build a dedicated CMMG gun, or two.

I'm guessing you already have a regular lower. If that's the case, I would suggest getting a couple of Mean Arms 9mm magpul mag inserts so you wouldn't have to purchase either a dedicated lower or interchangeable mag block.

I would still suggest using a heavier (9mm--6 oz or heavier) buffer when you're using the 9mm upper of your choice.

I have a PSA 9mm bolt and barrel and have shot the dickens out of it. I built my own upper but their bolt and barrel and whatever stripped upper receiver is about all you'd probably have to get. While you can mix/match various manufacturers bolts/barrels I generally suggest that you use the same for at least the bolt/barrel if you don't outright buy a completed upper.

That would be the easiest cheapest and most straightforward that you could easily swap out with your other regular lowers.

my olympic arms upper works well with the standard AR 223 lower using Sten mags with the adapter---I have an extra upper and adapter for sale

Never saw any reason for a 9mm on an AR.

I have a Foxtrot Mike setup. I originally just bought the upper, and tried magazine conversions (I don't remember the brand) with Gen 2 Magpul 5.56 magazines, but it didn't run at all.

I bought a dedicated FM lower that takes Glock mags, and it runs like a champ, now. Both the upper and lower are billet receivers, and the build quality is great. The last shot bolt hold-open feature works as it should with Glock and aftermarket magazines from Magpul and Amend2. It's a bunch of fun to shoot with a YHM R9 suppressor!

I like the dedicated Aero EPC receivers/parts. Had mine in 8.3" pistol format with a Ballistic Advantage barrel, very uber. Now I've gone 16" Faxon pencil barrel with it but haven't shot it. Why 9mm? Why the hell not. Fun as heck. Using a Toolcraft BCG without problem. Compact lightweight plinkomatic. I wouldn't mess with the conversation parts. Handy, a Glock, an EPC, and some mags that go in either. What a blast...

I have two built on SBR lowers, one with a 10.5" barrel and the other with an 8" barrel...they are a lot of fun, easy to shoot for the kids, and still formidable with +P+ Ranger 127's. Both of mine use standard Colt pattern AR mags, but if I could do it over, I would have built one using a dedicated Glock pattern 9mm mag lower (mainly because I also shoot a G34 and carry a G19).

I'm with DanInAlaska on the Foxtrot Mike setup. It is cheaper to buy a FM lower than a lower and a mag block and the FM just works.

Doesn't matter if it is a pistol or rifle setup, it works.