Measurements of Fluid Friction Loss in 0.50 Caliber Rifled and Unrifled Gun Barrels

Abstract

The High Speed Water Tunnel is operated by the California Institute of Technology under Contract OEMsr-207 with the OSRD and is sponsored by Division 6, section 6.1 of the NDRC. The tests reported in this memorandum were made at the request of Division One of the NDRC of the OSRD. The report covers measurements of the fluid friction loss in two 0.50 caliber gun barrels, one rifled and the other unrifled, and compares the results with the friction loss through hydraulically smooth tubes. The conclusions may be summarized as follows: 1. Within a margin of approximately 7% the loss in both gun barrels, for identical rates of flow, is the same as that for a hydraulically smooth tube of 0.500" diameter in the Reynolds number range of 0.5 x 10^5 to 1.5 x 10^5 covered by the tests (See Figure 4). 2. The 7% margin represents the spread between the losses for the two barrels as follows: (a) The loss in the unrifled barrel is 4% more than for a hydraulically smooth tube due to its greater roughness. ( b ) The loss in the rifled barrel is 3% less than the loss in a 0.500" diameter smooth tube due to its greater effective cross-section, and consequently lower average velocity of flow. 3. An examination of typical trends of the friction factor at higher Reynolds numbers indicates that values of "f" can probably be extrapolated parallel to the curve for smooth tubes shown in Figure 6.