So many things .It was always a problem if someone else had been at it in the past , but if you have had the gun for some time tis is probobly not a factor here .
A gentle cleaning would always been my first thought .
Also check that the safe was not going on on firsts firing .
Check that the trigger is not fouling the guard bow and that it is coming fully forward .
After that it is a matter of checking springs and that any moving part is functioning .
The amount of recoil is also a factor in some older S/T's .
Loose stocks or trigger plates can be a cause , or for that matter if the trigger plate has sunk into the wood due to age and had the hand pin pulled up .
Hope its something simple !
May I also comment on Teds mention about Spanish single triggers ? In so much as AyA used a S/T that was a close copy of a Miller trigger .
