Chris, the bolt lock is Part# 63 in the schematic. When the bolt is in battery, it's cammed up into a locking recess in the barrel tang extension. Shooting the gun with the magazine cap loose can damage these locking areas.
The Remington 1100 series that shoot 3" magnums, have one gas port, and usually don't cycle shorter shells. The 2.75" chambered barrels have two gas ports to cycle the shorter shells.
If all you have available is the 2.5" .410 shells, the single gas port can be opened up slightly to provide reliable function. The downside is, you can't shoot 3" after that modification has been done, or it will beat the action to pieces.