I put a 5/16 steel plate at 400 yards. I shot it with a 22-250 55g VMax's, .243 85g Sierra BTHP's, and .223 50g Ballistic tips. The 22-250 55 VMax's did the most damage (Black circles), then the .243 85g BTHP's (Red circles) and the .223 50g Ballistic tips (Blue circles), didn't even put a dent or knock the paint off. I expected the .243 to do more damage than the 22-250 but the test proved me wrong.
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Impact energy is what works on steel and that goes to velocity, every time.

I agree but in this case the velocity at 400 yards should be - or could be - about the same between the 22-250 and the 243? It might be that the smaller diameter of the .224" bullet at similar velocity to the larger diameter bullet is a factor?

Check/compare the sectional density...

"I agree but in this case the velocity at 400 yards should be - or could be - about the same between the 22-250 and the 243? It might be that the smaller diameter of the .224" bullet at similar velocity to the larger diameter bullet is a factor?"

Possible of course. Since we don't KNOW our guesses are just guesses!

Hadn't considered the velociy loss at 400 yards would make then virtually equal. You are right, so that's out.

NOW I'd guess there is significatly different construction so the .22 held together better? I mean, no matter how hard you throw an egg it won't make the same impresssion as a golf ball at the same speed. ??

Sectional density considerations only come into play if construction is the about the same.

Just thinking out loud,

I read a post that said a 17 M2 is supposed to shoot through a nickle at 50 yards. I can't say if that's true? The 22 Magnum has similar velocity depending upon the load used. Not knowing, I'd venture to bet the Mach II would penetrate steel better. Kind of the same test on a smaller scale.

Only one way to find out.......

Red, when I go back into the mountains next week I will try it and post the results. If I remember? CRS is setting in. AL

Interesting!