Other than ammo availability, is there any reason to select one over the other??

Thanks!!

Supposedly the .300 RCM can match .300 Win Mag performance from a 20" barrel with Hornady's powder. As far as I know the WSM can't quite match the .300 Win Mag in a short barrel (unless you load it with Hornady's special powder).

I'd probably pick the .300 WSM myself. Not only is there a lot more ammo available for it, it comes in a lot more factory rifles. Not that there's necessarily anything wrong with a Ruger, I just like to have options.

Reloading RL-17 in 300 WSM it is quite easy to match or exceed 300 Win Mag for 180 gr bullets.

Otherwise, I agree with kjjm4 about 300 WSM rifle choices. I have had a Mod 70 and Kimber Montana in 300 WSM and both shot sub-MOA.

I'd say more or less it's weather you want a standered size rifle or the more compact ruger.
When I decided to get a 375 I looked at the rifles chambered in the H&H against the rugers and decided to get the shorter compact ruger. preformace the 300 wsm and rcm are to close to call it comes down to the rifle that you like and fits you best