Just a footnote, & to get back to the original question, 'Where do I start?'

Just before my Grandad lied about his age & joined the army in 1914 he'd bought a BSA Improved Model D. airgun. When he got back from the trenches some years later he'd lost interest in guns somewhat & it stayed in the cupboard until he had to keep his infant grandson amused, we spent many happy hours creeping about behind the rockery while he taught the rudiments of trench craft & sniping to a 3 year old me.

BSA Improved Model D, .22 of course - that's my answer.