That all sounds correct and good to me. First, you gotta understand different bullets are contoured differently so that the tip can extend the bullet deeper into the chamber before the side of the bullet ever touch the grooves. For those bullets, the OAL will be longer than it would be for a short, fat, stubby bullet that does not have a tip that extends much further in front of where the bullet hits the lands. Also, the only point to the whole concept of OAL is whether the cartridge will fit in a magazine. It has nothing to do with how it will function once you get it into the action or chamber it. If you never use your magazine, you would have no reason whatsoever to measure OAL. What you will want to measure is the length from the base of the cartridge to the OGIVE of the bullet. The ogive is the front-most part of the bullet that will first touch the lands of the barrel if allowed to do so. That is also the part of the bullet you should be measuring from to determine accurate seating depth anyhow, because tips can be deformed and give you a false or inaccurate indication of the bullet's seating depth anyhow. There are tools for measuring from the ogive, any serious handloader will use them, and should be able to tell what they're called, but I can't seem to do so at the moment! :)