Just wondered if any other manufacturers (not necessarily gunmakers) around these times was already making tubing with an internal diameter of .177. That way perhaps if an experimenter wasn't into barrel making they could source some tubing or perhaps commission a maker of tubing to produce some with a thicker wall more suitable to their requirements for developing an 'airgun'. I'm not saying an airgun inventor wouldn't or couldn't produce their own barrels but if there was already some sort of tubing available it might free them up from one aspect of airgun development, & if the size chosen was already established for one use or industry, then maybe it could conceivably become adopted or adapted for use by a new one.& if it was already common in one industry then perhaps it might explain how .177 caught on & spread...? Don't know, just a thought ...