300 AAC BLACKOUT questions

[wileecoyote]

I was looking at the 300 AAC Blackout and wanted to get some input from people here. I'm not so concerned about the subsonic stuff because I can't run suppressed.

It looks like it has similar ballistics to 7.62x39 correct? I'm assuming that it wouldn't be nearly as flat shooting as 5.56\6.8 at longer ranges.

I can see the utility for people that have to run super-quiet suppressed because they can just swap ammo and go from a heavy slow cartridge to a lighter faster cardtridge without changing weapons; but I wondered if it brought anything to the table as far as ballistics, recoil and follow up, especially for SBRs.

Any 300 Whisper\Fireball\300-221 users input would be appreciated as it's nearly the same thing right?

edit: Sorry I'm not sure which forum this should go in....

[Stickman]

It looks like it has similar ballistics to 7.62x39 correct?

I'm assuming that it wouldn't be nearly as flat shooting as 5.56\6.8 at longer ranges.

Any 300 Whisper\Fireball\300-221 users input would be appreciated as it's nearly the same thing right?

Correct on all.

[wileecoyote]

Thanks Stickman! Love your pics btw.

Any idea on recoil for the supersonic loads? Where does it fall in the 5.56\6.8\7.62 spectrum?

[fnforme]

I'm also interested in hearing about how recoil is perceived compared to 5.56. The small powder charge leads me to believe recoil will be very similar to 5.56, but I'd like some input from someone with first hand knowledge.

[rsilvers]

http://www.handloads.com/calc/recoil.asp

For the 123 load from an 8 lb 16 inch barrel rifle:
Assuming 19 grains of powder

Recoil Impulse in (lbs sec) 1.6
Velocity of recoiling firearm (fps) 6.44
Free recoil energy in (ft/lbs) 5.16

For M855 from an 8 lb 16 inch barrel rifle:
Assuming 25 grains of powder

Recoil Impulse in (lbs sec) 1.25
Velocity of recoiling firearm (fps) 5.04
Free recoil energy in (ft/lbs) 3.15

From 6.8 SPC, 8 lbs rifle:
Assuming 25 grains of powder

Recoil Impulse in (lbs sec) 1.68
Velocity of recoiling firearm (fps) 6.78
Free recoil energy in (ft/lbs) 5.70

So it has more recoil than 5.56mm and less than 6.8 SPC.

[Todd.K]

Any idea on recoil for the supersonic loads? Where does it fall in the 5.56\6.8\7.62 spectrum?

Pretty close to 6.8 recoil is what I would say. Much less than .308 recoil.

[wileecoyote]

Very interesting stuff, thanks RSilvers & Todd.k.

Lucky for us Noveske will be making them both.....decisions decisions!

[320pf]

My brother and I have shot the 300-221 Fireball at Mystery Mountain 3-gun matches using both subsonic and super sonic loads. The subsonic loads have much less recoil (see below).

300-221 Fireball subsonic load (175g MK @1050 with a 8gr charge of AA#)
Recoil Impulse in (lbs sec) 0.96
Velocity of recoiling firearm (fps) 3.85
Free recoil energy in (ft/lbs) 1.84

If you sight your rifle to shoot the 125g (Speer TNT) bullet 5 in. high at 100 yrds, your zero will be at about 220 yrds., and 5 in. low at 260 yrds. At about 290 yrds you will be about 10 in. low. So a "lollipop" hold on a 10 in plate will give you a hit out to about 200-210 yrds. A 12 o-clock hold will give you a hit out to about 290-300.

Interestingly, with the same site setting. a 175 gr subsonic load, the "zero" point of aim (±0.5 in.) is from 10-50yrds, and about 10 in low at 110 yrds. So from about 75 -to-110 yrds a 12 o-clock hold will hit within a 10 in plate.

I hope this is useful

320pf

[fastpat]

Excellent info, 320pf, what were the 7mm Whisper folks doing?

[320pf]

Actually, there are not very many 7mm whispers out there because the 7mm does not offer any advantage in the sub-sonic realm.

There has been some questioning about why the 30 cal was chosen over the 7mm. Well, with sub-sonics the loads are limited to about 1050-1080fps, so the only way to increase bullet energy is to increase bullet weight. The heaviest 7mm bullet with a high BC that is readily available is the 175 g MK. Here are the BC data for this bullet:

.608 @ 2100 fps and above
.582 between 2100 and 1530 fps
.532 between 1530 and 1300 fps
.500 @ 1300 fps and below

In contrast, the heaviest .308 cal bullet with a high BC that is readily available is the 240 g MK. Here are the BC data for this bullet:

.711 @ 2150 fps and above
.702 between 2150 and 1800 fps
.685 @ 1800 fps and below

So as you can see, the 240g MK has much better sub-sonic ballistics than the 7mm bullet. A 300g .338 cal bullet would be even better but a .338 cal bullet does not leave much of a shoulder to work with using a 223 case. One could consider the 338 Specter but you are not using a 223 case so you have to invest in different mags and bolt/carrier group.

The reason we did not use 240g MK in the 3-gun match is that all of the shots are within about 50 yrds and 240g bullets are much more expensive than 175g surplus bullets.

I hope this helps.

320pf