(My apologies to the small caliber forum readers who will see this posting twice.) I just bought a large frame Martini that was converted from .577/450 to .22 by relining. Then it was chambered in .22 K Hornet and the action converted back to centerfire. Anyway, the previous owner fired factory .22 Hornet ammo with .224 diameter bullets in the original .22 rimfire bore. I haven't fired it yet, but will try to obtain some .223 diameter 45 grain bullets for it. Neither have I slugged the bore, but .22 rimfire bores usually measure .221 groove diameter. It probably has a 1/16" twist, so lighter bullets at 40 to 45 grains will be where I start. I have .22 Hornet dies but they are made for .224 bullets. Am I going to need a smaller button for the case neck? I may try at first to fireform standard Hornet cases and then back off the die to neck size only if there is enough room for the case. Before I make all of the mistakes everyone else has made in this situation, does anyone out there have experience loading for a Hornet or K Hornet with undersized bore? What are your recommendations?