I recently bought 10 Barrett, 10 C Products, and 6 PRI waffle mags.
The Barrett mags are kinda all over the place. 2 of the 10 would drop free from a Colt SP1 lower, 6 would drop free from Rock River (which has my 6.8 upper installed) and Sabre lowers.
2 of the PRI mags would not drop free from my Rock River lower.
None of the C Products mags would drop free from my Colt SP1 lower, 7 would drop free from my Rock River lower.
All mags were tested empty.
I emailed PRI and they responded very quickly and replaced the 2 that did not drop free (I paid postage back to PRI). Now all of the PRI mags drop free.
I emailed Palmetto State Armory about the C Products mags (where I bought them) and didn't get a response. I figured with the frenzy, they are just too busy to deal with it.
I haven't contacted either of the places where I bought the Barrett mags. Frankly, I have 6.8 mag fatigue at this point and have other more important things to deal with.