With all due respect to those who have posted , Military brass in most cases is thicker but not always . newer ammo from off shore seems not as thick but harder . It must contain a pressure level and that is the spec that must be met . Primers , CCI 34 primers or equal are used in standard military ammo from the USA. Why ? because the M1's and M14's both have free floating fireing pins . When the bolt is released and a round is chambered the fireing pin strikes the primer and if the primer was of less thickness a slam fire could occure. Check it out if you or a frind has one just release the bolt and let it go forward under its own force or fire a couple shots then remove a round and in most cases there will be a slight mark where the fireing pin struck the primer. I got alot of brass that was military , Lake city and Winchester . It had been fired in a machine gun . After resizing several hundred , knocking out primers and removing the crimp I can assure it was way harder to size than commerical ammo.
Good reloaded ammo can be shot in a M1-A or M1 with out damage if like mentioned it meets the spec for military ammo , I use 150 -165 weight bullets and try to match mil spec ammo in other respects. ( yep I use all CCI #34 primers and even on a AR 15 use #41 primers which are the small rifle arsenal primers and yes the AR has a free floating fireing pin ).
I would note that in a military gun the rim on some commerical or off shore ammo may be soft and military guns can strip thru. the rim if the chamber is dirty or sticky. The militar rounds I loaded were supposed to have come from full auto fire , some M 60 other M 14 alot had bent rims , some would not go into shell holder . Once they were reloaded and fired the rim got stright , yes it was hard closing the bolt on some , a few were disguarded .
bullet jacket is a concern I have because I have a model 70 winchester in 3006 that had a bit of mil surp. ammo with steel jackets shot thru. it and the bore is showing alot of wear and group size is expanding. Some steel jackets are made of softer steel than barrel steel while I wonder about off shore ammo .
Some new ammo is steel cased not sure how that will work out.
I tend to stay away from off shore ammo from places that don't sell quality commerical ammo. Back in the early 70's one of our biggest gun stores at the time had loads of surplus ammo for sale . I was poor so it looked like a deal . They had what was supposed to be 9mm ammo manfactured in the early 40's . It came from somewhere in the middle east ( at the time there was a book that showed head stamps and that is where the info came from) at about 3cent a round what could go wrong ? Well 1 in three might go off , it was non reloadable and if you waited over night to clean your gun it rusted. Fast forward to the late 90's same store , 7.62X39 from China great price ammo scarce due to Y2K. one in 5 failed to fire. There have been other examples where one round went bang, next one boom . I just hesitate to buy off shore ammo anymore.
As for advertising the NATO stuff it's so M1-A type rifle shooters can know it meets mil spec. That said there are lots of commerical ammo set up for match shooting with M1 , M1-A and other such rifles and I don't have a clue what primers they use . But in most cases the rifle will be level and pointed down range when the bolt goes home not pointed down allowing gravity to help. BTW I have been told military rifles don't have inhert fireing pins ( a return spring to avoid slam fires ) because it could break and cause the fireing pin to be blocked and not work.
Now some will say the free floated fireing pin is BS but I have witnessed a SKS with packing grease around the fireing pin that was stored in a truck over night in one diget temp. that evidently when put in the truck with empty chamber and muzzle down froze with FP sticking out in front of bolt face . As the shooter released the bolt the gun fired all ten rounds . The shooter put two rounds in and it did the same thing a couple times more so he stripped the bolt cleaned out the grease and all was fixed. Keep in mind the trigger had not been pulled.
I only mention this because so many people who have no training on military type weapons are buying them these days and they really need to know what they have and how it works and why it's built as it is.