Ya, you have to kinda force the trinity in.....the orings on it get caught on the threads sometimes. I found that oiling the threads up a bit helped.
If that's not the problem, then I would ask if your gun is new? If it isn't someone may have altered the treads to fit another reg before you owned it....
ETEK 3LT, with 14" critical .680 barrel and cure 3 + bolt F/S
DM12 red with matching Boomy F/s