Mikecr
Well-Known Member
With 3thou interference fit(excess) and FL sizing(way excess) of necks, you likely have huge neck tension.
So much so that it's directly affecting your powder burn curve(not normal while OTL).
By 'burn curve' I'm not talking about MV, but of powder burn behavior & timing.
Best bullet seating CBTO is normally independent of powder. It's a coarse prerequisite to accuracy that is not part of tune.
Powder is tune, and it's a fine adjustment. Neck tension(length of neck sizing) normally has a fine affect to tune. This is with partial neck sizing to provide spring back grip against .xxx" of seated bearing.
But with FL sizing of necks, you throw tension adjustment into an extreme, not only in affect to a burn curve, but to variance in it. This because any sized/unexpanded neck beyond bullet bearing, binds against the bearing-base junction.
This is why I would never FL size necks to begin, and also why we should not adjust seating so much AFTER powder tune.. Seating, full testing of it, should be completed before moving to powder testing. Then, tweaking of seating, no more than ~10thou of full tested, will shape grouping further.
See, if you were doing normal partial neck sizing, with normal 1thou interference, you could do full seating testing, even with tune, while having way less affect to tune(so that you can easily identify best seating, instead of having a collapsing tune on top of results). But it's still better to completely clear yourself of coming in & out of a tune while trying to determine best seating.
