MarkCO and Metal god,
This illustrates what Bart and I are saying:
Note that if the case were shorter because of greater shoulder setback, but the neck was the same length (trimmed in a shoulder-registering trimmer), and the bullet seating depth into the mouth was the same, though there would be a larger head clearance between the breech and head, the bullet jump would be unchanged. This is what Bart and I are talking about. If you keep that Shoulder-to-Ogive throat contact diameter distance the same, bullet jump stays the same. Neither Bart nor I are addressing how you load ammunition to hold that distance constant. We are just stating what the principle involved is.
I have generally found that because seating dies contact the bullet ogive further up from the part of it that contacts the throat, where the OP was finding ogive variation, my gauge can find a couple or three-thousandths of variation in shoulder-to-ogive length even when case head-to-shoulder distance is perfectly consistent. I use my gauge to sort my loaded rounds on the assumption matching that distance helps match the bullet profiles. I've never done any rigorous study of the practical effect on accuracy at long range, but my expectation is that will provide a closer BC match between bullets.
Metal God,
As I said, I can't recall my source. I'll have to run the experiment for myself. I have the feeling it was new brass, so there may have been a softer shoulder than reloaded brass and it may have had a bigger runup into the chamber shoulder, letting it gain a little more inertia. It may have been done with magnum primers, too.
This illustrates what Bart and I are saying:
Note that if the case were shorter because of greater shoulder setback, but the neck was the same length (trimmed in a shoulder-registering trimmer), and the bullet seating depth into the mouth was the same, though there would be a larger head clearance between the breech and head, the bullet jump would be unchanged. This is what Bart and I are talking about. If you keep that Shoulder-to-Ogive throat contact diameter distance the same, bullet jump stays the same. Neither Bart nor I are addressing how you load ammunition to hold that distance constant. We are just stating what the principle involved is.
I have generally found that because seating dies contact the bullet ogive further up from the part of it that contacts the throat, where the OP was finding ogive variation, my gauge can find a couple or three-thousandths of variation in shoulder-to-ogive length even when case head-to-shoulder distance is perfectly consistent. I use my gauge to sort my loaded rounds on the assumption matching that distance helps match the bullet profiles. I've never done any rigorous study of the practical effect on accuracy at long range, but my expectation is that will provide a closer BC match between bullets.
Metal God,
As I said, I can't recall my source. I'll have to run the experiment for myself. I have the feeling it was new brass, so there may have been a softer shoulder than reloaded brass and it may have had a bigger runup into the chamber shoulder, letting it gain a little more inertia. It may have been done with magnum primers, too.