I think it's pretty common knowledge that the ogive on 2 bullets of the same weight and caliber, but different manufacturers differ, so seating to equal overall lengths from the base of the case to the tip of the bullet is not the most exact way to look for accuracy. I have also had the experience where the ogive position changed in a new box of 150gr Hornady SP .270 bullets compared to a previous box I had on hand. I caught it because the cannelure was in a different position.
Anyway, the current thought came about when I shot my 6.5 Creedmoor with Sierra 140gr SBT and Hornady 140gr SP, both loaded with 40gr of H4350 and seated at 0.015" from the leade.
Both 5-shot groups at 100 yards were less than 1 inch, but the Sierras landed 0.6" above my point of aim while the Hornady bullets landed 1.5" high.
I measured each bullet with a comparator to see what the difference was in the position of the ogive:
Sierra OAL base to tip = 1.258" Base to ogive = 0.779" Therefore, tip to ogive is 0.479"
Hornady OAL base to tip = 1.252" Base to ogive = 0.734"; tip to ogive = 0.518"
On this basis, the Hornady bullet has 59%, while the Sierra bullet has 62%, of their respective weights behind the ogive.
Would that be enough to explain the difference in the point of impact?
Anyway, the current thought came about when I shot my 6.5 Creedmoor with Sierra 140gr SBT and Hornady 140gr SP, both loaded with 40gr of H4350 and seated at 0.015" from the leade.
Both 5-shot groups at 100 yards were less than 1 inch, but the Sierras landed 0.6" above my point of aim while the Hornady bullets landed 1.5" high.
I measured each bullet with a comparator to see what the difference was in the position of the ogive:
Sierra OAL base to tip = 1.258" Base to ogive = 0.779" Therefore, tip to ogive is 0.479"
Hornady OAL base to tip = 1.252" Base to ogive = 0.734"; tip to ogive = 0.518"
On this basis, the Hornady bullet has 59%, while the Sierra bullet has 62%, of their respective weights behind the ogive.
Would that be enough to explain the difference in the point of impact?