You asked about the fast 7mm/.284's out there first, so I assume that they peak your intrest most. I would encourage you to look at barrel life... I know that alot of hunters say that 700-900 rounds is lots for a hunting rifle. I would say that Long Range hunters would disagree, at least most. when guys want to strech the legs of there rifles, they need to know there rifles. that comes from a lot of trigger time. Severly overbore cartriges are not good for practice. That being said I still want a big 7mm, but I have my go-to guns that dont cook barrels, so it would be more of a toy.
see gone are the days of estimating range using a reticule of some sort, which was marginaly accurate if you were good at it. Then speed really made sense. Now we can accuaratly gauge distance, and focus on the real killer, the wind. 7mm bullets are great at bucking the wind, especially with the new berger 195 coming out, but they still fall short of the .338's.
The .30 cals are a great in between, but personally I see the 7mm's beating them or at least equalling them on most fronts with the exception of the 300 RUM, and 300-.378wby... but then why not get a .338. (dont be mad .30cal guys, keep you inferiority issues to yourself
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As you can tell I love my .338's, starting with the .340 WBY on the bottom end. Why? plain and simple. They do two thing better than anything smaller. the first I have already stated, buck the wind. the second is ENERGY! With the 7mm offerings you can put a hole in the vitals, and if an arrow can kill with a small hole so can a bullet but.... a bigger hole work much better at long range given it is placed just as well.
The down side to the .338's is recoil. Some guys like recoil, some dont. Some like breaks, some dont. Some can handle weight, some wont. So it is up to you to decide what you want. If you want something light then matbe a 7mm is your best bet, but shorten your effective range. If you dont mind a break, or extra weight, or more recoil, or all three... get the .338
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I have used a .338 RUM for 5 years now, and I love it. Rem XCR with a radial brake, bedded. But thats me. .