profile before the test shows that the effect of firing soft iron shot was to deform the gun barrel so that the choke taper ras shifted toward the muzzle. After the test, there was a bulge on the outside surface of the barrel, shown in comparisor to the longitudinal profile of the outside diameter before the test in Fig. 7(b). Deformation of the barrel had been detected after the first 100 rounds of iron-shot ammunition had been fired, and the bulge grew progressively larger as the test ontinued Apparently, the bore of the failed barrel was not concentric with the outside surface, because the wall thickness at a given distance from the breech varied widely among different points around the circumference. For example, at a distance of 5 mm(0. 2 in. )from the muzzle, the wall thickness varied from 1. 3 to 2 mm(0.051 to 0.080 in The microstructure of the barrel material was a mixture of ferrite and coarse pearlite. The alloy had a hardness of 163 to 198 HB(converted from Vickers hardness measurements) Based on previous tests, in which the hoop stress in shotgun barrels had been measured when lead-shot ammunition was fired, the safety factor had been estimated at 2.0. In this instance, it was concluded that wall thickness variations reduced the safety factor to about 1.3 for lead-shot ammunition. Previous tests had also shown that lead shot deformed extensively by impact with the bore in the choke zone of this type of gun barrel Analysis. The major stresses in the choke zone are produced by impact of shot pellets against the bore. When lead shot is used, the lead absorbs a considerable amount of the impact energy as it deforms. Soft iron shot, on the other hand, is much harder than lead and does not deform significantly. More of the impact energy is absorbed by the barrel when iron shot is used, producing higher stresses In this instance, had the gun barrel been of more uniform wall thickness around its circumference, it might not have deformed. However. it was believed that conversion to iron-shot ammunition would increase stresses in the barrel enough to warrant an increase in the strength of this type of barrel Conclusions. The shotgun barrel deformed because a change to iron-shot ammunition increased stresses in the choke zone of the barrel. Bulging was enhanced by a lack of uniformity in wall thickness Recommendations. Three alternative solutions to this problem were proposed, all involving changes in specifications The barrel could be made of steel with a higher yield strength The barrel could be made with a greater and more uniform wall thickne An alternative nontoxic metal shot with a hardness of about 30 to 40 HB could be developed for use in the ammunition Analysis of Distortion and Deformation Revised by Roch J. Shipley and David A Moore, Packer Engineering and william Dobson, Binary Engineering Associates, Inc. Failure to Meet specifications Parts sometimes do not perform to expectations because the material or processing does not conform to requirements, leaving the part with insufficient strength. For instance, a part can be damaged by decarburization, as discussed here for a spiral power spring Figure 8 shows two spiral power springs that were designed to counterbalance a textile- machine beam. The spring at left in Fig. 8 was satisfactory and took a normal set when loaded to solid deflection in a presetting operation. The spring at right in Fig. 8, after having been intentionally overstressed in the same manner as the satisfactory spring, exhibited 15% less reaction force than was required at 180 angular deflection because it had taken a set that was 30 in excess of the normal setprofile before the test shows that the effect of firing soft iron shot was to deform the gun barrel so that the choke taper was shifted toward the muzzle. After the test, there was a bulge on the outside surface of the barrel, shown in comparison to the longitudinal profile of the outside diameter before the test in Fig. 7(b). Deformation of the barrel had been detected after the first 100 rounds of iron-shot ammunition had been fired, and the bulge grew progressively larger as the test continued. Apparently, the bore of the failed barrel was not concentric with the outside surface, because the wall thickness at a given distance from the breech varied widely among different points around the circumference. For example, at a distance of 5 mm (0.2 in.) from the muzzle, the wall thickness varied from 1.3 to 2 mm (0.051 to 0.080 in.). The microstructure of the barrel material was a mixture of ferrite and coarse pearlite. The alloy had a hardness of 163 to 198 HB (converted from Vickers hardness measurements). Based on previous tests, in which the hoop stress in shotgun barrels had been measured when lead-shot ammunition was fired, the safety factor had been estimated at 2.0. In this instance, it was concluded that wall thickness variations had reduced the safety factor to about 1.3 for lead-shot ammunition. Previous tests had also shown that lead shot was deformed extensively by impact with the bore in the choke zone of this type of gun barrel. Analysis. The major stresses in the choke zone are produced by impact of shot pellets against the bore. When lead shot is used, the lead absorbs a considerable amount of the impact energy as it deforms. Soft iron shot, on the other hand, is much harder than lead and does not deform significantly. More of the impact energy is absorbed by the barrel when iron shot is used, producing higher stresses. In this instance, had the gun barrel been of more uniform wall thickness around its circumference, it might not have deformed. However, it was believed that conversion to iron-shot ammunition would increase stresses in the barrel enough to warrant an increase in the strength of this type of barrel. Conclusions. The shotgun barrel deformed because a change to iron-shot ammunition increased stresses in the choke zone of the barrel. Bulging was enhanced by a lack of uniformity in wall thickness. Recommendations. Three alternative solutions to this problem were proposed, all involving changes in specifications: · The barrel could be made of steel with a higher yield strength. · The barrel could be made with a greater and more uniform wall thickness. · An alternative nontoxic metal shot with a hardness of about 30 to 40 HB could be developed for use in the ammunition. Analysis of Distortion and Deformation Revised by Roch J. Shipley and David A. Moore, Packer Engineering and William Dobson, Binary Engineering Associates, Inc. Failure to Meet Specifications Parts sometimes do not perform to expectations because the material or processing does not conform to requirements, leaving the part with insufficient strength. For instance, a part can be damaged by decarburization, as discussed here for a spiral power spring. Figure 8 shows two spiral power springs that were designed to counterbalance a textile-machine beam. The spring at left in Fig. 8 was satisfactory and took a normal set when loaded to solid deflection in a presetting operation. The spring at right in Fig. 8, after having been intentionally overstressed in the same manner as the satisfactory spring, exhibited 15% less reaction force than was required at 180° angular deflection because it had taken a set that was 30° in excess of the normal set