I am currently using a Colt pattern lower (QC10) and yes, the 32+ rnds are a pain to reload quickly, even with the magwell funnel. I think it may be costing me the difference between being a B to an M.
I just ordered a 20 rnd mag and hopefully that will help. So far, I have had zero problems with the Metalform mags. Other that if they hit the ground at the right angle they will puke up rnds.
I am on my third iteration of this PCC and it all started out as being a range toy.
If I get to shoot more, I may try the Glock pattern lower or maybe just a MPX....who knows