the pmag gen3, hex mags gen 1, ETS mags fit some perfectly and too tight on others.

the lancer, magpul gen2 (and earlier) and GI mags i use fit ALL of my rifles.  (so these are what i use as mags ready for SHTF).

but i do have a significant number of gen3's, hex mags and ETS mags i want to use for the range.

my question is, what part of the magazine do i dremel or sand to ensure a good fit?

all around?

What part of the mag goes into the magwell?

obviously it's one of the sides of the mag that goes in the magwell ... but i was hoping it was just one side or a single straight line.

when you have scores of mags, you'd like to do just what is necessary.

if not necessary, why thin out all the sides?

i guess you never need to ask questions because you know everything.  good on ya.  if you only have sarcastic questions and don't have an answer, please move on.

If it was me, I would put something like lipstick in my magwell. Insert mag and it will show you the high spots.

thats a good idea!  thank you

Had this problem with an anderson lower. They ended up replacing it for me.

i said the same thing to one of my lower's manufacturers.  they said, if a milspec GI mag fits and drops properly ... then there isn't an issue with the lower.

More than likely tolerance stacking. I had a Spikes lower do that to some Center Ind mags and a PMAG here and there. Ended up selling the lower and have no issues with my Anderson and SAA lower.

I have a JD Machine Tech lower, 2 BCM lowers and a former 80% lower. My JD Machine lower seems to be slightly tighter than the others, as I've had multiple USGI mags that wont insert without force and/or not drop free. Those mags have nothing visually wrong with them either, and they will drop free in all my other lowers, and will work fine in my buddy's Colt LE6920 lower. All PMAGs and Lancers I have will work just fine though.

If a USGI mag doesn't fit in the JD Machine lower, I get my rubber hammer and lightly hit the areas I can feel are causing the friction until it drops free. Works great afterwards.

I know my 10 round PMAGs fit really tight in my RPR at first. They worn in with use and fit fine now.