Sooo, I got a new lower a while back.  It is a CC AR-9 (glock mag) lower.  when I first got it, i put it together, tried a couple of mags (empty), and then had it engraved (and sent off the F1 paperwork).  well today i was messing around with some other mags to see what hi cap mags would drop free from it.  i found out that loaded 40 sw mags either stick really bad on seating them or won't even seat all the way. most empty mags are fine. glock factory and ETS drop free if empty. SMG will do not and KCI (surprise) won't even seat.   9mm mags seem to do better though

i am thinking i am going to need to slightly widen the magwel to fix this.  how easy/hard and how much do you think it would cost to fix this?  who other than the original OEM can fix it?

ETA: Link to lower in question.  CC and joe bob's AR9 lowers are all made by new frontier

ya I was hoping to find someone with a mill or cnc machine that could do it

Yup, length of a magwell is typically too long for an end mill.  As such, as PursuitSS said, broach or EDM.  EDM will be a small fortune.  Broach will be more affordable.  File and your time is cheap, or send the POS back and have them make it right.

ya I am going to call them on Monday.  don't know if it makes it easier or harder but it is a glock mag instead of ar mag.

If you have a local community college with a Precision Machining program, they might be willing to do it for you for fairly cheap, as practice for students. That said, it'll be practice for students, sooooo...