For anyone planning on running an ATRIUS selector, here's what ive compiled as necessities thus far

1 millspec trigger with a flat rear shelf, the PSA enhanced polished trigger seems to work great.

2 filed flat rear of carrier group for good sear interface, If the back shelf of your bcg has a slant, slope or curve you need to file it flat so the trip sear engages on a flat surface and doesn't get bent, this is what was causing all of the leavers breaking previously.

3 H2 or H3 buffer WITH shake in the buffer weights, a no rattle/ no shake buffer will result in bolt bounce and lead to out of batteries or light strikes.

Follow these steps and you should have good results.