Regrettable, Mobuck, but tens of millions of ancient rifles have performed with no problems due to faulty metallurgy.
Sure, rifles made late in a war by the losing side had problems. The Nazis began having sabotage problems in 1943, which increased in 1944--which provides cutoff dates.
The Japanese rifles' quality declined by sometime in late 1944, from what I've read.
You're from BATFE? Come right in! I use all your fine products!