jimbob86 said:
taylor- part of the reason shooting a short barrel is less than enjoyable is the large case capacities of cartridges designed for longer barrels (.308) produce so much undesirable muzzle blast
I very much understand the muzzle blast issues with short barrels. I shot a .280 GNR on a 17.5" including brake, barrel with as both a pistol and carbine on an Encore platform. Think of it as a rimmed 7mm RM shooting 140 grain bullets at 3100 fps based off of the .405 Win cartridge. I hated that barrel and sold it promptly. Plus I have shot several 16" or shorter barreled AR and M-4 rifles.
jimbob86 said:
Part of the original spec requirements laid out by Col. Cooper were:
"The general-purpose rifle will do equally well for all but specialized hunting, as well as for fighting; thus it must be powerful enough to kill any living target of reasonable size. If you insist upon a definition of 'reasonable size,' let us introduce an arbitrary mass figure of about 1,000 lb (454 kg)."[1]
I don't want to try to tackle a 1,000 lb critter with a pea-shooter.
The specs also require a 1 meter max length ... making for a short barrel.
Thanks for clearing up the ft lb issue however there was no standard set in what you just quoted.
1 meter in lenght is easily accomplished even with a 20" barrel. 13.5" LOP, 5" action length, 20" barrel equals roughly 38.5" and a meter is roughly 39.375". Take the Kimber 84M Montana rifle it weighs in at 5.125 lbs so it meets the weight requirements of the scout but it is too long at 41.25" in lenght. However you could shorten the stock by .63" and the barrel b 1" and be just over the 1 meter mark by less than .25". I don't think the Col will roll over about that.
Great news is that after you cut it down you're under the 5 lb mark. So now when you add a rear ghost ring sight, forward rail, front sight post, 7.5 oz Leupold 2.5X scout scope, aluminum rings, ching sling, light weight bi-pod, and 5 rounds (4 down + 1 in the chamber) you have a sub 8 lbs rifle. Probably one the Col himself would be proud to own.
Too bad that rifle just cost you over $2K to make with all the extra work you just had to do just to fill the requirements. I agree that the OP is overthinking the concept a little too much as once I refreshed on the Col's stanadards I was able to build it on paper in less than 15 minutes.
jimbob86 said:
Because the short barrel makes for slower muzzle velocities, efficient bullets are a must. That means boat tails. You can start them just as fast, but they retain velocity (and thus energy) better downrange. It also precludes .30 cal, in my book, as 7mm bullets of the same weight are more efficient..... 6.5's in 140gr are close, but require a 1/8 twist ..... IIRC, you get better velocities at lower pressure the slower the twist rate.....
Cooper wanted a .308 (7-08 where .mil calibers were prohibited) .... I think the 7mm is superior .......
I was simply refering to the statement that the .300 Savage was hard to load for, and my prefrence of flat based bulelts because of the short neck. That way I didn't have to seat the BT below the neck to get enough tension to hold the bullet.
However I think ft lb requirements are pretty much usless numbers as it all boils down to accuracy IMO. If you can get a .308 165 grain bullet to 2650 and a 180 grain bullet to go 2500 fps out of a 20" barrel then you still would only be aroud 1000 ft lbs of energy at 450 meters as I looked up Col Cooper criteria for range. You get roughly the same amount of energy out of the 7-08 with a 140 grain bullet traveling 2800 fps at the muzzle. Plus they all exceed 2000 ft lbs at the muzzle.
However you lack frontal diameter which is a plus IMO to the .30 calibers. 1000 ft lbs of energy at that range is deemed too light by most people who hunt elk and you'll rarely see them weight 1000 lbs. Plus a flat based bullet will make that rage very easily, since "scout rifles" aren't long range rifles. The 7mm cartridges don't have a distinct advantage in trajectory at 450 meters either.
BTW my comparisons were made using JBM ballistcis, the .308 165 grain Nosler Partition, .308 180 grain Sierra Pro Huner, and the 7mm 140 grain Nosler Ballistic Tip.