So I am starting a 9mm SBR build, efiled last week starting to collect parts.

I've read the Hahn mag blocks appear to be the best.

Hahns website says for Colt/RRA uppers does that mean just mil spec uppers or do I have to run a Colt/RRA upper?

I was planning on running a Mega MKM upper, and a Ballistic Advantage 5.5" barrel.

Will the Hahn mag block not work with this combo? I was thinking about going with the Hahn "dedicated" block not the bottom/top ones.

Thanks.

Buy a dedicated lower it will be cheaper than a HAHN block

Unless you plan on SBRing the lower and want to be able to use that lower with multiple short uppers.

If you SBR or plan on using the lower for other uppers get the RRA bottom loader, I have 2 and they work great. ADCO sells them for 170.00 I beleive.

Running  Hahn dedicated block in a spikes lower. It has run 100% since day one. Also run a Black Creek Precision dedicated lower. IT is more cost effective to go with a dedicated lower than a mag block set up.

I've run a Hahn top loading block with a RRA 16" upper & Metalform mags with no failures for years. One of the reasons I went with the Hahn was their feed ramps, which I think has a lot to do with reliability.

The dedicated lowers are a cleaner look but I prefer the flexibility of the adaptors. When I started I was running both a 5.56 & a 9mm upper on the same lower, the top loading Hahn made for a quick swap and the 9mm RRA buffer ran fine for both. Any upper should work with the Hahn block, I think they specify Colt/RRA so you buy an upper with a bolt that's cut for the SMG type mags that Colt & RRA use instead of the Glock mag pattern.

I'm running Rudy's (Mad Machinist) mag block and it's a work of art! Running flawlessly for me since I made the switch from a dedicated glock lower to a standard lower with colt mags. I'd never go back!!