Can anyone advise please. The bolthead on my SMLE jumps out of the groove when cocked or dry fired, don`t believe this is normal. The rifle is a mix of parts and numbers. The bolthead itself is stamped with a U, which I believe is Sth African. Is there a cure for this problem? Any help would be appreciated, as its a nice looking piece and this tends to spoil it when i`m showing it off.