Went to the range today and fired a little over 100 rounds and 4 times the slide failed to remain open after the final round had fired. Could this be due to the target ammo? This is the second time I had fired my FNP-40, the first time was 50 rounds, so the gun has a little over 150 totals rounds through it. The gun was cleaned and lube both times prior to shooting. Did not happen the first time, only today. Could this be due to the gun getting hot? Should I give it a break between clips? Thanks for the help.