If fine and quick-burning powder be used in a long barrel, the powder is flashed into propelling gas, instantaneously, and beyond a certain length of barrel has no further expansive power, and the result is a friction of the charge in escaping, that affects the shot and consequently the pattern on the target. If slow burning powder be employed in a short barrel, the whole of the powder cannot be so instantly flashed into the propelling gas and some portion of it is, as a result, driven unconsumed from the muzzle of the gun. This fact can be very readily ascertained by firing a gun over a bed of clean snow or over a spread of white cloth. The unconsumed grains can be readily seen on the white ground. If a less charge be used in order to consume all the powder, less velocity will be given to the projected charge, and weak shooting and a poor, scattering effect on the target is the consequence. _Proof of Barrels._—In consequence of the bursting of guns of an inferior quality, all barrels of English manufacture that are intended for home use, and also those designed for exportation, except a certain class of arms, are required by law to be proved and stamped with the proof-mark and also what is termed a view mark, which is a stamp or impress of the inspection after the barrels were grooved. There are two of these proofs called, respectively, the London and the Birmingham proof. In 1855, an Act was passed by the English Parliament, called, “The Gun Barrel Proof Act,” which enacted that all barrels should be proved, first, in the rough, and was called the provisional proof, and afterward when the barrels were put together, breeched and percussioned they were proved again, and this was called the definitive proof. The arms to be proved are to be divided into classes, and the first class comprises single-barrelled military arms of smooth bore, and they are not qualified for proof until they are fitted and complete to be set up or assembled. The second class comprises double-barrelled military arms of smooth bore and rifled arms of every description, whether of one or more barrels, and constructed of plain or twisted iron. The fourth class comprises double-barrelled guns for firing small shot, and these are subject to the two proofs, provisional and definitive. For provisional proof, if of plain metal, the barrels are to be bored and ground to size, the vent hole drilled of a size not exceeding one-sixteenth of an inch diameter, and a vent enlarged to one-tenth disqualified it for proof. Notches in the plugs, instead of drilled vents, also disqualified them. If the arms are of twisted metal, they are to be fine bored and struck up, with proving plugs attached, and vents drilled the same as in plain barrels.