Elftmann is the only brand that I have enjoyed any success with in the APC series of rifles and carbines. I tried Timney and Trigger Tech "cassette" type Trigger Packs as well as different Geissele Trigger systems in my APC 308 - all with no joy. The problem is that the custom "Match" Hammers all bind against the bottom of the Bolt Carrier, which runs considerably lower down towards the Trigger Pack when placed in an APC rather than would be the case in an AR15. Even with the Elftman, all may not be perfect as mine just started acting up with the Trigger not seemingly resetting. Investigation turned up the problem immediately - a broken rear Trigger Pin, which locates the rear end of the Trigger Cassette in the correct position. I am not sure why the Trigger Pin broke, as it ran for at least 500 rounds before failure. I swapped around the broken pin with the good pin and everything is holding together and functioning fine again, so back in business with more Trigger Pins on order from Wolverine Supplies...