The .223 to .22 WMR gap is maybe worth discussing relative to the SAAMI data.
The.22 WMR shows the following loads (all velocities in a test barrel):
28 gr JHP (lead free), 2175 fps
30 gr JHP, 2200 fps
33 gr PT, 1950 fps
34 gr JHO, 2075 fps
40 gr FMC, HSP, SP, 1875 fps
45 gr LHP, 1550 fps
50 gr JHP, 1650 fps,
The maximum average pressure (MAP) for the .22 WMR is 24,000 psi, but because the .22WMR is noted to have much more variation in pressure than .22 LR, it has a 2400 psi standard deviation with a maximum probable sample mean (MPSM) of 27,800 psi.
SAAMI data for the .22 Hornet shows the following loads:
33 gr, 3040 fps
34 gr, 2985 fps
35 gr, 3040 fps
45-46 gr, 2655 fps
The MAP is 49,000 psi with a MPSM of 52,100 psi.
SAAMI data for the .222 shows the following loads:
40gr, 3370 fps
40 gr, 3570 fps
50-52 gr, 3110 fps
55 gr, 3000 fps
The MAP is 50,000 psi with a MPSM of 53,200 psi.
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There are not many apples to apples comparisons in terms of bullet weight, mostly because the SAAMI data does not show a 40 gr load for the .22 Hornet. In my own experience I get a an average velocity of 2,857 fps with the 40 gr V-Max in a 20" barrel and that's in the ball park for factory data for similar 40 gr bullets - 2,850 fps for the 40 gr Nosier ballistic tip, and 2800 fps for the Hornady 40 gr VG FB.
Consequently with a 40 gr bullet you get:
.22 WMR = 1,875 fps
.22 Hornet = 2,850 fps
.222 = 3,570 fps
That puts the .22 Hornet 1000 fps over the .22 WMR and 700 fps slower than the .222.
Practically speaking, the .22 Hornet works better when launched a little slower, and despite getting superb accuracy with the Hornady 35 gr V-max factory load (3100 fps published, 3009 fps in my 20" rifles) I find my best accuracy at around 2700 fps with the 40 gr V-max and 2770 fps with the Barnes 30 gr VG (although I don't pay much of an accuracy penalty at 3017 fps with the 30 gr VG).
That puts the .22 Hornet squarely in between the .22 WMR and the .222.
Ballistic data shows the following:
.22 WMR Remington 40 gr JSP at 1910 fps
161 yard point blank range (+/-3") with a 140 yard zero, 6" low at 200 yards, 12" low at 250 yards and it goes sub sonic at 161 yards.
.22 Hornet 40 gr Nosler ballistic tip, 2,850 fps
260 yard point blank range (+/-3") with a 225 yard zero, 6" low at 290 yards, 12" low at 325 yards, and it goes sub sonic at 550 yards.
.222 Remington 40 gr Nosler ballistic tip, 3450 fps
306 yard point blank range (+/-3") with a 265 yard zero, 6" low at 340 yards, 12" low at 385 yards, and it goes sub sonic at 690 yards.
In that regard, the .222 doesn't gain all that much over a .22 Hornet, but the .22 is able to launch a heavier bullet at .22 Hornet trajectories:
.222 Remington 50 gr Nosler ballistic tip, 3025 fps
275 yard point blank range (+/-3") with a 240 yard zero, 6" low at 305 yards, 12" low at 350 yards, and it goes sub sonic at 640 yards.
.222 Remington 55 gr FMJ, 2789 fps
250 yard point blank range (+/-3") with a 215 yard zero, 6" low at 275 yards, 12" low at 315 yards, and it goes sub sonic at 510 yards.
So the advantage of the .222 over the .22 Hornet in terms of practical field performance is 12-15 grains more bullet weight with the same trajectory, or alternatively, about 60 yards more effective range with the same bullet weight.
But the .22 Hornet gives you a 100 yard range advantage over the .22 WMR and it gives you some better options in terms of higher BC and reduced wind drift.