Well, you can bet that the light loads will have the bases marked with blue (cool) marker so there is no mistake! As to the loading, I do it for a living so tailoring loads is no big deal. I just know that the GMX loads might be a little much for a deer sized animal. Of course if that is what is in the chamber when an animal presents itself that won't slow me down for a second!
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But co the more I hear about bushbuck the more I reconsider the load to use on them. And the 25 year old 300 Win Mag is staying home, I don't want to chance it getting lost.
So much of this stuff is all about us nerds exercising our nerdness to upteenth degree...so what makes ultimate sense to one of us is totally missing the point for another.
Me? If I wanted to take your list of critters with my 375 I'd just load up the 250gr GMX or TTSX to about 2,700 (give or take 50 to find the accuracy node) and never look back.
But I tend to be a minimalist.
And I am stupid, so I have to follow the KISS rule!
For instance...I am currently in the early, early stages of thinking about a Buff hunt. I will use a 416 Rigby. I will likely also want to take a few other critters. I will shoot them all with the same load.
I really don't want to mess with hauling two rifles, and I cannot imagine how bad it might be to goof up and have a 350gr Speer up the pipe instead of the 400gr TSX or 450gr Woodleigh when I drop the hammer on a buffalo.
Oh, and your GMX loads won't be too much...and if you are really concerned, just bring that 300!
Regarding the time to change ammo, I only know this...I always carried earplugs with me on my hunt. In 15 animals, I did not get the plugs in for one! Stuff always seemed to happen pretty fast, and I was always focused like a laser on getting in position, getting on the animal, etc. No time to mess with plugs. I would not want to be messing with changing ammo when stuff is going down.
But then, I am old, slow and stupid...so take what I say with a grain of salt.
Regarding your ammo loading...I also had an Amm0 Manufacturer's License (along with an FFL) back in the 80's. Did it mostly to get stuff at wholesale and to help friends out. Do you do it full-time, or on the side?
Have fun counting the days! Unfortunately, it will be over before you know it...so savor every minute!
Tim