Well, I'm afraid I've got bad news!
It's almost impossible NOT to fireform brass perfectly for the K-Hornet!
Load the rifle with any standard Hornet ammo, point it downrange, and pull the trigger! Perfectly formed brass will pop out of the chamber!
Seriously, the only thing you have to worry about is trying to form brass that is old-that is, brass that has already been fired and reloaded many times in a standard Hornet. Work hardening the brass makes it a little more brittle, and the case will split at the shoulder rather than form to the chamber perfectly. Almost all splits can be avoided by using new or once fired brass to form to the K-Hornet.
I suppose if you're really cheap, and have a lot of often reloaded brass for the standard Hornet, it is possible to anneal it before fireforming. I'd just form new stuff and avoid the hassle.
Proper procedure, actually, is to size the standard case just enough that it is a snug fit in the chamber, with a little "feel" when you close the action or bolt. The case is then headspacing on the secondary "shoulder" formed where the sizing of the neck stopped.
Trouble is, the standard Hornet case is so steeply tapered that it's questionable if it really headspaces here when you're doing this. The rim is actually providing the headspacing, and it's really hard to goof up the fireforming of a rimmed case.
Sorry for the long post but I though you needed a little of the theory behind fireforming to put your mind at ease regarding any difficulties with the K.
Incidentally, if you are a bullet caster, a moderate charge of the faster shotgun-type powders (Red Dot, Unique, etc.) with your cast bullet is a much cheaper way to form cases than using jacked bullets a 7-10 cents a pop.
I know you'll have fun with it. Just seeing the new case shape come of the chamber is entertaining in itself!
