3 inch to 2 3/4 sleeve ????
 

I am building a mossberge to shoot at turkey shoots with modifications ive made so far am winning meat, but I stumbled on an internet article some time back of someone talking about a sleeve to shorten the breech from 3 inches to 2 3/4 inches to give just a small bit more of barrel length for possible improvement in accuracy anyone heard of or know where i can find info on this thanks,

I think that may be backwards. What kind of mossberg are you talking about? Besides, that 1/4 inch I do not see it making that much of a difference in the end of the chamber to matter.
I know of guys who lengthen the forcing cone to slow the tapering of the shotcharge during its travel down the barrel for improved patterns. Most higher dollar trap guns have this done and its improves both the pattern and the reduces the felt recoil.

Second Chance is right. Years back the NRA tested a "Long Tom" goose gun. I don't remember the exact increments, but they kept cutting pieces off the barrel and re-installing the polychoke. The length of the barrel had no effect on the range or pattern. I have had problems with guns having too short a chamber also.