I am attaching a paper reporting where we now stand in development and testing of a new monolithic copper ULD bullet design for ELR rifle shooting. I now see that practical accuracy is a limitation on how fast these bullets should be spinning out of the muzzle. I am changing my rifling twist recommendation from 20 to 24 calibers per turn; i.e., from 6.6 to 8.0 inches per turn for 338-caliber rifles for firing (any) copper bullets. That should reduce 5-shot group sizes from 0.75 to 0.50 MOA, which is probably good enough for most ELR shooting, without reducing bullet speed at extreme range too much. Initial gyroscopic stability (Sg) should be in the 2.0 to 2.5 range, instead of 2.5 to 3.0, for long copper ULD bullets. David Tubb has been kindly testing our 338-caliber prototypes at 1,000 yards.
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