Fire Forming Question
 

I'm new to fire forming but am about to make the plunge. I will first be loading 22-Hornet ammo using new, unfired brass and firing same through a 22 K-Hornet barrel. The resulting brass will be formed to the K-Hornet barrel and I'll then be able to "kick it up a notch" the next time I reload same. My question is: Must I size the new, unfired brass, given that it will be rattling around in the 22 K-Hornet barrel anyway? I was hoping that I could check size by dropping a few un-primed bass in the barrel and, if they seemed to fit OK, check only for length.

In a cartridge that headspaces on the rim, like a 22 Hornet, you don't have to worry about the case fitting the K Hornet chamber.
My suggestion is this: get some advice on what makes a good load for fireforming from someone with experience with the K Hornet ( like Rocky), load the recommended load, and shoot it.
Proerly fireformed cases will be the result.

I'll recommend Hodgdon LilGun as your powder AFTER you fireform, but it is a low-pressure producer in the Hornet, and might not give you fully formed cases the first time. Instead, try a regular load of 4227 from the bullet maker's manual. Just load the maximum load or a bit under, not the Start load as you usually would. The extra work to blow out the case and the subsequent larger volume will take a lot of the "steam" out of the first firing. I use Rem 6 1/2 (NOT 7 1/2) primers in the Hornet.

After forming, switch to LilGun at about 13.0 and work up to a casefull if your primers stay tight. Stick to the mild 6 1/2 rifle primer or even the CCI small pistol primer. And if you don't have one yet, get a Lee Factory Crimp Die. Most Hornets group much tighter with this primer/powder/crimp recipe.

Rocky
You took the words out of my mouth (barrel?) 13 gr LilGun, CCI small pistol primer.I seat mine long to fit my Encore and Lee crimp. Head-shot accurate.