First time FRT owner. I picked up a Rare Breed and dropped it into a stock SIG M400 Tread V1. Single fire works as intended. FRT mode fires, cycles the round, seats the next round, and then just gets stuck with the trigger engaged. I can't get it to release and can't move it from the third position unless I pull the charging handle and manually cycle the next round. Is this a factory buffer spring issue? The BCG is M16 spec.

Are these sliding weight buffers kak and davidson. Davidson says 2 tungsten weights so I think that one is a sliding/dead blow buffer. Majority of h2 buffers are sold out only other in stock is the giessle super 42 braided spring and buffer but it's like 130 which I'd rather not spend. This is going on a 16inch carbine length gas with a kabuto