This may be a stupid question and maybe I'm overthinking it. I understand that there is all kinds of ways to zero  eg: 25 yard zero, 50-200 yard zero, 100 yard zero,  etc... Not really discussing which way is best but more about determining how to measure tha actual distance. Is the distance determined from the end of the barrel or is it from the shooters position. I do realize this is only a difference of maybe a foot or two depending on barrel length such as a handgun or a rifle. I'm guessing that it is probably not a big deal but was just curious.

Not going to matter

Exterior ballistics begin when the bullet exits the barrel.

Muzzle crown.

It's not going to matter unless you plan to shoot the exact same ammo every time. Even differences in ammo will change your POI at distance.

Yes, but even round to round variance of match grade ammo will make up for muzzle vs end of bench.

Perhaps OP is forgetting about the length of the bullet.  A longer bullet which is seated further out in the case creating a greater overall length will be closer to the target than a round of a shorter overall length.

Based on the responses, I was obviously overthinking this and wont worry about it. Thank you for the replies...

Neither.  It doesn't matter.  It's not that much of an exact science.

Your rifle / load / environmental combination is going to determine that.  If you really want to know where your rifle shoots to the gnat's ass, you have to shoot it at varying ranges and conditions, record it all, and get enough data to make that determination.  If you're splitting hairs, using data off of a box or the manufacturer's website isn't going to be 100% accurate.

Just do it from the shooter's position.  Yes, exterior ballistics start as the bullet exits the muzzle, but you'll probably never be able to tell the difference which you choose to reference.

Yes, you're overthinking it.

Interesting question, but I think not really significant. Don't forget about wind variances, air temperature changes, and the rotation of the earth.

Zeroing to an artificial, standard distance will produce more uncertainty and error than will the difference between measuring from your face to the target vs. muzzle to the target.

FLAME SUIT ACTIVATED.