how the heck did you get it to latch? did you end up filing down the magazine hook for the mag latch? Or file down the top of the feed lips a hair? I tried 3 different arc mags 10-11 months ago when I got my first impact, tried it in a post-2014 ax, KRG whiskey, and finally the foundation with Hawkins bottom metal, it didn't work, it was on the cusp of latching but didn't.I’m running a 6bra and 6.5x47 Impacts in Foundation stocks. Both run Arc mags (with MK followers) flawlessly. Both also have 27 inch hv barrels and 419 brakes. It’s already been mentioned how smooth the Imacts are so I don’t need to expand on that. Joe at Exodus built both and these combinations flat out shoot.
I converted to AICS AI brand mags and haven't looked back.