Do you have a ballistic program to use to compare the two at different altitudes?
The rifle will not be zeroed at 300 yards, that is a certainty, and you will not even be off your Florida 100yd zero by more than .04 MOA as well, ya .040". The guy obviously doesn't know ballistics very well so consider the source when he offers other advice concerning it too. [img]images/icons/wink.gif[/img] Use what you know and have proven to yourself before the hunt.
What will be most important at LR is how stable your MV will be in the colder temps up there. A slower MV and a lower air density would in effect cancel some of the others effects out, but by how much you'd not know unless it was checked. What I would do: Check MV over a chrono when you get there if you can. If you can't, shoot the load at 300 yards, 700yds and 1000yds and record the come ups in MOA needed. You should already be certain of the BC the bullet has, the MV, and verified drops before heading off on the trip. Print out drop charts for the altitude (7000) and temps you're likely to shoot in. This is where a Kestrel
and a Palm Pilot would be sweet. When you shoot there, the drop chart that indicates the drop you're getting will likely be one at a colder temperature if the loads MV is slower up there, both an air density increase from the cold and/or slower MV will result in more bullet drop. If you print some drops out at various temps with/and various slightly slower MV's you'll find a good combo in one that matches the actual drops you record when firing them there.
Like Len said, the effect of the "100 yard zero changing because of altidude" (air density) is minimal, even at 1000 yards it only amounts to what, less than 1/2" high on the target. But, trajectory changing from what you are used to will mean about 2.5" high at 500yds, 9" high at 700 and, 32" high at 1000 yards... This is what will really kill you, not to mention an error a MV change could cause. But like I said, the MV error would surely be in the opposite direction as the air density error is, and if you correctly compensated for the air density change and didn't figure on what might be a lower, maybe much lower MV, you would without a doubt be then hitting lower than POA.
Good luck on the hunt! Sorry for all the suggestions you probably didn't even need on this, answering questions you didn't even ask. [img]images/icons/grin.gif[/img] [img]images/icons/smile.gif[/img]