Something doesn't add up. What you are saying is that a 325 WSM has 40lbs of recoil and a 338 WM has only 30. How exactly does a 325 generate a third more recoil than a 338?
Recoil numbers are only rough approximations, until you specify the load used and the weight of the rifle.
And, even the precise energy numbers only give you a rough idea of what the recoil will feel like. Stock fit to you, and stock design change what recoil feels like.
Cherry pick the loads and the rifles and you can get numbers that while accurate, don't seem to add up. Shoot a 200gr bullet at 2800fps in a .30, .32, or .338 caliber and your raw energy numbers will be the same.
Now, factor in the rifle and it can change, depending on the rifles used.
shoot that .338 from a 9lb rifle, and the .325 from a 7lb rifle and you will get different recoil numbers.
I don't have a .325 WSM, not going to get one, no interest. Learned my lesson on other "proprietary" cartridges. Like the .350 Rem Mag...
My advice is that if you are getting a .325WSM (or already have one) go out (or order in) and buy a closet full of factory ammo. Enough to last your shooting needs for the rest of your life isn't unreasonable. Now, today, while its still "hanging on" and before it becomes virtual "unobtainium".
Forget the cost. That's a one time expense. And cheaper than it will be when the round is dropped by the ammo maker.
.325 WSM is a niche round. Nor is it alone in that, and I expect it to do what most other niche rounds do, enjoy a fair amount of popularity at first, then as time goes on, interest (and new sales) fades. Often to the point where the makers drop production of the guns, and eventually the ammo as well.
Or keep making small amounts of ammo on a "seasonal" basis. SO, stock up, now, while you can. Remember, even the finest rifles aren't worth as much if there's no ammo.