AmericanFrost
Member
Please forgive me if this question has been asked already, but how do the various .300 AAC Blackout bullets out there fare against common bullets in 5.56mm, 6.8mm, and 6.5mm at longer ranges like 300 to 600 yards?
You seldom see momentum mentioned in the Gun press, and when it is it is often misunderstood.
One can think of energy absorption (of a target) as Force x Distance, and momentum absorption as Force x Time. Hence, the heavier but slower bullet with the same energy will travel the same distance in the absorbing material, but because of larger momentum, will take a longer time doing it. It will therefore also impart a greater "kick" to the absorber object.
When talking about firearms, Kinetic energy is expressed in terms of "Foot-pounds". 200 ftlbs is theoretically the energy needed to move a one pound weight 200ft vertically off the ground, or a 200lb weight one foot, or a 100lb weight two feet, etc. However, the KE is a scalar quantity, with magnitude but no direction.
To illustrate this, lets consider a 150gr bullet impacting at 2700fps, giving a terminal energy of 2,428 ftlbs. If fired against a 400lb object it should move it 6ft off the ground, or a similar distance if hit from the side. A 200lb object should be thrown nearly 12ft. Obviously we don't see anything like this in the real world. Even if we allow for the friction of the ground and elasticity of tissue, a man or deer hit by such a bullet doesn't move anything like this distance. This is because the movement of an object hit by a projectile is determined by the momentum, not the kinetic energy.
The 150gr bullet has a terminal momentum of 57.8ftlb/sec, which will move our 400lb target back at a speed of no more than 1.7" per sec. This correlates with what we see in the real world. A deer hit by a bullet flinches rather than being thrown several yards.
Now let us compare that bullet to another projectile, a 1lb cannon ball with the same 2,428 ftlbs of terminal energy. This ball would be moving at 395fps, which does not sound much in firearms terms, but is about 269mph. Since the ball weighs a pound, momentum will be 395ftlbs/sec. That should move our 400lb target back at a speed of 11.85" per sec, which sounds credible for a projectile of this weight and speed.
The difference between a 1lb cannon ball and 150gr bullet is obviously extreme. Is what we have seen significant with smaller differences in projectile weights? If we calculate the momentum for two more bullets with the same energy, we get a 200gr at 2338fps giving 66.8ftlbs/sec and a 250gr at 2091fps giving 74.68ftlbs/sec.
Bubba thinks 7.62 NATO (7.62x51) is "that AK round" (7.62x39).
300 Blackout shoots just like a .30-30
...the AAC will stick around for a while, I do not think it will ever be as popular or widespread as the 5.56 or even the 6.8 SPC.
Gtscotty, I won't try to convence you to use .300 AAC Blackout, since your mind is already made up.
I guess I just don't see how the 300 BLK offers me anything over the 6.8 SPC II, 6.5 Grendel, or the aforementioned 6.5 BR.
For most hunters, a lightweight 16" barrel AR with this performance is a great hunting platform!
What makes you think that?
What's easier for a manufacturer to support?
A cartridge that needs only a barrel change or a cartridge that needs a new barrel, new magazine, and new bolt?
When you're shipping 100 to 1,000 rifles per month, if the barrel is the only difference between two product lines, the choice is easy.
.300 Blackout is the easiest cartridge to support next to 5.56mm NATO. That fact will automatically make it the "winner".
Fellow North Georgian here. We've probably met a few of the same Bubbas.Ha ha, you must live somewhere near me, I believe I may have met your buddy Bubba a time or two.
Some of my best friends are Bubbas. They aren't ballistics nerds like me, but they're great shots, and always seem to have their freezers full of venison. Bubba is good people.ugaarguy,
Bubba might be able to teach us one thing or two. LOL!
I'm guilty of oversimplifying things. .30-30 Win is just the closest comparison. I've blown a few folks minds showing them load data & velocities on 7-30 Waters. It may not be high pressure, but that big ole .30-30 case necked down can sling 7mm bullets mighty fast.The blackout and russian round simply do not have the case capacity to be able do that.
I'm not saying that the .300 BLK won't work for hunting, I was merely posing the question of why I (and others of my ilk) should choose the 300 BLK when there are other existing AR rounds that, leave the barrel faster, hold on to their velocity better, and offer better penetration on the target (given equal bullet construction and weight). Again, I'm not saying the 300 BLK is a bad round, but just because it can be used to hunt doesn't mean there aren't better existing rounds for that purpose. Because of this, I still think it will likely be relegated to a niche status, but then again I've been wrong before.
From what I can see, the .300 Blackout is a more versatile round. It can perform as well, practically speaking, as 6.8mm SPC supersonic. It can also perform very well subsonic which the 6.8mm SPC cannot do well. It can also work in a standard AR magazine and bolt which the 6.8mm SPC obviously doesn't do either.
In summary, while the 6.8mm SPC got here first, there isn't anything it does that the .300 Blackout can't do just as well. The .300 Blackout is more versatile and can do things the 6.8mm SPC can't do well.
I guess it is possible I have not found it in a search... is there a thread out there anywhere discussing the specific performance tradoffs between the various barrel lengths; specifically between the 9" and 12.5"? Why did AAC bother to make these two lengths, this close together?
Gtscotty said:I guess I just don't see how the 300 BLK offers me anything over the 6.8 SPC II, 6.5 Grendel, or the aforementioned 6.5 BR.
If you renamed the 6.8 SPC II the .270 AR-15, Bubba would get that. When you tell Bubba this .300 Blackout shoots just like a .30-30 but out of his AR-15, uses the same "clips" as his current .223, and he only has to drop this new top end on, Bubba gets that. I know that isn't / wasn't AAC's intent with the cartridge, but it's a nice alternate market.