I have measured such bullets both as components and in factory loads, and have seen results from .227 to .228! But have also seen larger-caliber caliber bullets vary as much as .001 in diameter as well, so apparently it doesn't really matter, probably because rifle bores and grooves also vary slightly. In fact I have seen some .303 British rifles, which generally are .311-.312 in groove diameter, shoot .308 diameter bullets very well.
However, I've handloaded for two old Savage 99's in .22 HP, and neither one shot the Hornady 70-grain .227-diameter very well. I later was told (not by Hornady) that it was actually intended primarily for the 5.6x52R cartridge, the Euro-equivalent of the .22 HP, which at least used to be pretty popular for hunting smaller big game over there. 5.6x52Rs apparently normally have about a 1-10 inch twist, while 99s have 1-12 twists, and apparently the 70-Hornady is right on the stability bubble in a 1-12, something some twist formlas have confirmed.
I did a bunch more research, and eventually reconfirmed what Ken Waters discovered a long time ago: .224 bullets shoot fine in .22 HP's, though they probably allow some gas blow-by in the grooves, which might result in more erosion. I never shot my old take-down 99's much as prairie dog rifles, however, and my "pet load" eventually used the 60-grain Nosler Partition, which may have bumped-up a little due to the exposed rear core. Whatever the reason, whether twist or core-bump, it shot very well in my last .22 HP, and of course worked fine on big game.
