Last first, of course technique affects how well you shoot. That's also a reason why prone is such a good position when it's practical: your weld should be easier to keep consistent, and it should be all bone with the only variable at the fore-end. Some people, of course, use bipods when varminting to remove that as a variable, but a rest or proper sling technique will do quite nicely. Core-Lokt bullets are good bullets, but not in the premium group. You're likely to get a little better accuracy out of others. That doesn't mean your hunting bullet needs to be one of the bonded types (bonding actually makes it harder for the manufacturer to ensure good concentricity), but you do need to try others. 150 grain isn't by any means a short-range weight. It's about as small as you want for adequate sectional density when deer hunting, and you may actually find 160 grain bullets more suitable for deer and other medium game, though your idea of sticking with one bullet for everything has merit, too. That's a tough call for people with only one rifle. After all, you don't really care if your bullet performs optimally on varmints, and there's something to be said for staying with one pet load to be completely familiar with the one you're using.