How did you get a 3" shell into a 2 3/4" chamber?
a 3" shell will chamber in a 2 3/4 chamber easily because of the slanted front of the chamber area to make room for the unfolded crimp after firing. A 3" shell will not have than room for the fired crimp and usually ups pressures.
I think I recall the LT 20 frame is not the same as the regular frame, either way the barrel is cut for 2 3/4 " shells.
You can have to barrel rechambered for 3" shells easily
