Shell sticky could be pressure related, the federals may be hotter then the rems therefor case expansion is such that it sticks until cooled slightly. Can be a result of a burr (s) in the chamber. Did you notice any marks on the spent cases?? This is a sign you may need to touch up or slightly ream to remove.

Other option is try different ammo, you know rem corelokts aren't good, federal x stick..so try a 3rd option?