Quote Originally Posted by majex45 View Post
The answer lies in the rifling:
If the pellet size is .177 and the rifling is .0025 deep therefore the land size is .172 which is a fraction over 11/64 inch so the barrel could be drilled with an 11/64 drill.
For .22 pellets the barrel drill is 7/32 (.218) giving 2 thou rifling.
Mmmmm - i like your thinking....
....possibly...
BUT: what a 'weird' unit to begin from anyway. It just seems so 'arbitrary'.

Can anyone prove to me whether .22 as a rimfire (be it short, long, CB, etc) predates .22 as a unit for air rifle? Should be easy - shouldn't it?

Odd isn't it - that in early 'British' air rifles the No.1 (.177) load is prevalent over .22 - yet in the US it seems to be the reverse.