So I'm new to FN firearms. I bought this FNP 40 a few weeks ago "gently" used at the gun show. Took it to the range the next Sunday and though it shot excellent however it would not leave the hammer cocked after the slide cycled when firing around 90% of the time. Maybe 2 of 50 rounds were fired SA. I thought it was just crappy ammunition, Monarch brass 180gr. So today I shot another 50 of Federals aluminum 180gr. About 25% of the shots re-cocked the hammer and allowed a SA pull. Are these pistols that finicky or is there a repair necessary? Input is appreciated. Thanks!