Khan;
A normal chamber for the 12 gauge shotshell will have .005" per inch of taper to it to facilitate extraction/ejection. Thus a 2 3/4" chamber will be .014" bigger at the rear than at the forward end where it joins the cone. Current minimums are .798 & .811" I believe. I will assume your chamber was cut to .799 at the forward end & with the .014" taper should go .813 just ahead of the rim seat. Any factory new shell or proper reload should enter easily & should not stick.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra