I have bought two Marlin '93 rifles in 32-40 cal. The first one with a bore that looks like it ought to shoot keyholed bullets--new Hornaday case, 14 gr 4227--with .321" dia bullets and also Winchester jacketed loads at 50 yds. Slugged both bores, measured .324 grove dia.
Attempts to make cerrosafe chamber cast unsuccessful. Two casts exactly following Brownell's direction, neither would be pushed out of the bore even with a long brass rod and a hammer. Each time I melted out the cerrosafe--fortunately an 1875 watt heat gun melted the stuff. Acts like it was soldered into the chamber. I decided a chamber cast will not work, so I made some paperpatched bullets which show that the chamber will accept a .326 bullet.
sized bullets, both grease-groved and paper patched and loaded them into carefully neck expanded cases. Cases will not chamber because with the oversize bullet the neck is too big dia for the chamber. Using a sizer die as a taper crimp die, reduced the dia of the neck to SAAMI specs and the cases chambered perfectly. Of course the crimp also resizes the bullet.
I now see that the bullet which fills the chamber ahead of the case is oversize, but the chamber neck is too small to allow the oversize bullet load to chamber. Weather has not permitted me to get to the range and my new loads, but assuming they don't shoot accurately, do I have any alternative to honing the neck area of the chamber and a sizing die to accept a larger bullet?
since I have two rifles with the same bore and chamber dimensions I assume Marlin used these on its 32-40 rifles. How did deer hunters in those days shoot commercial ammo in these guns ?