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I want a gun I will be able to shoot deer at ranges past 400 easily. Thats just a goal but I would like to get the gun ready. But what do I need to change? Just the barrel and action?
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You already have one. 400 yards is a chip shot for any reasonably accurate 270. The 270 will easily take deer twice that far. Wether the rifle and you can is another story. I don't think you need another caliber. Just more education.
Lots of folks, myself included, regularly shoot the 270 out to 1000. You need a good scope, with repeatable tracking. You need field varified drop/windage charts, and/or a ballistic program. There are some web based ones in the bullets barrels and ballistics section. You need to gain an understanding of exterior ballistics. You need a rangefinder. You need your rifle, load, and you to be accurate. You need a field rest. Most folks use bipods and beanbags.
You've got plenty of bullet to take deer at 400 and further. Just need to learn how to do it. If you're happy with four hundred yards, a rangefinder and one of the ballistic plex scopes would be a good way to go. They too require education to use.
If you just want a 308 caliber of some sort, I'd buy another gun. Rebarreling is likely to cost a minnimum of half the price of a new rifle. Then, you'll have two. /ubbthreads/images/graemlins/grin.gif Pesonally, the 270 is one of my favorite calibers. With good bullets, (accubonds, tsx...) there isn't any north American game it won't work for.
Hope this is helpful. Feel free to ask about anything you don't understand.