I seem to recall having read in the past, perhaps Greener, that the tubes were rough bored, but not to finish size. Would not have had any choke at that point. The breeches were threaded as I recall & a breech plug with touch hole screwed in. The large proof charge would have then been muzzle loaded. The barrels were then laid on a frame with a powder train connecting them. A large number of tubes could be proofed at once. When the train was touched off the tubes fired & recoiled into a sand pit behind them. They were then examined & stamped if passed. This proof was primarily for the gunmakers protection as it prevented a lot of work being done a faulty tube. More tubes failed proof I believe in this provisional proof than in the later Definitive proof.
