I cut this up a bit to fit how my mind processed the subject matter - even though it’s a little backwards of how you asked:
I was fascinated by the observation that powder charge isn't the driver here. It seems that many start with bullet jump and then fine tune the powder once the best bullet jump has been determined. Talk about flipping load development on its head!
There’s a PRB article flipping a lot of us on our heads right now. For my 25yrs of reloading, I have been taught, have observed, and have subsequently taught others that “charge weight is the big knob, and seating depth is a small knob.” This new info seems to flip that.
I have read the article, but haven’t reconciled it fully yet against my own experiences - admittedly, that is a hot topic for my reading and research interest, following the current book I’m reading. Maybe a year from now I will say the opposite, but personally, I don’t expect it to be so - Far too many times tweaking both of these to believe the roles and ranks will magically change after reading the article and retesting the hypothesis myself. But - I love learning and proving old paradigms invalid, so I’m excited to recreate and stress test the article’s proposals.
But is bullet seating at .040" increments essentially changing the bullet barrel time enough to affect precision.
Chris Long’s OBT is one that I’ve really struggled with, for many reasons. His science appears sound, but I simply haven’t observed it to hold true - I can develop a load in a long barrel and have it remain forgiving in a shorter barrel, even a specialty pistol. Adding suppressors also influences barrel time, throat erosion does as well... temperature variations, powder lot variations... if we’re talking about a very specific barrel time, then I shouldn’t see the results I see.
I would go as far to say I believe far more in a forgiving charge weight window (not necessarily claiming Dan Newberry as champion here, so don’t misinterpret my statement here) than I do in an optimal barrel time. We might be able to intuit a tangible link between bullet dwell time and the natural Barrel harmonic, but I’m not convinced. So I will rarely ever say “velocity node,” as I’m not convinced the velocity is the driving influence. As a specific example of a counterargument to OBT or velocity nodes; I’ve shared here frequently my disappointment with a Rock Creek barrel two years ago which I would say failed very young. I lost over 100fps before 700 rounds, and lost ~15fps per 100rnds until 1,000rnds and then ~35fps from 1100-1400. Do that math, I was a few hundred feet per second slower at the end than the beginning. I did Satterlee, OCW, and Audette Ladders repeatedly in its life, and my powder charge nodes didn’t move. The correlation between powder and speed slowed down, but the flat spots in the Satterlee curve appeared at the same charge weights, and I saw the same clustering in 600yrd Ladders. I even added over a grain more powder, jumping up a node, and was still slower than when the barrel was new - so why did a charge weight node persist through dramatically changing barrel time and dramatically changing velocity? A touch over 3000fps fell to low 2700’s, and the charge weight node never changed. If OBT is the critical knob, it certainly doesn’t explain that experience. Equally, I’ve taken far too many loads across dramatic barrel length changes - you might recognize a 10.5” barrel has a different barrel time than an 18”, or a 14” barrel different than a 24”. But the node sustains... If OBT is the knob, how is that possible?
@Varminterror, is there a consensus on how bullet jump affects accuracy/precision. I'd read many years ago that seating the bullet near the lands increases the chance of properly aligning the bullet to the bore.
So back on point here - There doesn’t seem to remain a consensus, not any longer at least. We all were told secant ogive bullets with flat bases and long bearing surfaces have been the standard of short-range precision (aka, raw precision) for generations. Why? Because the bullets enter the leade consistently, grip the barrel consistently, and establish pressure consistently. Everything we do to bullets to make them more aerodynamic or more forgiving tends to hurt this raw precision - boat tails and tangent ogives, short bearing surfaces, etc. So we’ve chased that standard and tried to discover more and more ways to make the penalty lighter. We might really be there today, such we know how to make ammo and bullets and barrels sufficiently forgiving to close the gap... I can’t say. But I know I can’t claim to shoot small enough to tell the difference, undeniably, that any particular design or load method - including jump - makes an absolutely definitive step change. Not to say it doesn’t matter, but to say I am never surprised to hear someone say they are loading a bullet to a very different jump than I do, and getting the same results.
So I’m resigned to enjoy reading it all, but believing my own eyes when I run through data on my own bench. If I can replicate data easily and definitively, I believe it is definitive. When I can’t, well, I don’t find it sufficiently definitive to totally upturn my apple carts.