Aug. 13, 1963 3,100,358 Aug. i3, 1963 T. R. ROBINSON, JR 3,100,358 RIFLED GUN BARREL Original Filled May 13, 1953 36 Sheets-Sheet 3 INVENTOR Ø?----- Ø? 02-4-T-T-T-T-T-Sh^ "GP2-4-4/2-26-7,5)ATTORNEY3 3, 99,358 United States Patent Office Patented Aug. 13, 1963 2 through the barrel by the firing of a propulsive charge, the 3,180,353 - . :: engagement of the helical lands with the material of the REFLED GUN BAERFREÄ, bullet imparts to the latter rotating motion necessary to Thomas R. Robinson, JSir, New Haven, Cezar, assignBF to The Marini Fireans Ciapany, Rew ?ayeKa, C63., a stabilize it in flight, and the function of the rifle is to im * corporation of Connecática i º i part to the projectile the minimum rotational velocity Contatioita of application a Ser. I No. 354,72, yay 13, necessary for this stabilization. As is understood, the only 1953. Tišs aplication Nov. 27, 1959, Ser. No. 856,331 portion of the rifling which significantly effects this "rota tion is one side or the driving side of each of the lands * 2 Cairns. (C. 42-78) - in the bore of the barrel, and it is the general experience This invention relates to rified gun barrels and more 0 that with 4 or 6 groove rifing, as is commonly" employed particularly to a barrel having a new, novel and advan in a .30 caliber rifle, the minimum depth of groove must tageous type of rifling, and to a method of effecting Stuch be approximately...004 in. to form a minimum driving land rifling, the barrel, so made possessing to a degree not side of .004 in. which is required for reliable engagement hitherto attained the attributes of low cost of manufac of the bullet by the land to impart the necessary spin to the ture, extreme accuracy of performance and long - useful bullet. Attempts to reduce manufacturing, costs by i de life. The present application is a continuation of my ap creasing the number of grooves or decreasing the depth plication, Serial No. 354,712, filed May 13, 1953, now of grooves to shorten the machining time, have resulted abandoned. : : : : : : : e in barrels which do not engage the projectile over a suffi In the manufacture of rifle barrels, the barrel is com cient area, and the result is a consequent failure to impart monly provided with a series of helical groovesicut in the 20) ; the necessary rotational velocity to the buillet. otherwise smooth wall of the bore of the barrei in order The effective driving area of the side of the lands work to give the projectilie a rotative motion or twist. These ing on a projectile may be roughly computed as the and : grooves - and the lands generated between them are ºgen side height multiplied by the length of the i engagement of erailly referred to as rifling. I Normally about four or six the land with the projectile and multiplied by the number of these grooves are provided in the bore, and they are | 25 of lands in the bore. Thus, if in a .30 caliber barrel we usually made by a cutting tool which is passed through the asSume a land engagement with the projectile for a bore of the barrel a number of times to complete the '' . ' length of 4% inch, the effective engaging area of all of the cutting of each, groove. : , . ' landis with the projectile will be .004 times 5.5 times the For example, a .30 caliber rifle may have from four to number of grooves (either 4 or 6) i provided in the barrel. six of such grooves which may be cut to a depth of .004 in. 30 it will be seein, therefore, that the area of "engagement in This means that the bore diameter of the barrelacross the , a .30 caliber firearm would be from:008 to .012 sq. inches lands between the grooves is 300 in., while the groove di depending upon whether 4 or. 6 grooves are provided. ameter across the bottoms of the grooves is .308 in., the It will also be seen that if the groove is made of a depth average being approximately. 304. in. The cutting tool i of .004 in. in a .30 caliber barrel, the groove depth will be which is passed through the barrel removes a small amount 35 approximately %5 or more of the bore diameter of the of this metal at each pass, the amount removed being ap barrel and the groove depth is always greater than Aioo proximately0005 in. This means that it would require of this diameter: " If it is attempted to reduce the depth i eight passes of the tool to make a cut of adepth of .004 of the grooye in order to shorten the manufacturing time in., and thus require eight passes for each of the grooves required to make the barrel below this figure, faulty en or 32 passes of the tool for a barrel having four rifiling 4) gagement of the rifling lands with the projectile results and grooves. This requires aº considerable length of time, a consequent failure to give the projectile the desired spin: in some instances up to 20 or 25 minutes, to cut the grooves Attempts to º counteract the reduction in the depth of the in oine barrel. groove by increasing the number of grooves to give more In some instances it has been, proposed to shorten the driving land sides also prevents any increase in efficiemcy in time required for providing the rifling ina barrel by the production because the total number of grooves must be use of a broaching tool having multiple cutting points 45 increased correspondingly to the reduction in depth. Fur which will form the groove with one pass of the tool. This thermore, with an increased number of grooves to be cut tool is provided with a number of circular lands of suc in a barrel, the mechanical requirements for production cessively larger size and appropriately notched to give equipment become so complex as to render the increase, in the groove-land width relationship, the lands between the 50 the number of grooves : cutia practical impossibility with notches being arranged behind each other helically upon existing machinery beyond relatively low - numbers of the broach with the appropriate helix angle required for grooves. " rifling. Such tools, although, giving more rapid machining According to the present, invention the grooves are time for a finished barrel, are prone i to shatter and are provided by a cold Swedging method in that a tool having costly to fabricate: aindi keep in condition for use. Fur helical ribs thereon is forced through the barrel, the tooli therminore, in Smaller bore guns, such as .22 andi.25 caliber, displacing the metal to form the grooves. The number of provision of adequate clearance for the metal removed in swedging ribs provided on the tool is the same as the the one or sometimes two broach passes makes for a weak number of rifingº grooves provided in the bore of :: the and generally unreliable tool. Furthermore, any one of finished barrel, and it is only necessary for this swedge the large number of individual cutting faces of the broach 60 or button to make one pass to complete the rifing opera may at any time dull and consequently scratch or - score tion so that the rifling time according to the present inven the groove in which the land is cutting. tion is 2 to 5 seconds per barrel as compared with the When bullets of appropriate size, which are approxi much longer time noted above in the usual Trifling mately the groove diameter of the barrel, are forced operation. - M 3,100,358 4 . In rifling a barrel by the swedging operation of the the grooves will preferably be substantiaily .0015 inch in present invention, I provide a much greater number of *** depth. It may also be noted that the front end 18 of the rifling grooves - that has heretofore been the practice and swedge member is tapered so, as to provide for its easy swedge these grooves to a much lesser depth. The number entrance into the bore of the barrel. · of grooves may, of course, vary, but I have found that 16 A very important feature, as may be noted from the of these comparatively minute grooves give good perform enlarged view of FIG. 4, is that the land sides í4 of the ance in the firearm having a barrel so made. Moreover, rifing grooves 12 are not in a radial plane passing through the depth of the grooves is approximately 1.0015 as com the axis of the bore, but are inclined or at an angle to pared with the grooves having a depth of .004 as - is the such a plane, and this angle is so chosen as to produce a i usual practice. The bore diameter is enlarged to maintain | 0 maximum effect on the bullet. It may be assumed that the same or greater effective cross section as compared the rifling is so directed as to effect a clockwise rotation with common practice. In other words, the barrel of a of the bullet, as seen in FIG. 4. .30 caliber gun according to the present invention would The radius of gyration of a solid body of generailly have a bore diameter across the lands between the grooves cylindrical shape mây be considered to be R/V2, where of .304 in. and a groove diameter across the bottoms of 5 R is the radius of the body.