These are metal, not polymer?
What gun are you using that they tight in?

I never used one in a milled receiver. The only gun I ever had issues with using my Circle 10 waffles was in a WASR, but that thing had a jacked up mag well.
I am always hesitant to file down a mag because it may cause it to not work well in other guns.

Both Firing Line and Arsenal are top quality and the chances of them having out of spec mag wells are practically nonexistent, but at the same time I have never heard of an out of spec Circle 10 waffle mag either.
Difficult to say where the problem is.

I use Bulgy waffle mags from 10 years ago effortlessly in my Firing Line Krink, & my 2 milled Mak 90's. Never had to adjust anything. I've only seen this with Wasr's, & even then the same mag would fit some Wasr's, & not others. I've even had customers come into the store with some Tapco mags, & say they want a Wasr that will take their mags without modifying anything. Wasr # 1, no fit. I grab another new Wasr from the back, & again no fit. Grab a 3rd Wasr from the back, & all his Tapco mags fit perfectly. Now that's customer service. Try that with an on line vendor. LOL. GARY N4KVE