A friend gave me a handful of 407 grain bullets from a Magma mould which measured 1.005" in length. I also acquired a few 405 grain LaserCast bullets that measured 1.047" in length.
Using the Greenhill formula, the twist required to stabilize those bullets is 31.44 and 30.18 respectively. That means the Magma bullets would have a higher chance of stabilizing than the LaserCast.
The target on the right was shot with the Magma bullet, and the target on the left has one hole at 12:00 on the edge of the paper from the LaserCast bullet. (I shot 3 shots with a 370 grain bullet at the same target, which accounts for the other holes and notes on the lower part of the target.) I shot 3 times at the left target with the 405 grain bullet and only found two of the holes. The one at 12:00 and one that was about 14" to the left at 9:00. Both were noticably keyholed. The moral to this story is that it is the length of the bullet that determines bullet stability, not weight, just as the Greenhill formula predicts.
The other thing I was trying to get a handle on was the lack of consistent performance of the 370 grain bullets using 30 grains of 5744 and TP filler. I thought I'd bump the load up a grain to 31 grains just to see what would happen.
The left target above and the right target in the picture below demonstrate the poor performance of the 30 grain load. The left target below shows the results of the 31 grain load. The first three shots were 1.75 inches apart. I shot another target and went back to this one with two additional shots. The cloudcover was darker then and I didn't have as good a sight picture as I did when I shot the first three. I was flat amazed at the change in the accuracy by adding just one grain of powder! This might not be a big AHA! moment for some of you that have been reloading for years, but for me, being new at this, it was quite a revelation.
