Disaster!!!
Following a swift barrel change, gun was well down on velocity and popping its head off. Breech seal I thought so that was swiftly changed along with the two barrel o rings. Poppety pop pop pop, jam went my little friend. Bugger thought I. The first of the many reported Impact faults had raised its ugly head. Now sulking, I glanced down at the breech and thought to myself "bloody hell, that looks a bit large for .177." Yes, you guessed it, .177 pellets and probe dont work too well with a .22 barrel onboard. What a t--t I thought as fellow airgunners enjoyed much Mickey taking at my expense (especially a certain Mr Jones.) With the "proper" barrel installed the gun steadily chewed its way through yet more .177 pellets with its usual efficiency.
The moral of the story is dont let your spare barrel get sneakily changed without first double checking its calibre. Sorry to dissapoint the anti-Impact shooters!
Andy