The short mags offer better headspace control over belted cases. Their rifles can be a little bit shorter also.
The WSM's got to the market first. This was a big advantage. Also the WSM's have an attractive look to them and the SAUM's look small in comparison. The 300 WSM in particular has attractive lines. The way it's going with Remington I don't think any of their short mags will make it.
Same for them with the 6.5 RM and 350 RM.
The low aspect ratio cartridges have to be a better combustion vessel. "If you don't know how to make something then make it round. If you can't make it round then make it square"
None of the short mags are at the maximum case capacity for their bores but the 270 WSM comes close. So they are just reasonable cartridges that will work well (in theory).
In general new cartridges are fun. It's about time we phased out those belts. Next I would like to see a standard length magnum based on that Jeffery case.
The early marketing hype on the WSSM's was that they would have superior accuracy. The proof will be in the shooting.
I know the .300 H&H is a sentimental favorite. Lot's of riflemen want one. It's really not a very good cartridge. My old M 70 in 300 H&H is a big, heavy and clumsy rifle as compared to the WSM rifles today.
I would much rather have a WSM. I have said it before and I will say it again that we fell back a century when the Newton, Shuler or Jeffrey cartridges failed to catch on.
