This is always a fun topic, and since I reload, I have a little different opinion than those that might shoot at closer ranges, or shoot factory loads. Inside 500 meters, .270. Outside 500 meters, .308 absolutely no contest.
Not a single person mentioned Ballistic Coefficient in thier ramblings about which caliber is the best. I personnally shoot a .270, but it's not the best round. It's flat, it's fast, and has plenty of energy for deer out to and beyond 500 meters; but still not the best. There is a reason that the .308 is the most popular sniper round, it's BC. Is it the most flat shooting? No.... Is it super fast? No..... But it is super STABLE, which makes it the more accurate of the popular rounds. The only two rounds that best the ballistic coefficient, on average, of a .308 is the .338 and the .50 BMG. Both of which are also used currently as military sniper rounds accross the world.
Most deer hunters don't take a shot over 100 to 150 yards. for a magnum rifle cartrige, that is nothing. My average shot is 200+, as I hunt over large corn/bean fields.
The closest shot from that ground blind i'm in is over 200 meters. I have honest to goodness 450+ shots presented to me on a regular basis. The deer don't stray too far from the woodline. The rifle in that picture is a cheapo Marlin XL7, but the trick is it has an expensive Nikon 50mm scope. The optic is always more important than the brand name of the rifle. Most rifles, even the cheap ones, are accurate with a cold barrel. With factory ammo, (hornady superformance SST in 130 gr) I got nickel groups at 100 yards, cold barrel always. With hand loads, I clover leaf my groups at 100.
Point is, the best rounds ballistically are the .308, .338, and the .50 BMG. The only one logical to use for hunting is the .308.
Next point is, if you're not taking shots over 500 yards, the ballistic coefficient really doesn't matter. Soooooooo, if it's a magnum round, who gives a crap which one??? They all perform very similarly out to 300 yards, with a 200 yard zero. The trick for accuracy is finding the gr bullet and brand that your gun likes. Anyone that says the brand and grain doesn't effect accuracy, has probably never seen true accuracy. And consistent sub MOA groups can only be achieved with hand loads.
My Marlin likes Nosler Ballistic tip in 130 gr. 54.5 gr. of IMR 4350, CCI primers, and the brass doesn't matter. I weigh the bullet and the powder on a digital scale to insure it's perfect. The result is pin point accuracy, granted the shooter does thier part.
My next rifle will be a single shot, breech loader, in .308 more than likely. I like the Ruger #1's. It's expensive, but man what a nice gun in a great caliber. Put a 56mm scope on it, and it's a done deal.
I really do like a .270 however. And if you consider light recoil, over all ballistics(including velocity, trajectory, etc..; not just BC), versatility (shoots anything from a 90 gr varmit to a 160 gr ballistic tip for large game), etc... I think it's hard to beat. The 7mm is right there with it. .300 mag is cool and all, but that thing will take your shoulder off. I injured my shoulder in Kuwait, so recoil is a big selling factor for a firearm I am going to shoot regularly.
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