what kind of deer and javelinas do you have down there that require a .300 mag?
It's not how big but how far. A close shot is 300 yds. Most of the guys build a box that you can only look one way to hunt out of. It's pretty much a benchrest table with an adjustable rifle rest. They'll usually put out wind flags at the various yardages. Depending on the hunter, the flags start at 300 yds and out to 800 yds. They hunt the pipelines mostly. Most load the 125gr TNT bullets in their 300 mags and at the long yardages, the bullet performs like a game bullet. A game bullet will not reliably expand at the long range.
Feral hogs here run from about 350 lbs to over 500lbs. Javelinas- who cares as long as they're dead. They serve no purpose except to destroy valuable grazing land and a few crops. But they are good at spreading disease. Texas is a Swine quarantine state which means you cannot transport a swine from county to county without documentation from a vet in each county.