You don't have a reason why you think these powder companies ( Hodgdon and Vihta Vuori ) are using different COAL's then what the bullet manufacture recommends when using there powders ???
I have a reason, though I have no idea if it's the actual reason, or not. Apologies for not also mentioning this in my earlier post.
Think of what COAL s are. They are a number for the overall loaded length of the round. They don't have to be the maximum allowable length, they can be just the length the round ended up being, when a specific bullet is seated to the desired depth. I think this may be where some of the confusion is coming from.
Break it down to basics, and look at the standards, vs different length numbers from this or that maker with certain specific bullets.
SAAMI COAL is the US standard, and is intended to provide a maximum allowable length that will work through the actions and barrels of all arms chambered in for that cartridge. It is based on the common bullet styles in use when the standards were created. It's meant to keep you off the lands, even if you load a full wadcutter to its stated length.
It is quite possible that bullets of unusual or uncommon profiles and lengths cannot be loaded to meet the listed max standard. It is also possible that certain bullets can be loaded to exceed the max listed length, and still be off the lands. The very long (for caliber) low drag bullets, and all copper bullets (which must be longer than lead for the same weight) are fairly recent developments. Most of the SAAMI standards pre-date the invention of these bullets.
Here's what is not being addressed when looking at the COAL alone, bullet seating depth. And, to a significant degree this matter MORE than COAL.
Take two bullets of the same weight, and the same base style (say flatbase), but different nose profiles, seat them to the exact same depth, and you can have two different COALs. Lets take .30 cal 150gr for example. Spitzer, and flat point/round nose. Same weight, different LENGTHs. Seat both to the base of the case neck, and you have the same seating depth, but different COALs. Change the spitzer flat base to a boattail, and you have yet another COAL when the base of the bullet is seated to the same depth as the others.
How far into the barrel the point of a bullet goes (the portion too small in diameter to contact the rifling) doesn't matter. How far into the case the base of the bullet goes can matter.
Maybe the different lengths listed from the different sources (other than SAAMI) are simply the length the round ended up being when the desired bullet was seated to their desired depth.
Maybe, that number ISN'T a requirement, its just reported because that's what they used.