Please note how I worded the nomenclature of this ammunition.Just a little explanation.7.62X51NATO surplus ammunition and .308WIN commercial ammunition are not the same.The rounds look identicaL and will chamber in the same rifle.The specifications of size are almost identical but there are differences in the overall length,loadings,types of primers used,projectile makeup,pressures generated and shell casing thickness.
The overall length in most cases is greater on a 7.62X51 round.This will create less freebore in a .308WIN barrel.
Loadings of a .308WIN commercial are much more consistent and normally create about 25% mopre pressure than the military round.
Bullets are not as consistent insofar as weight consistently from round to round in military ammunition.
The military rounds use "hard" primers creating sometimes a failure to fire of a perfectly good round in a commercial rifle.In a lot of cases a round which will not fire in a commercial rifle will fire in a military rifle.Do not automatically assume that a round is a dud just because your relatively weak commercial firing spring will not generate enough punch to detonate it.
Brass thickness is much greater in the military round which has an effect on load and performance of the bullet leaving the casing as well as expansion of the round in the chamber creating an effective gas seal.
Some manufacturers void the warranty of a rifle if military ammunition is fired in it and an advisory of this is included with a new rifle but may not pass down to subsequent owners.H&R includes such a warning with it's rifles which will fire military rounds such as .223 and 7.62X51NATO.
As a kind of recap,I shoot a lot of military ammunition but I do not expect it to be of the same quality and therefore accuracy as the commercial counterpart.The surplus is cheaper.It is fun to shoot.Just don't expect it to be anything more than plinking or blasting ammunition.
There are several types of surplus I have found that does not perform very well and I stay away from it and there are a couple of good types.
The best I have used are the Portuguese made by FNM , the Australian and American.The Indian really sucks having delayed fire and duds.Any Pakistani is junk just like their .303 ammunition.
Be sure that you rifle warranty does not exclude firing military ammunition and whether or not you wish to heed that.