Try out a different brand of ammo. Could be hard primers.
Alternatively, disassemble the bolt and clean the firing pin and its channel of any accumulated grease. Grease can slow down a firing pin such that it doesn't have enough energy to ignite the primer. Check the firing pin for burrs and polish it out if there are any. Also, after you clean the firing pin channel, shine a light down from the bolt face to see if there's any burrs.
Another possiblity could be whether the trigger housing unit has been drilled correctly for the hammer pivot pin. If it's off, the hammer won't transfer as much energy as it should.
Finally, make sure the bolt is fully locked up before squeezing the trigger. If it wasn't, the gun shouldn't fire (out of battery). Op rod (slide) could be bent or out of spec.
Vigilantibus et non dormientibus jura subveniunt
[This message has been edited by 4V50 Gary (edited November 22, 1999).]