M2 ball ammo is the same whether it was linked or in en bloc clips. It is fully interchangable with either weapon as well as aircraft guns. What he had was probably deteriorated ammo since it was inconsistent. There is no reason in the world to be wary of linked ammo. CMP as a matter of fact sold tons of delinked .30-06 a year or so ago. It is fine to shoot in a rifle. By the way, using military ammo does not require an adjustable valve at all. It is the commercial ammo that is too hot and requires the adjustable valve.