Just to throw a curve to this topic.
Years ago my gunsmith friend had a .20 cal Sheridan Silver Streak pump up rifle.
There were not many good pellets available so, being a bit anal, he made a bit of kit to sleeve down .22 to .20 to suit his barrel.
It was very accurate and hard hitting!
I asked him at the time about calibre for the rifle I was getting he said .177 but if you could get a good .20 cal it would be the best option!
I went at the time for .22
So my question here is why has no manufacturer ever bothered with .20 cal in air powered rifles?
Incidentally he made a cus