wooden ammunition chest that carried 250 rounds. The early M1917 model had an angled corner and a leather strap handle on top. The later M1917A1 model had a square corner and a cloth strap handle on top. The wooden ammunition belt chest was replaced during WWII by the expendable metal box ammunition M1 adopted 6 May 1942. On 20 June 1945, a modified version known as the M1A1 was adopted. The M1A1 had a spring-loaded catch to fasten it to the M1917A1 tripod more securely and provide a better watertight seal. In the late-1940s the M19 box replaced the earlier metal M1 and M1A1 boxes, and a modified version known as the M19A1 appeared in the early-1950s and continues in use today. Variants US military variants M1917 The original gun suffered from a weakness related to the design of the receiver. Under field conditions, the bottom plates, which were dovetailed into the gun's two side plates, tore out. An early fix was to attach a roughly horseshoe-shaped steel bracket around the rearmost part of the receiver. A later fix was to rivet "stirrups" (right-angled steel pieces) to the bottom and side plates. The stirrup fix became the standard reinforcement until a more permanent fix for the problem was developed. Another reported problem was bulging in the side plates, which was probably caused by stresses put into the side plates when hammering the dovetails closed. The 1917 also had a simple sliding safety that blocked the trigger when moved to the far right position. These were removed as part of post-war refurbishment. M1917A1 In the 1930s, the Ordnance Department developed a new bottom plate, which had side flanges that came up on both sides of the receiver and were attached by rivets. This fixed the problem of the original bottom plates, and became standard for all M1917- and M1919-series machine guns. While the US Arsenal at Rock Island was the leader in converting the existing stocks of M1917-series guns over to 1917A1 configuration, other arsenals took part. In addition, the rear sights were updated for the new ammunition and were changed to yards from meters, and also did away with the World War I multiple-aperture disk on the rear sight. The top covers also had a stronger feed pawl pivot arm installed, so the gun could handle the stress of pulling an ammunition belt from the ground. Rock Island Arsenal also