I have seen this problem many times and it is always firing pin related. I always check around the chamber end to make sure the barrel has not been penned by a kid dry firing. If that is the problem you will need a chamber iron. Not hard to make if you have a lathe.

I have over the years seen a lot of broken firing pins in the M-39's. I only have two 39's but keep a spare pin on hand.

Thus saith thr lord; Cursed be the man that trusteth in man, and maketh flesh his arm, and whose heart departeh from the lord. Jeremiah 17:5 KJV