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So which do you want?

Nemo

https://www.americanpartisan.org/20...-comparison-of-5-56x45mm-vs-300-aac-blackout/

Fenix Ammunition: A Ballistic Comparison of 5.56x45mm vs. .300 AAC Blackout
Posted by Patriotman | Feb 19, 2021 | AP Staff, Tactical | 0 |

This article comes from Fenix Ammunition and is reprinted with permission gained via Twitter DM on 2/17/21. Fenix Ammunition has recently made the news because it forces anyone wishing to do business with them to check a box certifying that they did NOT vote for Joe Biden. It is largely symbolic but I also think it does make the person who did vote for them think harder about their choice. They have a great Twitter and they are outspoken Patriots. Check out their products here and, if you order anything, let them know we sent you!

The .300 AAC Blackout (aka .300 BLK, 300 Blackout, and 7.62 x 35mm) cartridge was developed by Advanced Armament Corporation and submitted for standardization to the Sporting Arms and Ammunition Manufacturer's Institute (SAAMI) and approved in 2011. The .300 BLK was developed in response to requests from the military for a standardized cartridge with more energy on target and "punching" power than the standard 5.56x45mm NATO cartridge at close and medium ranges, while maintaining the standard 30 round magazine of the government issued M4/AR-15 rifles.

Advanced Armament was able to achieve this by shortening a .223 Remington/5.56mm brass case and then "necking" up the brass case to utilize a larger, heavier .308"/7.62mm diameter projectile. Since the .300 Blackout shares the same case head dimensions as the .223 Remington / 5.56mm NATO cartridge, it allows use of the same bolt carrier group and magazines as a standard M4/AR-15, making conversion as simple as swapping the barrel and muzzle device. This has made the round extremely popular with the civilian AR-15 market for target shooting, hunting, and defensive use.

Despite reams of data, there is much debate regarding the ballistic advantages and disadvantages of 5.56x45mm as compared to .300 AAC Blackout. In this article, we will discuss several distinct advantages to .300 Blackout primarily in Close Quarters Combat (CQB) and defensive situations.

Projectile Frontal Area

A major advantage of .300 Blackout is the increased "Frontal Area" provided by the larger diameter .308" caliber projectile. Frontal Area is the total area of the circumference of the cylinder represented by the projectile facing the target.



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I have a 10.5" suppressed AR15 in 300 BLK for home defense. I run 200gr subsonic round through it. Still more energy than a 357 magnum at same distance, and I don't have to wake the neighbors.
 

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I've long said that "if" I were to have an SBR or braced pistol as a dedicated home defense gun on the AR platform, I would NOT want it to be in .223/ 5.56 mm. I'd want it to be either a pistol caliber, or, more likely for the sake of keeping all the same components except the barreled upper, the .300 AAC Blackout.

I'd be fine with this round's poor long-range performance past a quarter-mile.
What I'd want would be a lot of energy and massive bullet expansion (or fragmentation) at 10-100 yards. And I'd want both subsonic and supersonic ammo to be readily available.
 

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There are a number of single-stamp integral uppers. Think 9”-10” barrel and welded suppressor for a total of >16”.
 

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And I'd want both subsonic and supersonic ammo to be readily available.
While there's a general issue of ammo availability currently, my understanding is .300 BLK is harder to source due to not being as popular as 5.56mm. Also, it's more expensive than 5.56mm.
 

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Harder find than 223? Well of course it is! But that's like saying .223 is "harder to find" than 22 LR or 12 gauge ammo. It's a distinction without a real difference.

Expense? Sure, in the pre-Covid days .223 ammo could be pretty cheap. I was ready to buy a case of wolf stuff last year for $225 per thousand.

But .300 BO is cheap enough, especially if you are swapping uppers on one dedicated lower (or have 2 different AR carvings, one in each caliber but otherwise set up identically). If you have a lot of trigger time on the same basic weapon, much of your practicing with 223 ammo carries over to make you a better shooter when your gun is wearing the 300 blackout upper.
 

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While there's a general issue of ammo availability currently, my understanding is .300 BLK is harder to source due to not being as popular as 5.56mm. Also, it's more expensive than 5.56mm.
7.62x39 is nearly identical to .300 blk, but is significantly cheaper. I really don't understand the fascination with .300 blk.

5.56 is a completely dissimilar cartridge. Higher velocity, lighter projectile, better range, but harder to suppress.
 

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2 reasons?
300 BLK feeds in mil spec 5.56 mm magazines.
Everybody “knows” how inaccurate 7.62x39 really is.

For availability? If you reload, you should have the ability to convert cases from 5.56 or .223 to 300 BLK.
 

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point #1 7.62 x 39 isn't well suited for the AR-15 platform, especially if you want to share the same magazines, & bolts.

point #2 Subsonic 7.62 x 39 never got popular.
 

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I have a .300 BLK upper for SBR. I got one of the Eotech 300 BLK specific optics. I generally shoot super sonic ammo out of it, primarily for hunting pigs. A lot of the supersonic ammo is very accurate and you get pretty good muzzle energy even out of a short barrel.

I shoot sub sonics from time to time, but mainly just for fun with my suppressor. Would be a great home defense gun. Nice and quiet, low recoil.
 

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2 reasons?
300 BLK feeds in mil spec 5.56 mm magazines.
Everybody "knows" how inaccurate 7.62x39 really is.

For availability? If you reload, you should have the ability to convert cases from 5.56 or .223 to 300 BLK.
I have a CZ 527 in 7.62x39, and it's pretty accurate. Crap ammo in a crap rifle doesn't make the caliber inaccurate. It makes the crap ammo and crap rifles inaccurate.
 

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I have a CZ 527 in 7.62x39, and it's pretty accurate. Crap ammo in a crap rifle doesn't make the caliber inaccurate. It makes the crap ammo and crap rifles inaccurate.
I'm aware, but that doesn't change popular perception.
 

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Ummm.... both. If I was to have one MSR and it wasn't an SBR, then I'm going 5.56/.223 - which I did. After that, an SBR would be nice and I think that .300 is more flexible in that platform, especially as blind_shake said - when you want to go suppressed subsonic.
 

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The general rule I hold to is if the barrel is short and/or I want to suppress it, .300 is going to be my pick. My .300 blk pistol is surprisingly quiet even out of its 8 inch barrel. It's just expensive to feed.
 

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Here is the one extremely important thing that is almost never looked at when comparing 300 BLK: velocity. Rifle bullets expand differently than pistol bullets. Whereas low velocity pistol bullets (all are low velocity, typically 1200fps or less) rely on hydrostatic pressure filling a large hollow point cavity to expand, rifle bullets collapse onto themselves due to high velocity (3000fps +/-). Energy in foot pounds is a measurement of potential energy available. However, to effectively transfer that available energy from the bullet into the target, the bullet must expand--otherwise, it will punch a small hole through the target (assuming soft tissue) similar to how an FMJ pistol bullet performs versus a JHP. Very importantly:

For a rifle bullet to reliably expand, the velocity needs to be greater than ~1800 fps.

For a visual of this, imagine driving your car into a brick wall at 70mph versus 30mph. 70mph and your car will be a crumpled mess. 30mph and you'll have some front end damage but nothing near the 70mph impact.

Now look at the velocities of 300 BLK, especially out of a short barrel. Depending on the bullet weight, you drop under the 1800fps mark somewhere between 80 and 120 yards. After this point, the bullet is going too slow to reliably expand. This makes 300 BLK a short range cartridge, really inside of 150 yards at best. You can push the range longer out of a longer barrel, but many 300 BLK guns are set up with ~9" barrel. This is not to say that 300 BLK is not an effective cartridge--it certainly is, when used within it limitations.

Bonus: the reason for the low velocity is case capacity. You take an already small case, cut it at the shoulder (reducing capacity) and use a bullet twice the weight (or more) of the 55 grain bullet that the case was developed for. You can't put enough powder in the case to increase the velocity.
 

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Er...
Making a claim about 300 BLK performance with respect to other baselines isn‘t akin to comparing apples and oranges but closer to apples vs hamsters. There are completely different use cases and mechanics in play between a 230gr .45 ACP, a 55gr .223, a 500gr .45-70, and a 200gr 300 BLK.

Modern .45 ACP ammo is meant to expand and not over penetrate.
Something like a hard cast .45-70 is meant to do the complete opposite especially through bone.
Most .223 rounds are meant to tumble and not expand (but sometimes fragment).

The velocity difference isn’t a function of case capacity. .45-70 has the highest capacity of anything in my post here but may only crank out 1300 fps with a 405gr hard cast bullet. Part of that is powder burn speed and part of that is an intentional design decision limit case pressure.

If you want to target practice at 600 yards, a subsonic 300 BLK might not be an optimal choice. If you still want rifle performance out of a known platform but with limited dB output for indoor or block-level use then .223 might not be optimal.
 
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