9mm AR?

[Dolomite_supafly]

All you need to do is round the rear that rides on the hammer. The part under the firing pin at the rear. It moves the point of contact on the hammer much higher and that reduces the stress on the hammer and lower. I did it in response to a blowback 7.62x25 upper snapping hammer pins every 100 rounds or so. After the ramp job I never broke another hammer pin so I know it works.

[Johnny Rotten]

Yep that's it
 
Hahn makes both a bottom loading (probably what you want) and a top loading mag block.  The top loader is considered more a permament setup b/c while they both work the AR's BHO catch, the top loader requires you to install the catch AFTER the block has been inserted.  The top loader is considered more dependable since it can't fall out under any circumstance outside a castrophe.
 
I have used both and never had an issue with a bottom loader.. given you're probably going to want to remove the block and then shoot your 5.56 back and forth, it's probably a better option. It secures with set tension screws from the inside.. nothing permament with either block though.
 
The BHO option works on both Hanhs as long as you have a Colt style mag.  The Uzi mags reguire milling a mag catch slot but will work fine but as Dolomite discussed, they will NOT operate the BHO mechanism b/c of their follower shape/size.
 
I have both 25rnd and 32rd Uzi mags.  Every now and then you can catch them for $9-$10 surplus ... the Colt mags are high and certain years demand a premium ... not sure the significance...  Cproduct mags work well too as others have suggested and are the colt pattern.
 
Your factory bolt catch will work with the Hahns.
 
This VM Hytech uses factory Uzi mags but adds a secondary mag release at the bottom.  Good in the mags don't have to be modified but there is no BHO and the secondary mag release give some the weebeegeebees.. .me, I only shoot my 9 when I'm out having fun so I've never had a problem getting too trained on the other.  But I do see pros and cons with each setup.
 
The CMMG Mk9 lower is a completely dedicated 9mm lower that uses colt pattern mags.  There is no block it's machined into the lower and is ONLY a 9mm lower.. I like the dedicated lowers and hadn't seen those quarter 10s .. they look damn good and would be my choice if I was building a dedicated setup.  Beautifully machined no doubt.

Thanks for taking the time to write this out, its helping me decide how to get rid of all the 9mm I have stashed from my m11 days..

[Tncobra]

I bought the oylimpic upper with the sten mag conversion some years back. My favorite rifle.

[Smith]

Oooh! Got it built! Had to tweak the mag lips on the ACS mags. The right side of the mag lips were too tall and the rim extended too far into the mag body for my setup. After filing them down, they all worked great. Looking at the Metalform mags, I don't think they would have that issue on this build.  Ran a bunch of rounds through it today and all I can say is WOW! What a fun gun. Picked up a See All sight and it works great for this gun. I had used one in the past on a shotgun and liked the idea, and for this gun it was a great fit. I could do without the banner on the side, but it's a small issue.

 

[I am Groot!]

Looks great. I like the look of the Colt mags better than the Glock.

[R1100R]

Very nice Nate. I am looking at a 9mm AR real hard right now. :)

[Smith]

Very nice Nate. I am looking at a 9mm AR real hard right now. :)

Wayne, just let me know if you want to take it out and run some rounds through it. You'll end up with one.