Fascinating! Back in the early 80's I had a friend that was on the Honor Guard at the air base. He said they were having lots of trouble with their M1's so I went down to see if I could help. The rifles would fire the first & second rounds fine, then the bolt would close on an empty chamber. Bang, Bang, Click doesn't go over very well at a funeral detail! Some of the guys would go through the motions but not fire on the second volley so there was a good chance of some rifles firing on the third.
Through some shade tree testing, I figured out that the bolt was bouncing and closing faster then the follower arm could push the next round up. As the clip empties, the follower arm rotates up and reduced the tension on the op rod spring. When I drilled out the BFA to 3/16" (.187") the rifles would rip off all eight rounds as fast as you could pull the trigger. The M1's started behaving and they had no further problems.
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