The shell will hold the slug centered in the barrel well enough to make the 1/4" jump to the barrel throat without difficulty.
Regarding shell lengths, you can use shorter cases in a longer chamber without problems. But you can't use longer shells in a shorter chamber, ie a 3" shell in a 2-3/4" chamber. The reason being that even though an unfired 3" shell might fit in a 2-3/4" chamber, there won't be any room for the crimp of the shell to open up inside the chamber - and bad things will happen.
Remember - that shotgun shell length is the measurement of a FIRED case, after the crimp has opened.