.....don't let me talk you out of what you really want. Or better yet, get both and test em out to your own satisfaction. Nothing better than shooting, lots of shooting!
If you can get enough pressure behind a heavy pellet or light slug in .177 it would be the best option , something I can play with on my .177 Webley Rebel pumper this weekend think it is the only high output .177 pumper I have ATM
To answer your question, with my personal opinion, never. I like the bigger hammer that the 22 is. It shoots plenty flat at reasonable range, so thats a wash. And at any range it hits harder with double the weight and more frontal area. But thats just my opinion, don't let me talk you out of what you really want. Or better yet, get both and test em out to your own satisfaction. Nothing better than shooting, lots of shooting!
Not a Crosman - but I have gotten an Avenger .177 and shoot 10.5gr Crosman domes - it is the .177 pest gun I use.I also use the .22 Fortitude
I am not to sure I am in favor of 18-20 pumps - I only pump mine 4 to 10.
I have a 13xx lower with a modded OEM valve, pinned. I also have a lower with a Mellon FTP kit. The cool thing about "Lego" guns is that you can change out barrels easily.As a suggestion: Build the FTP lower and figure out what you like best - keep changing until you find what suits your needs.
I'm not sure at what velocity one is better than the other. I have a highly modded 1322 that does 600 fps with 14.3 grain pellets with 15 pumps. 560 fps with 12 pumps. 535 fps with 10 pumps. 410 fps with 5 pumps. A 14.3 grain .177 grain pellet will always be slower than a 14.3 grain .22 pellet because there is less volume in the barrel for the air to push the pellet and less surface area of pellet for the air to push against (at least that's my simplistic understanding). I have a benjamin 397 that does about 610 fps with a 13.4 grain pellet, but my benjamin 392 does about 645 fps with a 14.3 grain pellet. of course those are different guns and there's variation gun to gun, but think it does demonstrate the principal of the matter. theoretically, a heavy small diameter pellet though pushed at a slower initial velocity should retain velocity and energy better than the larger diameter pellet, but I think you would never see those gains in something like a 1322 pistol, since either caliber would be a relatively short range proposition.