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Concluding Remarks Gun tube erosion can set a limit to the development of more desirable weapons systems. Two things should be done if this limit is to be avoided. Research drawing on existing technology can provide materials better suited to withstand the severe mechanical, thermal, and chemical environment in a gun tube. Longer term, more basic studies can develop, at least empirically, pre- dictive models for the erosion process. The ability to predict offers the hope of being able to propose solutions. The Committee was impressed by the quality of the investigations con- ducted on the many facets of the gun tube erosion problem in the past. However, it appears obvious that the problem of defining the mechanism of erosion cuts across the missions of the various Army arsenals. It is therefore felt that future effort in this area would be more effective if a single leader and a single source of funding devoted exclusively to this technology area be designated. DESCRIPTION OF GUN SYSTEM The components of the gun system included in this report are primarily the gun barrel, the projectile and the propellant charge. Nomenclature is indicated in the first two figures. A gun barrel for fixed ammunition is shown in Figure 1. Rifling consists of helical grooves cut in the bore of the tube extending from the forcing cone to the muzzle end. The ridges between the grooves are known as lands. The forcing cone includes the origin of rifling where the grooves begin, and the commencement of rifling where the lands reach full height. Nomenclature for the various regions of projectiles and complete rounds of ammunition is given in Figure 2. In addition cannelures, partially visible under the grommet "O", are ringlike grooves cut in the rotating band in order to lessen the resistance offered to the rifling as the projectile begins to move along the
6 Chief Metallurgist, Triballoy Products of DuPont (302-453-2631), is a source of information on this material and its application. A key question on the use of any of these hard coatings is whether they would be effective in the gun tube in sprayed layers thin enough to be used without any finishing operations such as grind- ing or honing. 4. Wear-Resistant Inserts As has been noted, the use of wear resistant inserts is common in the engine field - cylinder liners, valve seats, etc., and in cutting tools. It is suggested that consideration be given to the use of a permanently installed wear-resistant insert at the origin of rifling. This would permit the continued use of the relatively soft bulk material needed in the tube for fatigue re- sistance, but provide a harder (at working temperature) mate- rial where it is needed for erosion resistance. Anchoring the insert firmly enough to resist the rotating force imposed by the projectile on the rifling might be handled by furnace brazing the insert into the gun tube during heat treat- ment of the tube. It is common practice in gear manufactur- ing to simultaneously furnace braze a pre-carburized insert into a gear and harden it while heat treating the bulk of the gear. Experimental inserts might be anchored in finished tubes by electron beam welding. Use of an insert opens up a whole new area for material selec- tion . . . including through-hardened steels, carburized and hardened (for compressive stress at surface) steel, die steels, high speed tool steels and others of good properties at high temperatures. Nitriding becomes feasible. 5. Cooling The drastic decrease in cutting tool life with increased temper- atures prompts investigation into means for reducing gun barrel temperatures. Cooling of the wear surfaces (i.e. the bore) might be accom- plished by a jet of expanding gas directed at the origin of rifling between rounds. Or, some cooling might be achieved by appropriate selection of a spray or wash which would also supply the insulating and/or lubricating function of Recom- mendation #1.
