I'm gonna put a lot of detail here to try to get all the info in one post...

I've had a Savage .300 WSM for a while. 24" barrel. I hunted with it for awhile, then I replaced the stock, added CDI bottom metal, etc thinking I was gonna use it as a bench type rifle.

My longest available shooting area is 300yds. Usual hunting shot on my place is 100yds or less.

I decided this rifle was too heavy, loud, and cumbersome to carry around hunting. It has a sporter contour barrel that is too thin to run a suppressor. I started hunting with a 6.5 Grendel SBR suppressed.

I haven't shot it in years, but for all accounts it is a good shooting, accurate rifle. I've thought about selling it, but I hate the fact that I have two magnum rated cans and no magnum rifle to use with them.

I'm thinking about having the barrel cut to 18" and threaded. I've seen some tables that say to expect 300fps loss from 24" to 18". A Google search yields mostly anecdotal opinions (might as well be a 308, etc) with very little practical reference.

I do handload.

The barrel thickness at 18" is .655.

I would be using a Griffin Alpha can attaching with one of their brakes. Would .655 be thick enough to thread for a brake to which a suppressor would attach.

Bottom line is I have a rifle that I don't like and want to modify it so I do like it.

Is this a bad idea?

Since you handload it depends on bullet/powder selection.

As a random example you can expect the following:

220gr with 58gr H-4350 in 24" 2550FPS 3100ftlbs and in 18" 2350FPS 2700ftlbs.

On the other end of the spectrum:

150gr with 66.8gr H-4350 in 24" 3000FPS 3000ftlbs and in 18" 2800FPS 2600ftlbs.

So my answer is that it's not strange or silly or pointless at all.

ETA: Yes 0.655" OD is plenty of meat to thread for a brake to hold a can.

I realize this is a little bit apples to oranges but I have a 18" .308 that I slapped a suppressor on. I was also concerned with velocity loss on a short barrel. It's mostly a non-issue for me. I run a slightly faster powder to make sure everything is burning up before it leaves the barrel. Whereas many would run Varget in .308, I'm running H-4895 which is the same series powder as Varget but slightly faster burn. Additionally, don't discount the little bit of free-bore boost you will get from the suppressor. It's small (normally no higher than 50 fps) but it at least gets back some of the lost velocity.

And it sure beats having a massively long combination of a 24" barrel plus suppressor.

I don't think you are crazy at all.  I am looking at a new Savage 338 WM with a 20" barrel.

They come threaded from the factory.  A factory barrel might be a cost effective way for you to get what you want.

Believe me, I've looked. Can't find one, or not looking in the right places.