There are several answers/solutions for this one but I believe your problem isn't so much too much hardness but too rough a sizer die. I polish all new sizer dies, reguardless of brand before even trying them, because none I've used were as smooth as what I like.
Most hardwares sell buffing compound and the one you need is Dico brand Stainless. Stainless is the grit designation, and it is white. You'll need a high speed grinder to do it right, (dremel is fine) but a 2000 rpm electric drill or drill press at top speed will work fine. Split a 4 inch long piece of rod that will fit your grinder and be well undersize for the die to be polished. The split goes lengthwise for about 3/4 inch with a hacksaw. Insert a strip of cotton cloth through the slot and wind a 'polishing bob' unto the shaft. Of coarse it must be wound so the turning machine keeps it tight, normally the shaft turning right hand. The bob doesn't need to be a tight fit to the die, just a good pad of cloth. Rub this bob against the white compound while spinning at high speed, until you see the cloth become coated. (The compound melts with the friction.) Go into the die with this and work it over good wherever you think it needs shining up. Don't worry about wearing it oversize, as you'll really work to earn even one tenthousandths of an inch. Work the taper into the sizer especially throughly as this is where the sizing is done. --- Your bullets should size with 1/2 the effort or less and pop out easy after this treatment.
On a few occasions I have had water drop hardened wheel weight bullets turn up a roaring 35 bhn hardness! Though I could not repeat it on demand, I believe it was because the water nearly froze that night soon after the casting session. You may have a batch like this, but they will size just fine.
If 460 bullets will chamber in your gun, by all means don't size them smaller. You'll get best accuracy with them fat in most 45 cal rifles.
If you believe they are too hard yet, you can soften them by heating in a kitchen oven to about 250 deg for one hour. Cool any way you like as it won't effect hardness from this temp. You can experiment with the temperature, changing 20 deg per trial. e.g. heat only a couple at 250 for the prescribed time, quench and try sizing. If too hard, up the temp 20 deg and try a couple more, or if too soft, drop the temp 20 deg, etc, etc, until the desired hardness is obtained. Then run the whole lot. If they are already lubed don't heat them in your wifes oven unless you want a divorce. I won't guarantee it will give you one, but will assure you that it WILL make your life miserable for a while!
You can reheattreat them by heating them to 400 deg in the oven and water quenching. Then to make sure they run through the sizer easy, blow dry the bullets and size within 2 hours after the quench.
