Hi BuckM;
I hope you and your son have a great hunt!
Can't help you with the .270, but I shoot Barnes bullets out of every big game rifle I own. These might be a good starting point:
http://www.midwayusa.com/rewriteaproduct/913148
I would strongly suggest you not drink out of the streams. Leave the food to the people claiming to bring you 10 miles from the nearest vehicle access. Bring your favorite treats, for me it is those sour cherries...
I don't know about your horse experience, but a 10+ mile ride sounds pretty darn painful to me, I'd rather walk. Wear the Wrangler jeans with the seams reversed and get a piece of sorbathane for your arse.
I don't know which unit you are hunting, but it would be a great use of your time to read this:
http://wildlife.state.co.us/hunt/BGH..._Guides/SW.pdf
Good luck!
CE