Yup, the softer Federal primers will slamfire , especially if you DO NOT load it from the magazine.  :roll: 
Use your magazine to load the Federal rounds or ANY cartridges into your M14 / M1A chamber.  If you are at a range , benchresting your rifle, I like to load the nose of the bullet almost on the edge of the chamber ready for the trip forward.  :mrgreen:    Then Ill ensure the base of the cartridge under the right lip of the magazine.   :roll:   Then yank or slap that op rod handle rearwards and let the op rod fly forward.   8) 
Enjoy the M14 "music".  It's my favourite sound.  :wink: 
Hope this helps you avoid slamfires.
Barney