308 vs 300AAC

They aren't even close in performance. A 308 will shoot 150 gr bullets 800 fps faster than a 300AAC will shoot 125's. That means considerable more energy and effective range. Current 308 loads beat WW-1 era 30-06 loads by 200 fps, the 300 AAC was designed as a very short range weapon to be used in AR15 platform rifles with bullets fired at very slow speeds so it can be suppressed. It is hard to get much sound reduction from a 308.

A 308 won't fit in an AR15 platform, it requires a much larger,heavier AR10 platform. While the profile and look is similar, the AR10 is much larger and heavier, they are not the same.

What does a .308 AR do that a 300 Blackout can't?

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Everything except run quieter suppressed.

If you are shooting supersonic out of both, I don't know if there is going to be a big difference in suppressed sound level? Muzzle blast will be cut down to near zero on both, and you are going to get a supersonic crack out of both.

Think of supersonic 300blk as a 762x39 that shoots reliably out of an AR15, but that uses better bullets and much more available components.

300blk advantages:
-AR15 standard spec components
-lower recoil
-Makes a fantastic SBR round
-Subsonic loads out there that will run a semiauto reliably

300blk disadvantages:
-Range

308 Advantages:
-Range

308 Disadvantages:
-Every company's platform is a little different... lots of proprietary parts
-Heavier weight of the gun and recoil
-Burns a lot of powder
-Needs longer barrel to maximize the velocity potential
-Subsonic in a semiauto isn't really a thing

I liken the 300aac in supersonic form to being everything the .30 carbine wanted to be, and then some. Even unsuppressed running very heavy bullets over pistol powders i.can be fairly quiet, for a high power rifle. I shoot mine unsupressed using 245mbcs and while i use hearing protection it dosent hurt to shoot it without.

The .308 on the other hand is what id want to shoot anything over 100yds and bigger than 150-200lbs.

If your thinking semi ar take into consideration that the .308 will likely be better for mkre situation, but also has to be built on a larger, heavier, more expensive, platform.

What everyone else has said ...plus....I am a fan of the 300 Blackout having it in two AR's, one AR pistol, a Handirifle and a Ruger American carbine. I have shot a monster Texas hog and many smaller ones with it, one shot as there is seldom time for a second if needed.
There is no comparison in the calibers, .308 and 300 Blackout but at 100 yards or less I can take what I want, deer, hog, varmint etc quickly and efficiently as shot placement is the mark of a good hunter. My buddy shoots all of his deer in the neck thus not wasting a bit of the meat and ammo.

The .300 AAC Blackout, SAAMI short name 300 BLK, also known as 7.62×35mm is a rifle cartridge developed in the United States by Advanced Armament Corporation (AAC) for use in the M4 carbine. Its purpose is to achieve ballistics similar to the 7.62×39mm Soviet cartridge in an AR-15 platform while using standard AR-15 magazines at their normal capacity.

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The above quote was taken from the Wiki. It affords a good overview of the 300 Black cartridge and importantly, why it was developed.

The 7.62×51mm NATO (official NATO nomenclature 7.62 NATO) is a rimless bottlenecked rifle cartridge developed in the 1950s as a standard for small arms among NATO countries. It should not be confused with the similarly named Russian 7.62×54mmR cartridge, a slightly longer rimmed cartridge.

It was introduced in U.S. service in the M14 rifle and M60 machine gun in the late 1950s. The M14 was superseded in U.S. service as the infantry adopted the 5.56×45mm NATO M16. However, the M14 and many other firearms that use the 7.62×51 round remain in service, especially in the case of various sniper rifles, medium machine guns such as the M240, and various rifles in use by special operations forces. The cartridge is used both by infantry and on mounted and crew-served weapons mounted to vehicles, aircraft and ships.

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The above quote was also taken from the WIKI and affords a good overview of the 308 Winchester or 7.62 X 51 NATO.

The two cartridges were designed for two very different purposes and really share nothing in common making a comparison difficult since we really do not have apples to apples for comparison purposes. What is important is to note how each cartridge serves a specific purpose and when we choose a firearm we choose the gun and caliber to fit our intended purpose. While the 300 Black has its purpose it really is no match for the .308 Winchester unless of course we want the unique features of the 300 Black.

Ron

They're really for two different purposes. .300AAC is for 0-400m with the ability to run suppressed, .308 is for 0-800m. I would advise against hunting larger game with .300AAC, and I would advise against using .308 for home defense indoors.

There is no wonder cartridge. If there was, that's all we'd be shooting right now...

Grayrock said:

Did a quick search and did not see a thread about this. What does a .308 AR do that a 300 Blackout can't? Energy? Range? Cost? etc...

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Do you really mean 308 Winchester which does not fit in an AR-15?

Or are you thinking of the 30 Remington AR which was designed for the AR-15?

Or something else entirely.

Both are very versatile when it comes to hand loading, with the 308 having more velocity through all bullet weights. No comparison on velocity or range. Reloading components for both are plentiful. 308 brass is cheap, 300 Blk can be obtained fairly cheap but you can also convert 223 brass even cheaper. I built a 300 Blk AR pistol for about $650. $650 will be hard to build something similar in 308. I've shot a 1-inch 5-shot group at 300 yards with a Savage 308, won't find a 300 Blk that will do that.

Apples to oranges. 7.62x39 vs 300 BLK is a much more apt comparison.

Mike

With lightweight AR-10's such as the DPMS GII bucking the trend of massive/heavy rifles, the .308 AR is becoming a much more handy, usable rifle. Heck, at 7lbs, my AR-10 made my 9lb 7.62 Chinese AK instantly obsolete.

Nothing really. However, a .308 will do it father away. Mind you, the BO uses primarily magnum pistol powders like H110 and IMR4227 with that 150 grain bullet. Runs max loads of about 1900 fps. The .308 start loads are between 2500ish and nearly 2800 fps.
The rifles themselves make no difference at all.

I agree with everything said above, but let me ramble on a bit... I have a .308 AR and a .308 bolt action with a 16" threaded barrel, both of which I run suppressed. I also have an internally suppressed 300 BLK AR and a couple of 16" threaded barrel 300 BLK bolt actions, which I run suppressed with same can as used on the .308s. Subsonic .308 and 300 rounds are "Hollywood quiet" in the bolt guns, but not nearly as quiet in the AR's, because of the noise of the action. My .308 AR (a POF) will not cycle subsonic rounds, so you might as well use a bolt gun if you want a quiet report. The 300 AR (a Leonidas) will cycle both subs and supers. My 308's like Remington Hog Hunter. I haven't found a particularly accurate subsonic round for my 300 AR yet, but with an 8" barrel, I'm not expecting a lot.

Walkalong said:

Two totally different calibers, except for bullet diameter, at very different power levels, for totally different applications.

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But on the other side of the coin, they can use the same cheap 147 grain FMJ bullets for very economical blasting ammo.

300 BLK is a great cartridge for what it was designed for and so it the 308.

The two cartridges use the same bullets but .308 uses twice as much gunpowder behind it. Having the same bullets does not make them the same, cartridges are selected because they have different levels of power and range.

You can have a more powerful cartridge using a smaller bullet with higher speed than another with a larger, slower bullet. It's a major source of discussion on the internet when posters ignore the amount of powder behind the bullets. Aerodynamic efficiency can held retain the power a bullet can have but it is based on the powder load, first and foremost.

Grayrock said:

Did a quick search and did not see a thread about this. What does a .308 AR do that a 300 Blackout can't? Energy? Range? Cost? etc...

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About 800 fps.

I built myself an AR in 5.56 and a friend asked me to build him one. He had originally asked for .300 BLK. I have procured a lower parts kit (with stock), a custom charging handle and ejection port cover. I already purchased a couple of mags and a couple boxes of ammo. I was fixing to order a lower receiver when my buddy tells me he is thinking of .308 now. So... I am trying to get an argument formulated to convince him to stick with the original plan. I do need to query him as to his primary use for the weapon. Perhaps that should give a better perspective regarding my original question.

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The guns are completely different size since the .308 is too long to fit in the normal AR15 receiver... AR15 top, AR10 bottom:



The only parts you have bought so far that might work will be the trigger group... everything else will need to be replaced (charging handle, receivers, magazines, ammo obviously, etc)

No, 6.8 and 6.5 mags and bolts are proprietary.

6.8 SPC uses different mags, can be found for about $15-20. It indeed bridges the gap between the rounds both distance and power.

6.8spc mags and bolts aren't proprietary (nor are Grendel's). I believe he meant to say the 6.8spc mags and bolts are not compatible with 5.56/223 cartridges, and vice versa. They're cartridge specific, but not proprietary.

The 6.8SPC and the 6.5 Grendel are far and away better choices for long range hunting and shooting than the 300blackout. The only disadvantage is the opportunity to run sub-sonic, but for hunting purposes, or even range plinking, suppressed super-sonic rounds are effectively as quiet as is ever needed, and the extra power is well worth the extra crack.

Claiming the 300 blackout is capable of 0-400m is disingenuous. This might be true on paper, but for anything you're wanting to kill, it's more like 0-200m. I was shooting and hunting with a 300blackout long before AAC ever staked their claim to it - as the 30 Whisper - and it's never been anything impressive for me. Suppressed, there are better rounds, super-sonic, there are better rounds...

For ANY of these, the 308win is far more powerful with a far greater range. I've shot 6.5Grendels to 1,000yrds with good success, 6.8spc's to 800yrds as well, have ran 308win's past 1,600yrds... I've killed game with 308win's past ranges where the shorter AR-15 compatible cartridges peter out even on paper...

Ive fed a 6.5s from a 20rnd 5.56 mag, BUT only 2 rounds will stack properly..ish....so no it dosent really work, but can be dun in a pinch.

The cost of mags switching to 6.5 or 6.8 isnt a big deal, and you get much better on game performance as has been said already. Barrels, and bolts arnt much more then decent 5.56/300aac counter parts, and ive seen some of each on ebay in the 100-150 dollar range if you wanna be cheap cheap.
One thing to take into account with the 6.5 is that there ARE 2 bolt face styles, recessed and non recessed, this effects the headspace. If you purchase a bolt and barrel together they should be the same. I havent seen any major manufacturer that used the non-recessed bolt face (recessed means that the face is deeper than a standard 5.56, generally considered to be the "correct" way to build a grendel or x39 bolt). Other then that, what little extra cost is involved in going to the larger rounds i feel is more than made up for in performance.

Other options that keep the standard mags, bolts, AND standard cases would be the various x45 or x223 rounds. Only the 6x45 I believe is available in factory ammo, so you these would be best for a person who reloads.

I have a 6x47, which is basically a slightly longer 6x45, and have had great results with it.