300 SAUM vs 300 WSM questions

[Dildobaggins]

So for the past year or so, I've been pretty obsessed with building a short action 30 cal rifle. A friend is willing to give me a Tikka action that was a 7mm rem mag. I finished my first custom off of a defiance action after going back and fourth between a custom and a Tikka for awhile, and now I can get the Tikka for a $20 FFL transfer fee for some plumbing work I did for him. The gun will be used for some long range plinking and hunting.

So I have a few questions, I can't really find answers to. Forgive me if these are stupid. I'm still quite new to bolt actions.

1.) Why is the 300 wsm vastly more popular than the 300 SAUM? Or so it would seem anyway.

2.) I'd probably get a fixed shoulder barrel from preferred barrels. I wanted to do a krg bravo chassis. Will mag length effect the 300 wsm in a short action, if I'm trying to find a good length off the lands? I don't plan on using bullets any larger than 200 grain. Probably stick around the 150 to 180 grain range.

3.) If it would effect that aspect what is a different chassis option that a Tikka would fit that I can use LA mags on?

4.) Is there more accuracy potential in a 300 wsm vs a 300 SAUM? Can't find any videos on YouTube other than people showing the recoil. Just kinda want the 300 SAUM so I can have some insurance for the mag length. That was my only concern.

Thanks!