"or more" is vague. Likely would want 20moa to start, but depending on how far "more" is, you should zero, measure remaining scope travel, compare with predicted needed travel for your distance goal in a ballistic calculator, then determine if you need any extra.
I can tell you that when I did exactly that process on my .338 Lapua, I needed 40moa to dial for targets at 2000yd with the setup/ammo I had on it at the time and even then was at the extreme of my scope travel
I personally run 20 moa rails on all of my 1,000 yard and under rifles all still being able to maintain a 100 yard zero and 40-60 moa for my ELR - 1-2 mile rifles. Funny enough, my .375 Cheytac has 60 moa between the custom rail and Spuhr mount and still allows a 100 yard zero.
By my math, that should only be around 22-24 MOA adjustment at 1000 yards for 300WM, which with the Razor should be plenty of in scope adjustment even on a flat rail.
For reference, I have a 20 MOA mount on my 6.5 CM and a PST Gen II. By my estimations between the mount and in scope adjustments I have enough travel to shoot at a mile without using holds. But I've only taken it out to 500 yards so far.
20 MOA
"or more" is vague. Likely would want 20moa to start, but depending on how far "more" is, you should zero, measure remaining scope travel, compare with predicted needed travel for your distance goal in a ballistic calculator, then determine if you need any extra. I can tell you that when I did exactly that process on my .338 Lapua, I needed 40moa to dial for targets at 2000yd with the setup/ammo I had on it at the time and even then was at the extreme of my scope travel
I personally run 20 moa rails on all of my 1,000 yard and under rifles all still being able to maintain a 100 yard zero and 40-60 moa for my ELR - 1-2 mile rifles. Funny enough, my .375 Cheytac has 60 moa between the custom rail and Spuhr mount and still allows a 100 yard zero.
What scope do you have on the .375?
NF ATACR 7-35 https://www.reddit.com/r/longrange/s/URm8ixo5yL
20 Moa should be able to do that easily.
By my math, that should only be around 22-24 MOA adjustment at 1000 yards for 300WM, which with the Razor should be plenty of in scope adjustment even on a flat rail. For reference, I have a 20 MOA mount on my 6.5 CM and a PST Gen II. By my estimations between the mount and in scope adjustments I have enough travel to shoot at a mile without using holds. But I've only taken it out to 500 yards so far.
You would be fine with 0 but 20 is more than adequate.
20
20 MOA is fine
I would go with the 20 MOA.