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Originally Posted by Bart B
. . . what's the "inch/Degree actual/theoretical" numbers for?
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Bart, that's the number of inches added to group diameter at 100 yards by each degree of bullet tilt. Vaughn's bullet was tilting 0.22 degrees when it was tipped 0.0035" off-axis (0.007" total indicated runout). The M72 was tilting 0.175° tipped 0.004" (0.008" TIR) off axis. It seems like right around 0.2 degrees is about as much tilt as matters. Beyond that, the bore seems to straighten any additional tilt out.
I should probably have translated the inches to moa, but just was running by the available data, which was in inches from Vaughn. It's in moa from Abbatiello, but I converted it for consistency. (At least, I think I did. I should reread and check that).
The theoretical number is what Vaughn's calculations showed you would get if the gun didn't straighten the bullet any in the bore, IIRC.
No question about the shoulder determinant. IRRC, Hatcher actually measured up to -0.006" shoulder setback from rapid chambering of the .30-06. Of course, the heavier the finished cartridge, the more momentum it has.
I use a device I made to measure from the shoulder to the bullet ogive of a cartridge. It gives the best consistency. I understand the Redding Instant Indicator will do this, too, as well as make several measurements mine won't. On the other hand, mine is caliber convertible. Just change the knurled shoulder profile nut on the bottom and the ogive riding plunger above it. Both those parts I use my actual chamber reamer to make. I can also use it to make the measurement on the Stoney Point (LNL) Overall length comparator, set the zero there, then read the number of thousandths off the lands directly on the dial. But if they are chambering hard enough to set shoulders back, the only thing I can think to do is chamber a bunch and extract them unfired for measuring until you learn how much average allowance to make for them with your components in your gun.
