OK guys need alittle help. I just bought a Del-Ton AR15 HB used but appeared to be unfired, stopped by the range on the way home put 40 rounds through it worked fine, this was Wednesday, Saturday took back to the range noticed I was getting double taps when I fired,realized that when I fired then let off the trigger it would fire again? Looking to order a new trigger group but dont know if it is large or small holes? Seems to be the same size pins as my DPMS AP4, Never built or taken apart AR's before to know the defference. Any help appreciated. Thanks