Military Times article on new 300 AAC BLACKOUT

[OnPointFirearms]

[RAM Engineer]

Seems like the .300 Whisper, but with the backing of a major firearms consortium. Now that Alabama allows SBRs, I'm interested...

[FromMyColdDeadHand]

What kind of twist do you need to stabilize a 220gr bullet from a subsonic 9inch barrel? 1:8, 1:9??

[rsilvers]

Mers with 300 AAC BLACKOUT upper w/762-SDN-6, subsonic vs. supersonic.


Ti-RANT 9mm on Glock 19 w/147gr subsonic compared to 762-SDN-6 on 300 AAC BLACKOUT upper w/220gr subsonic.

[mtdawg169]

I got to shoot one of these on a 416 lower today at the silencer shoot. I think it was one of the most popular rifles of the day, for sure. The 9" 300 BLK w/ SDN-6 suppressor is an awesome combo. Quiet and controllable. Most of the noise seemed to be generated from the chamber & action cycling when running the subsonic OTM round.

On another note, I was able to witness an impromtu test of the 300 BLK with the Surefire 60 rd. mags. It didn't go so well. Seemed the the different cartridge geometry didn't want to play well with the SF mag.

[rsilvers]

Regarding velocity - 300 Whisper(R) compared to 300 AAC BLACKOUT - if you load both to the same 55,000 psi pressure, the 300 AAC BLACKOUT in a 14.5 inch barrel would be expected to match the 300 Whisper(R) in a 16.1 inch barrel. Or another way to look at it - 300 AAC BLACKOUT in a 16.5 inch barrel would be expected to match a 300 Whisper(R) in an 18 inch barrel.

[Clod Stomper]

Regarding velocity - 300 Whisper(R) compared to 300 AAC BLACKOUT - if you load both to the same 55,000 psi pressure, the 300 AAC BLACKOUT in a 14.5 inch barrel would be expected to match the 300 Whisper(R) in a 16.1 inch barrel. Or another way to look at it - 300 AAC BLACKOUT in a 16.5 inch barrel would be expected to match a 300 Whisper(R) in an 18 inch barrel.

Would you mind explaining this to me? I was under the impression that they have basically the same case capacity.

Thanks,

Will

[rsilvers]

300 AAC BLACKOUT has more velocity potential than 300 Whisper(R) for the same reason that 6.8 SPC-II does over 6.8 SPC.

Upon firing, the case flows into the chamber and meets resistance. The bullet starts to move forward and meets resistance in the throat.

This article shows how throat dimensions play a role in pressure:

http://www.border-barrels.com/articl...Consortium.htm

This is also why the gains of 7.62x40mm over 300 Whisper are larger than the gains over 300 AAC BLACKOUT.

[Clod Stomper]

Thanks. I hadn't thought of that.

I understand how the throat and bore make the difference in the 6.8 SPC and SPCII. I wasn't aware that AAC had changed those dimensions in the .300 Blackout versus the .300 Whisper as well.

Will

[pinzgauer]

This article shows how throat dimensions play a role in pressure:

Yes, looser throats can reduce pressures. But nearly always with other tradeoff's..... And can be carried to extremes! Excessive throats (worn out barrels) also reduce pressure as well, but are not a good thing!

Throats are normally a compromise designed to shoot a range of bullets well. You can optimize them for one ogive/weight/length and see improved accuracy, which often sub-optimizes them for others.

Same for reduced pressure, accuracy is often the tradeoff.

Was the whisper that sub-optimized that it was an easy gain and BLK retains decent accuracy? Or was this a move from a hybrid throat to one optimized for specific loads?