Sounds like you have nice country there in Iowa. And I, for one commend you for using a 375Ruger, even if it was pushed by law. I've used lots of large calibers in Africa on smaller game, so 375Ruger for whitetail sounds reasonable. We have a 375 Ruger in Africa, and I will share its loads.
Ruger Hawkeye rifle, 375Ruger, 250gn Barnes TTSX, Hornady cases (2xx fired), Rem9.5M primer, 84.0gn Rel17. Crimped with Lee Crimp die.
This produces approximately 2825fps, by Chronograph. I will try to attach/insert a jpg of a 100-yard group:
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But I've also done some more recent work with another rifle.
A few years ago I picked up another 375Ruger, this time a Mossberg Patriot, in the US for load development and practice. And I wanted to try a rifle company that I had never used. The rifle was decent and would be good for hunting (3/4" to 1.5" typical groups), except that the bore shows excess copper fouling and we have other rifles that outshoot this particular rifle, so it never goes on a hunt.
For loads, I particularly tested the Hammer Hunter 248 (weighs 244gn).
The newish Winchester Powder StaBall6.5 was used, along with WinLRM primers.
The Hammer Hunter worked well and allowed a lot of that StaBall6.5 powder to be used. 89grains produced around 2950fps (by chronograph). Attached are two pix of two shots each, same day, one seated 3.50" COL and the other at 3.60"COL. The bullet wants to be single fed.
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And below is the target for the 3.60" COL
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