I ordered a 5/16-36 tap to make a DIY case to go with my Stoney Creek Overall Length Gauge since Hornady, who took that product over, doesn't sell one for the 30 RAR. The tap is good for more than one case, so if anyone wants me to make one for them, send me a clean, resized case and return postage. If interested, contact me for my address. The tap should be here next week.
For typical tangent ogive bullets like we will be seeing, it may take a long one to reach to the lands without falling out of the case. Probably going to need a 168-180gr 30 cal bullet to measure it. There's an old trick to establish the absolute leade length. Turn a flat base bullet around backwards and measure where it stops at the lands. That will show the absolute leade length since the flat base it precisely at the diameter where the ogive ends. The impact it has upon a spitzer or round nose COL will not be reflected by the absolute distance unless you will be loading wad cutters however. IIRC and I may not, my original 450b barrel had something like a .32 absolute leade, which is a little "roomy". Then again, the entire chamber was "roomy". I could actually load 300gr Hornady XTP Mag bullets to the lands without exceeding 2.26 COL since it is so blunt on the end. Since you're more concerned with how a particular bullet measures, the absolute lead is just an esoteric measurement. It would be interesting to see what different leades are out there for the 450b since there are a lot more barrel makers since back when I measured my original Bushmaster barrel. I do recall measuring a Trident barrel and it was spot on with the
SAAMI spec.
Hoot