Here is a Q & A I found on another forum...
Q> My question is: do I need to change the breech to change caliber, or just the barrel and bolt?
A> Just the barrel- the stock Crosman bolts are the same size (.177 vs. .22).
Q> .... but although the bolts are the same size body, aren't they different at the front end...., they have a different taper on the front and a different O-ring to seal against the end of the barrel
A> I have yet to hear anyone who has noticed from a performance perspective. Don't get me wrong- perhaps when using the "correct" .22 bolt in a .177 barrel it will be a bit tighter pushing in, and likewise the .177 bolt may be a bit more loose, but it seems the difference has never been enough for anyone to notice without breaking out their calipers.

This just doesn't seem well founded to me... And, I do not have time, before leaving, to do all the bolt and barrel switching and am not even sure how I would measure the difference in performace. Use a pressure guage? A temp guage? A temp of the pressure guage? ha ha ha. (Just kidding of course.) Certainly a CO2240 is not adequate to measure the differences. I think it would take HPA or PCP setup to be able to "clock" the results on a chrony.

IMO, the A guy is way off and I can hear a 177 bolt rattle, metal against metal, in the 22 chamber/breech/loading port, whatever you want to call it. I can also see the difference between .1905 inches and .240 inches when held next to each other. Or, possibly, this is another situation where my parts are not the same as everyone elses?????

Anybody got the right gear, or, inclination to do a myth-buster on this one? I would be happy to use my extra 177 bolts in the 22 Bbls. But, will I be suffering performances losses?