.300 WSM vs. .300 WinMag
From Lyman's 48th Ed. Reloading Handbook:
"Winchester launched their Short Magnum line of cartridges with the .300 WSM in 2001. The .300WSM is Winchester's first completely new cartridge to come along in quite a few years as well as their first non-belted magnum. The appearance of the WSM is very similar to the PPC series of cartreidges and features a slightly rebated rim. Benchrest shooters discovered long ago the inherent accurach advantages of short. stubby cartridges. Many shooters report outstanding accuracy with this cartridge as well as lower percieved recoil. The absence of the belt found on traditional magnum cartridges offers smooth feeding and more positive headspacing. Its 2.100" case length, 35-degree shoulder, and pressure limit of 65,000 psi are desighed to offer magnum level performance in a short action rifle.
"Ballistics of the .300WSM averaged 30 TO 50 FEET PER SECOND BELOW THE FULL SIZED .300 WINCHESTER MAGNUM WHILE CONSUMING AROUND EIGHT TO TEN PERCENT LESS POWDER in our lab tests...."
(Emphasis added.)
So there you have it, the advantages and disadvantages of the .300WSM. IMHO, Bambi will never know the difference, but on your end, you use less powder and get less felt recoil. And the "outstanding accuracy" ain't a bad thing, either.
BTW, it's none of my business, but: If you are reloading and you DON'T have a handbook of loads, for heaven's sake--and yours, too--get one before proceeding, and follow it.