ANY BOXER PRIMED 7.62 NATO brass that has nor been shot out of a machine gun, is usually acceptable. If you use IVI, sort the cases by water volume, otherwise there will be some rather large variations = not so consistent accuracy. Some of the best 7.62 NATO ammo for the 14 is Hirtenberger, and the brass works well.
Do NOT expect a high nimber of reloads from your brass ... the M-14 is hard on brass, especially if you are shooting on concrete, or if you have a genuine M-14 op rod [ designed to motivate the brass during ejection ].
I personally don't want to load for the 14 any more, and would rather trade gunsmithing for factory loaded ammo. That way, I get a bit more than $ 5.00 an hour for my time.
[;{)
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