automatic gun of this size is, on account of its heavy mean recoil, an altogether workable proposition. The Vickers automatic 37-mm., for example, is made in two weights; one of these throws a 1 lb, shell at 1,800 foot-seconds at 300 rounds per minute, at which speed of discharge the recoil reaction would be about 300 lb. The weight of this gun is given as 3¾ cwt. This gun is quite unsuited to aeroplane service, both from the point of view of recoil and weight; there is, however, a lighter type by the same firm, of the same calibre, semi-automatic, throwing a 1½ lb, projectile with a velocity of 1,200 ft, per second, the weight of the gun being given as 110 lb. Presumably the maximum rate of fire of this gun would be about thirty rounds per minute, or the weight of metal thrown per minute, 45 lb. This is about 2½ times the weight per minute given above for the machine-gun.
§ 52. Weight per minute as limited by Recoil. Quite apart from mechanical details, however, a real limiting factor exists in the recoil reaction to the momentum per second permissible, and this limit may be taken as applying whatever the type of gun may be; consequently, since the muzzle velocity of one type and another is not widely different, the weight discharged per second or per minute will have an approximate maximum for any particular aeroplane no matter what the type of gun may be. This is the reason why it is possible and, in the author's opinion, advantageous to employ duplication, or even fit three or four barrels in the case of the machine-gun; whereas an automatic 1-pounder under like conditions could not reasonably be allowed to fire at over 60 or 80 rounds per minute.
§ 53. Present Advantage of Machine Guns. Future Possibilities discussed. At present there are very few cases in which the automatic or semi-automatic 1-pounder could compete with the machine-gun as an aeroplane arm.
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