Posted ONLY for the sake of information:
I have been playing with the Grendel necked up to 35 caliber for almost two years now and I will tell you that I have ASC mags for the Grendel that swell when loaded.
Now: before anyone says "Of course they will swell, you have them stuffed with .358" projectiles!", let me say this: the datum line of the 6.5 Grendel is significantly larger than the ogive of the .358" bullet, so that argument won't wash.
I hope your ASC mags (assuming that is what you order) work for you. Just don't be surprised if they bulge after about half a dozen rounds and fail to feed, or even go into the magwell without additional effort.
Just my honest $.02...