I’ve had boringly-reliable performance with ASC mags made in the last 5 years, the 25rd ones.
I’ve shot those mainly through the 12” Grendel, CLGS, suppressed 100% of the time.
Same with Amend2, older CProducts, Elander, and whatever else I have dating back to 2009.
ASC and Geissele allow the longest COLs, with the Geissele mags taking the cake at well over 2.300”.
The Geissele mags have a single laser weld on the spine, with only one layer of sheet metal on the front wall.
They look like ASCs with a laser welded spine basically and no front spot welds.
Metal mags are mostly 2 halves welded together front and back, which adds thickness to the front wall, robbing you of room to play with if you’re chasing longer COLs.