Some mfgr shells, the 'brass head' actually steelon most all hulls made today is a bit springy as compared to others.
Since theya re all being sized by the same sizer die, they are all being swaged down to the same dia.
But some will spring back a bit more than others.
Those are usually the ones that chamber almost all the way but then refuse the little bit.
I used to have trouble with a certain Winchester 20ga promo hull. Can't remember the actual marketing name of the load. They loaded real nice but they would
refuse to chamber in one particular gun. Win AA hulls, Federal , Remington reloaded on the same press had no problem.
Also, the mouth of the reload can sometimes have a mushroom type look to it and that can prevent it from chambering all the way.
The final crimp die on the press is supposed to do just that (final crimp) but also give a slight taper to the end of the reloaded shell.
Sometimes a simple readjustment of the final crimp die resolves that.
Make sure the pre-crimp isn't overdoing it's job. Too much pre-crimp can cause a bulge just below the final crimp that sometimes can't be made to dissapear
by that that final crimp stage.