I looked into it a little bit and it seems Bryan Litz noticed this too (see below). Apparently there are two different versions of the bullet. One is a bit longer than the other. I checked and all the factory ammo I have from the past year has the less opaque ballistic tip (which is the bullet that shot much better for me).
I would note that something similar happened to me with the 140 grain ELD-M bullets. They shot great and then when I bought a new box they sucked. I would guess there is something similar going on. At the time I didn't pay much attention to it and didn't notice/check if there was a difference in the ballistic tips or the dimensions between those that shot well and the ones that didn't.
Anyway, I have no idea how to know which version I am getting when I buy a box of bullets. I guess I'll have to do some load development and switch to a different manufacturer.
There appears to be two different versions of the Hornady .264 caliber 147 grain ELDM. One is a longer nose, lower drag, higher (but less consistent) BC, while the other is a shorter, higher drag,...
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