drover,
I like the way you used only 3553 fps for the 40-grain bullet in the .223 to calculate recoil, and 3701 with the 40-grain in the .204. In reality the .223 is capable of about 100 fps more velocity with 40's than the .204--which, of course, means the .223 will recoil more.
Do you actually load 40's down to about 3550 in the .223?
But while I've shot a bunch of 40's out of .223's. I much prefer at least 50-grain bullets, because they drift far less in the wind. They recoil even more than 40's, of cource, yet still drift noticeably more than 40's from the .204 started at 3700. Even 32's from the .204 drift a little less than 50's from the .223.
Plus, the .204 shoots flatter, which doesn't theoretically matter when you're dialing, but a lot of prairie dog shooting is at ranges where dialing isn't necessary. A .204 loaded with 32's at 4100 fps and sighted-in an inch high at 100 yards allows holding right in the middle of a prairie dog out to 250+ yards. A .223 doesn't shoot nearly as flat, no matter what bullet you load--but it doesn't even come close with 40's at 3550.
Of course, stocks shape, gun weight and the individual shooter makers a difference in seeing the target during recoil. My experience is also with a bunch of .204's and .223's, and for me (not you) I find that even with a heavy-barrel .223, with 50-grain bullets at 3400 fps the rifle doesn't come down out of recoil soon enough to see the bullet hit at any range less than about 150 yards. With a sporter-weight .204 I can see dogs hit at any range. It's easiest when shooting 32-grain bullets. This is all with scopes of about the same magnification, and hence field of view.
However, in my experience the easiest centerfire cartridges for spotting shots are even smaller, rounds like the .17 Fireball, .22 Hornet and .221 Fireball. Sometimes the reticle barely leaves the dog during recoil, which makes me think a .20 VarTarg may be worth a try. I've shot a couple of 'em but not a lot, and just might give it a try.
One last comment is that most recoil programs are too simplistic to provide exact results. I know this from measuring the actual movement of rifles during recoil.
But this exact subject was hashed over for many pages in the previous thread, a while back. You obviously haven't seen any significant difference in recoil between the rounds, while I have, which proves that we're all different in the way we shoot and hold rifles. But in the previous thread a clear majority said they could see hits better when shooting a .204, which I would suggest means there is some difference in recoil--especially when the .223 isn't downloaded.
