Looking for complete pistol that uses Glock Mags.   Barrel range will be 5 to 8.5 inches.   Will shoot with and without suppressor.   I have built 3 SBR AR 15's in 556 and 300 Blackout which was pretty easy.    It just seems everything I have read here there seems to be a lot of tinkering, adjusting, and changing parts sometimes.   I will be 65 tomorrow and would like to shoot this before I turn 66. I don't want to spend time waiting for parts and changing things around and tinkering.    I have an old truck for that.    Sig  MPX is not completely ruled out but I love my ARs.   Any and all advice and wisdom would be deeply appreciated.

My first choice would be my MPX K’s and Copperhead and then my CMMG 300 series Banshee.  The MPX’s are just softer shooting.

I would say a CMMG RDB build is great choice. I have the 5" setup with a Cozad buffer and a flat wire spring. Its recoil impulse is comparable to my PTR 9CT(MP5 Clone).

Plus you can build it how you want, I built mine around $700 but you could easily get to 2 grand if you want all out on it. Mine shoots perfectly right out of the gate, no tinkering. I feel like CMMGs setup is much more reliable and easier to get going compared to a basic AR9.

If you want a complete gun, I may lean towards an MPX K over a Banshee.

JP GMR-15. They work. Heavy, but with the Silent Captured Spring in the buffer tube, they're quiet. And they work.

Have you looked into  Foxtrot Mike.  I just got mine and love it.  I bought lower separately from upper that way I could get the upper I wanted.  Good luck in your search