i have one of the early PEPR non-QD mounts and it has been fine. i havent moved it in a few years and it has held zero on some hunts and lots of plinking with a bit of reflexive fire drills and such.
that said, i am far from hard on this rifle and that sounds like what the OP is asking for. if i were building a rifle to go to war with, i would buy LT QD mounts and better optics but a factory stag carbine with a yhm free float tube and a PEPR/Millett DMS combo is a different animal than a professional combat rifle.
now after 10 years of military experience as an MP and unit armorer through multiple combat deployments, i also doubt that 99% of the soldiers out there have gotten their rifles as hot and dirty as i have had mine and it has kept up fine, my stag that is. im a firm believer in taking care of my rifle though. full of sand or mud can happen but the likelihood is far less than most AR owners think it should be. and if something happens to your rifle that will cause even a PEPR mount to break or fail, then youre in over your head, imho.
"Only the dead have seen the end of war." - Plato