Thanks, I'd never heard of that product

Update...

I changed the spring with a stiffer, RRA carbine spring (stronger spring than DPMS/Colt). With the H buffer, I got a little blow back, but no where near as much as with the lighter carbine spring. When I added a 9mm, 6.5oz, buffer, it completely stopped the issue.

HOWEVER...now it's too heavy to cycle the loads I had out for testing today. I didn't bring any of the AA1680 with 10.6gr and Hornady 225's that I had been shooting because they have been exiting the bore in transonic speeds in both the 8" and 16" barrels I've got on the AR's.