Thing of building one up, but can't decide on magazine.
I have a number of UZI magazines I can send out for slot milling, but Glock magazines are more plentiful.

Which one and why?

I had a Hahn adapter AR9 using Colt Mags....2 yrs ago I upgraded to a dedicated QC10 AR9 pistol for/Glock mags. It consolidates mag types I have and seems to function better.  My sidearm is a Glock 19

This has been discussed 100's of times.

The only difference is....

one goes in straight....one goes in at an angle.

You need to decide if you want metal, or plastic mags, and what brand of mag you want to use.

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Having both and being a USPSA PCC Competitor I'll say this:

If you're building a plinker/tactical/tacticool - Use Colt mags. Proven design, super robust mags, less feeding issues due to feed ramp design AND double-feed presents rounds faster.

If you're building a go-fast rig - Use Glock mags. Understand mags are consumables. They're easier to reload on the clock and all the development is for them (extensions, etc).

Also Glock mag builds look like crap

That is why I went with the colt QC10 Lower.

Attached File

I have one of each, both SBR’s. Colt for the win.  My Glock mag lower is a Spikes and the LRBHO is anything but reliable. Also, Glock mag lowers are fugly.

I went with a dedicated Colt lower (PSA).  I think they look better.  I like the metal (Metalform) mags.  I have 10, 20 and 32 round mags.  The feed ramp on the Colt lower is a plus.  The mag release and the LRBHO are simpler on the Colt lower.

In either case you need a good, sturdy mag well vice block.