New Caliber - 300 AAC Blackout

[constructor]

Silvers,
So the big question, what twist rate are you recommending for the sub loads
optimum and min? forgive me if I missed it.

 

[SharpsDressedMan]

FWIW, my twist rate was 1-8" in a Douglas premium barrel, stabilized the 220's (they are more practical than the 240's due to price), and I got some sub-minute groups with Nosler 125BT's at high end, high velocity loadings, too. Seemed to work well with anything.

 

[Tirod]

Given the table posted, it would appear the correct application is that of a PDW round. Considering the SBR and suppressor connection, it becomes clearer.

Since it doesn't have the ballistics to justify it being a hunting cartridge, then appreciate it for what it does. I don't see the backers claiming it's a hunting round, it would be unfair to say it doesn't make the grade.

As a PDW caliber, whole different story. Let's ignore the OP's original direction and focus on what this is.

All said and done, the ballistics of a cartridge are what they are. It's what shooters think it can be used for that stirs up different opinions. That's when the interpretation of those figures becomes an issue. Like 6.5G being as good as .308 at 800m.

This round is much more about what it can do at 80 meters, and that's where the application is becoming obvious.

 

[MTMilitiaman]

Any piston guns in the near future?

 

[Zak Smith]

Tirod,

That was only the subsonic rounds.

When loaded to full power, these .30-556 cartridges have ballistics more similar to 7.62x39, or .30-30.

 

[rsilvers]

AAC barrels are 1:8 twist for 9 and 16 inch barrels, and we are testing 1:12 for supersonic only 20 inch.

I have heard of people using 6.5 or 7 twist, but have not tried it.

I know that 1:9 twist will sometimes cause yaw with Sierra 220s at 100 yards, when shot at subsonic speeds - so I would not go slower than 1:8 if subsonic capability is important.

 

[benzy2]

So what exactly is the application here? I guess I don't see the point that much. If you load it hot in a 20", its similar to the 6.8 stuff out there. If you load heavy bullets with moderate loads (moderate enough to stay subsonic) you limit yourself in distance. For the slow stuff, why not a pistol caliber conversion in .45ACP? Ammo is much more available and carries similar punch. In the full power middle/light weight stuff why not go with either the 6.8 or 6.5 (depending on application)? I know I am looking at this from a negative point of view, but I'm having troubles seeing what the accomplishment of this round is other than a royalty free .300 Whisper (not that I'm against that). My question would be, why this round rather than a subsonic pistol caliber for the subsonic short barrel side and the 6.8 or 6.5 in the longer barreled version?

 

[MTMilitiaman]

For the slow stuff, why not a pistol caliber conversion in .45ACP? Ammo is much more available and carries similar punch.

The .45 ACP can't even come close to the ballistics of the subsonic load. Remember that even if the velocity and mass are similar at the muzzle, the .30 caliber 220 gr Matchking has a much higher BC than any .451 caliber pistol bullet and is going to maintain better performance for much longer ranges as a result.

The .45 ACP doesn't do much better for velocities from a carbine with any of the chrono results I've seen. About 1000 fps from a standard pressure 230 gr load in a 16 inch barrel appears to be about the norm. Available factory data for 230 gr +P starting out at around 950 fps from a service pistol barrel puts it at between 850 and 900 fps @ 100 yards. For comparison, even from the shorter 9 inch barrel, with a muzzle velocity of 1010 fps, my exterior ballistics software says the 220 gr SMK will still have 976 fps at 100 yards. In fact, this load still has more velocity at 500 yards than some standard pressure .45 ACP loads have at the muzzle when fired from a pistol. And remember, that is just using the stated 9 inch barrel velocity. With a BDC reticule or elevation knob, similar loads have been demonstrated both accurate and lethal out to 300+ yards. I wouldn't expect it to be the Hammer of Thor, and this cartridge still obviously isn't designed to specialize in long range application, but I don't doubt that it is capable of performance well beyond anything the .45 is capable of out to some surprising distances.

 

[Zak Smith]

Here's what the difference is between a 240gr SMK and a 300gr Sierra HP/FN .45-70 bullet

_Bullet_           _BC_ _MV_         0      50     100     150     200     250     300     350     400 | YARDS
240SMK            0.71* 1100 >   -0.00    0.00    4.55   10.98   18.01   25.38   33.00   40.83   48.84 | drop (moa)
300 SHPFN         0.230 1100 >   -0.00    0.00    5.04   12.28   20.41   29.17   38.46   48.25   58.52 | drop (moa)

240SMK            0.71* 1100 >   -2.70   -0.00   -4.76  -17.25  -37.73  -66.45 -103.67 -149.64 -204.60 | drop (inches)
300 SHPFN         0.230 1100 >   -2.70   -0.00   -5.28  -19.29  -42.75  -76.37 -120.84 -176.85 -245.12 | drop (inches)

240SMK            0.71* 1100 >    0.13   -0.02   -0.17   -0.33   -0.49   -0.66   -0.83   -1.01   -1.19 | drop per yard (inches)
300 SHPFN         0.230 1100 >    0.13   -0.02   -0.19   -0.37   -0.57   -0.78   -1.00   -1.24   -1.49 | drop per yard (inches)

240SMK            0.71* 1100 >    1100    1080    1061    1043    1027    1012     997     984     971 | velocity (fps)
300 SHPFN         0.230 1100 >    1100    1044     998     959     926     896     868     843     819 | velocity (fps)

240SMK            0.71* 1100 >    0.00    0.14    0.28    0.42    0.57    0.71    0.86    1.01    1.17 | time (sec)
300 SHPFN         0.230 1100 >    0.00    0.14    0.29    0.44    0.60    0.76    0.93    1.11    1.29 | time (sec)

 

[MinnMooney]

I'm certainly not "blown away" with what I've seen so far. I see hype and average ballistics.... nothing more. The 6.8 SPC has more umph and better downrange ballistics.
I think that anymore research is wasted and "the last word" in cartridges for the AR-15 platform has already been written.

 

[68wj]

I'm certainly not "blown away" with what I've seen so far. I see hype and average ballistics.... nothing more. The 6.8 SPC has more umph and better downrange ballistics.
I think that anymore research is wasted and "the last word" in cartridges for the AR-15 platform has already been written.

Pretty bold statement. While I also subscribe to the 6.8, I don't think we need to call it quits on the R&D side either. There will always be room for improvement. If a general purpose cartridge doesn't meet your needs and is too much of a compromise, why not utilize something that will (ie 300 blk and suppressed SBR).

Besides, the 6.8's initial performance was fairly unimpressive too (due to a number of miscalculations) and has only recently found its legs due to some incredible work by a relative few enthusiasts. People are just now starting to take notice and see the potential there.

 

[highorder]

Troll?

3 year member, with 1500+ posts?...

Thanks for contributing to the conversation.

 

[S. Hill]

Hey Zak, since you have that fancy new computer and software.....

... can you calculate the point blank range for a 5" +- with the 240 gr. SMK bullet? Can you also calculate the relative energies @ 300 yds?

Looking at your chart, I guess you would be talking about pushing the .45 cal., 300 gr. bullet @ 1100 fps. out of something like the .450 Bushmaster? Obviously you wouldn't be able to do that out of a .45 ACP.

I'm surprised that the .45 cal. "pumpkin" holds it's velocity at the longer ranges. It doesn't fall off as fast as I would have thought.

 

[Zak Smith]

This is close

_Bullet_           _BC_ _MV_         0      50     100     150     200     250     300     350     400 | YARDS
240SMK            0.71* 1100 >   -2.70    4.01    3.26   -5.22  -21.69  -46.41  -79.62 -121.58 -172.53 | drop (inches)
                                  elevation maxima 4.62" at 70.12
300 SHPFN         0.230 1100 >   -2.70    4.46    3.64   -5.91  -24.92  -54.07  -94.08 -145.63 -209.45 | drop (inches)
                                  elevation maxima 5.13" at 70.26

240SMK            0.71* 1100 >    1100    1080    1061    1043    1027    1012     997     984     971 | velocity (fps)
300 SHPFN         0.230 1100 >    1100    1044     998     959     925     896     868     843     819 | velocity (fps)

Zero is set to 125 yards on both.


FYI, I chose that bullet to give the .45 load the benefit of the doubt per the BC value.

 

[MTMilitiaman]

I'm certainly not "blown away" with what I've seen so far. I see hype and average ballistics.... nothing more.

Funny, I said the same thing about the 6.8 when it came out.

The 6.8 SPC has more umph and better downrange ballistics. I think that anymore research is wasted and "the last word" in cartridges for the AR-15 platform has already been written.

Yep, but if we are considering "umph" and "downrange ballistics," it's not the 6.8, but rather the 6.5 Grendel.

I know what people expect. It's still an intermediate powered assault rifle round. As such, I don't think anyone has any right to expect much of it past 300 yards. Is it (.300 BLK) the end-all be-all assault rifle cartridge? Probably not. But it does have some interesting potential.

I would like to see it in a piston gun, and I would like more info on the optics...

 

[S. Hill]

Thanks Zak.

So, at less than 100 yds. you hold on the bottom of the melon, and at 150 yds. you should be holding at the very top. Dang, that's lots of drop!

If you believed J.D. Jones' sales information, you just hold dead on out to 250 yds. with his .300 Whisper. Hmmmm....

 

[Ratdog68]

LOL Ya know what I've began to notice?

Yep, but if we are considering "umph" and "downrange ballistics," it's not the 6.8, but rather the 6.5 Grendel.

More and more... comparisons are made with the 6.8 being the standard... and it's the grendel that ends up with the "me too" mentioning. Folks who are honest with themselves admit that the two are closer to one another than the grendel lovers will admit. The popularity of the 6.8 just definately shines (being the second most popular caliber in the AR platform). The 6.8 is a venerable hunting caliber. Deer, hogs, black bear... even a brown bear taken in Canada by a fella using a Ruger mini in 6.8 (and, that'd be with a SAAMI spec'd chamber, Ruger's 1:10 twist and Remington factory loads... talk about being handicapped). Of course... Constructor popped a bull elk with a 6.8 at (if my rememberer is working correctly tonight) about 370yds. I know of a feller on the 6.8forums BBS that settled in with a 6.8 and was consistently ringing steel at 800ish yds. (This last spring as I recall).

Grizzly with the 6.8 http://forums.accuratereloading.com/eve/forums/a/tpc/f/7621043/m/4721044231
Black Bear with 6.8 http://www.68forums.com/forums/showthread.php?t=12574&highlight=Black+Bear
Constructor's elk with 6.8 http://www.68forums.com/forums/showthread.php?t=2737&highlight=Bull
6.8 to 800yds http://www.68forums.com/forums/showthread.php?t=13619&highlight=Badlands

 

[Jaws]

From the official website:


DESIGN OBJECTIVES
• Create a reliable compact 30-cal solution for the AR platform
• Utilize existing inventory magazines while retaining their full capacity
• Create the optimal platform for sound and flash suppressed fire
• Create compatible supersonic ammo that matches 7.62x39 ballistics
• Provide the ability to penetrate barriers with high-mass projectiles
• Provide all capabilities in a lightweight, durable, low recoiling package

REASONS 7.62x39 wAS NOT CONSIDERED
Extreme cartridge taper This is actually an advantage for a fighting gun.
• Reduces reliability of feeding in AR Magazines Actually the AR mags are the problem (straight at the top and curved half way down)
• Reduces Magazine capacity true
• Cartridge taper induces considerably higher bolt thrust-
exacerbating the AR Bolt's weaknesses Is the weak bolt that's the problem
• Requires a larger Bolt Face which reduces Bolt Locking Lug strength-
exacerbating the AR Bolt's weaknesses the weak bolt again
Limited projectile selection
• 0.311" diameter not a common option in most modern bullets


So this is an just an expensive 7.62x39mm cartridge built around the shortcomings of the AR15.

As someone posted earlier: sometimes you just need a bigger gun.

 

[SharpsDressedMan]

There is ALWAYS a bigger cartridge. If you look at this cartridge as the "silent, heavy, high-ballistic-coefficient, .30 battle cartridge that performs well at distances under 150 yards", then you'll see it for what it is. It isn't made to REPLACE anything. It is designed for possibly the widest variety of CQB applications, works in existing combat weapons, and does MOST of the things that a soldier asks of his rifle at those ranges. It can and WILL perform at longer ranges (with proper optics), and can also use supersonic loadings that rival comparable assualt rifles. There is NEVER going to be one cartridge, one gun, that does everything. 5.56, 5.45, 7.62x39, .300AAC/Whisper, 7.62x51........choose your platform and cartridge for what suits you.

 

[dirtyjim]

ptg already has the reamers & gauges if you decide to build your own

 

[Armed012002]

A .30 caliber cartridge for an AR-15 carbine has been a want of mine for a long time.

My reason is one of logistics.

I currently buy .224 bullets for my AR-15 and .308 bullets for my long range rifle. Buying only .308 bullets (say 168 grain bullets) simplifies reloading components and increases my flexibility.

With my carbine and long range rifle sharing reloading components, I can load cartridges for what I need now, rather than planning in advance. In other words, if I buy 2,000 .224 bullets for my AR-15, I can't use some of those bullets for my long range rifle. I might not need that many bullets for my carbine and run out of bullets for my long range rifle. This is something that's difficult to plan for.

A .308 Winchester AR-10 is an option, but trying to squeeze that cartridge into a carbine the size of the M4 is not practical. I want to keep the ergonomics and weight of the AR-15 unchanged.

I'm interested.

 

[Armed012002]

I'm not very interested in replacing my Magpul Pmags and USGI magazines with new magazines for a new cartridge.

Being able to use existing AR-15 30 round magazines for this new cartridge is impressive.

I hope the 300 AAC Blackout takes off.

 

[Tirod]

The AR bolt isn't weak, it works just fine with the caliber it was designed for. What's weak is attempting to stuff in a larger diameter case. 7.62x39 and other cartridges aren't meant for the AR, and the straight mag well is the proof. They have to use jacked up magazines with extra engineering to even feed reliably. The original gun designed around them had a a cut away mag well to accept a properly designed curved mag that matched the cartridges taper. Even the AR wasn't meant for 30 round mags, we just get away with it.

It's no wonder the proponents of the Russian - cased calibers offer superbolts for the AR to beef it up - the case diameter is excessive for the bolt face when machined in the standard material. A stronger alloy is required.

What the .300 creators did was live with the bolt face and straight mag well rather than force the wrong cartridge into it. A .30 caliber 5.56 case matches what's already there, rather than makes things worse. If it feeds from the issue magazine, even better.

What should be getting scrutiny is whether you want 7.62x39 or .30-30 ballistics. .30 caliber intermediate cartridges have more bullet drop than smaller faster ones. The real focus of this caliber is it's power and range compared to other alternatives.

None of the calibers mentioned are inherently bad or lack moral fiber. They were specifically designed with a unique bias in their performance. How they fit in the AR action can be assessed with an eye to how much compromise is accepted: the 5.56 still needs a curved mag well, the .300 AAC adds the demand for a new barrel, the 6.8 requires a barrel, bolt, and different mags, the 6.5G needs a barrel, superbolt, and has to use jacked up mags, the 7.62x39 at least has cheap ammo to offer with all the other problems.

The problem here is that too many focus on the ammo and not on the overall result. Russian cased ammo in the AR is not an optimum combination, more like a range shooters pet experiment that came out tolerable for their purposes. It's like the offspring of a dachshund and German Shepherd. Only it's mother will love it.

In that regard, the .300 AAC is far ahead in offering the performance without making things worse. What might be asked is whether something else already available is even better.

In the coming age of multi caliber AR's, it might be moot.

 

[Zak Smith]

Tirod, good post.

I was one of the first civilian shooters of 6.8 SPC, back in 2004. In 2008, I built up a 10" .300 Fireball (Whisper) SBR based on a Noveske barrel. I view both as special purpose AR-15 cartridges. In other words, if I have a specific purpose where the .300 Fireball is very well suited - the exact right tool for the job, I'll use it. For the vast majority of training, competition, and fighting applications, the overall package of good 5.56 ammo is the best choice.

I grew up hunting white-tail deer in Wisconsin; on our land, the average shot distance was about 45 yards due to terrain and growth. In fact the last two deer I shot (with a 7x57 and a 6.8 SPC), were shot at distances of about 6 and about 40 yards, respectively.

The .300 Fireball/Whisper/AAC-B is compelling because of two main reasons:

1. full-power ammunition shooting 125 or 150gr bullets can achieve pretty good velocities from even very short (e.g. 10") barrels, IE, around 2000 fps plus or minus. With a point-blank range of about 175 yards - more or less similar to a .30-30. This is an ideal match to the hunting scenario I wrote about before.

2. really heavy subsonic loads pack a big punch, although they do have a short effective point-blank range (about 120 yards)

My .300 Fireball upper sits in the safe most of the time, but when it's the right tool, it is the right tool. I would be quite pleased if .300 AAC-B ammunition will fire safely from my existing .300 FB barrel.

 

[EdLaver]

I just read this entire thread, cartridge could serve some use in a CQB role. For me though, like someone else stated, sometimes you just need a bigger all around caliber. AR10 and the .308 for everything out to 600+ yards for me. I wonder just how many different caliber uppers there are now for the AR? Like 15? 20? 5.56 and .308 are all that is needed IMO.