Sounds like you might have something in your chamber.  Or you might have some cases that were shot in a 30-40 improved chamber.  Let me see if I got it straight.  Factory rounds will chamber, sized down cases will not.  If they won't go, they have to be bigger than they're supposed to be.  But unless the die is cut long, or you're not running them all the way into the die, full length sizing should take of it.  If the cases are already bigger than they should be, they may have been fired in a 30-40 improved chamber.  Even if so, full length sizing should fix it, but it would require a bit more force than usual, and perhaps some sizing die wax.  This is a hard one without some hands on checking of things!  Pic of a case that will chamber beside one that won't may be of help.

I have ran into a few rifles that were tightly chambered.  Not done by the Armory, but by someone else over the years.  Rental of a chamber reamer will fix that.  One that was short I could chamber a round, but it was pushing the shoulder back on an already full length sized case.  My reamer took care of that and it's now the same length as the rest of my rifles.  Oh, and make sure your FL die is not marked 30-40AI, the AI standing for Ackley Improved.