11/11 RM gunners with full experts and a boost cap accuracy at lvl 108. Without a boost they wont cap without 10 vets at lvl 120.

Earliest you could cap them with 100 vets, a boost and full experts, is lvl 88. You could cap earlier with even more vets though ofc.

There's no trick, just more experts, vets, boosting and leveling. They will eventually cap, just very late.