300 Aac Blackout (300blk)

[Mike Bell]

Stupid question...can somebody refreash my memory on "CIP" I cant remember what it is....

[rsilvers]

http://en.wikipedia.org/wiki/Commiss...Feu_Portatives

[Mike Bell]

Thanks, I should have just looked it up because I was thinking of C.U.P.

[rsilvers]

http://www.silencertalk.com/forum/vi...?f=128&t=64797

[carcass]

I realize this is a somewhat older thread but I thought I'd ask here.

Originally Posted by rsilvers

Suggested subsonic load:

• R-P 300 AAC BLACKOUT brass
• Remington 7.5 primers
• 11.2 grains of AA 1680 powder
• Case length is 1.368 +0.000 -0.020
• Sierra 220 MK loaded to 2.089 OAL (this length is optimal for reliable feeding from USGI magazines)
• Chamber pressure 21,100 psi.

What barrel length will result in this being subsonic? I have a 7.5" barrel that I chambered for "300 Fireball" or whatever PTG calls their reamer, and I have good reliability with subsonic operation and F/A cycling in an M4 (carbine stock tube with standard recoil buffer) with 9.2 grains of Lilgun, 1.085 OAL, with a chamber pressure of about 33kpsig.

I don't have any 1680 lying around but would like to try this load, but only if it'll work in my short barrel on F/A. BTW, Quickload calculates my load to result in about 8700 psig bore pressure at the gas port position, which is just enough to allow reliable operation. QL calculates your listed load at 8500 psig, but with lower efficiency of powder burn (80% vs 97%). The additional mass of powder (gas) at that lower pressure may provide enough momentum to operate the action. The weird thing is that you state chamber pressure of your load at 21.1kpsig, but QL calculates it at 39kpsig. Any idea what the discrepancy is? Is QL not good at calculating at these relatively small case volumes?

Thanks for any info, and I hope I haven't missed an answer to this that someone already posted.

[rsilvers]

A1680 will cycle far more easily than Lil-Gun at the same bullet velocity.

QuickLoad with the 300-221 chamber?

300 AAC BLACKOUT has lower pressure than 300-221. The longer throat makes it act as if it had a larger powder capacity.

You need a chronograph and have to set the powder to be in the 950-1020 range with your upper.


Suggested subsonic load:

• R-P 300 AAC BLACKOUT brass
• Remington 7.5 primers
• 11.2 - 11.6 grains of A1680 powder (Adjust powder charge as needed. Factory ammo is 1010 fps for 16" barrel)
• Case length is 1.368 +0.000 -0.020
• Sierra 220 MK loaded to 2.089 OAL (this length is optimal for reliable feeding from USGI magazines)
• Chamber pressure 21,100 psi.

[carcass]

Thanks for the reply!

Originally Posted by rsilvers

A1680 will cycle far more easily than Lil-Gun at the same bullet velocity.

is that because of the increased mass of gas?

QuickLoad with the 300-221 chamber?

yes, i don't think they have the blackout chamber in my version of the software

300 AAC BLACKOUT has lower pressure than 300-221. The longer throat makes it act as if it had a larger powder capacity.

I see.

You need a chronograph and have to set the powder to be in the 950-1020 range with your upper.

Yeah, to build this load I started off making sure feeding was reliable by playing with the OAL & dummies. Then I worked on getting the velocity where I wanted it and then tweaked for reliability on F/A.

Suggested subsonic load:

• R-P 300 AAC BLACKOUT brass
• Remington 7.5 primers
• 11.2 - 11.6 grains of A1680 powder (Adjust powder charge as needed. Factory ammo is 1010 fps for 16" barrel)
• Case length is 1.368 +0.000 -0.020
• Sierra 220 MK loaded to 2.089 OAL (this length is optimal for reliable feeding from USGI magazines)
• Chamber pressure 21,100 psi.

Thanks for the info, I'll have to buy a lbm of 1680.

Two other questions:

1. If I were to buy a bunch of Blackout brass, and resize it to the 300-221 spec with my dies, would it be reliable in a PTG 300-221 chamber?

2. If I were to "touch up" my 300-221 chambers with a new Blackout reamer, would that work, or would there be "missing metal" somewhere that the blackout spec requires?

[Retooferab]

11.2 gns was to fast in my 10.5" ar. Mine needed about 10.4 - .6 gns to stay sub-sonic. It is the 300-221 WTFever.

[rsilvers]

Originally Posted by Retooferab

11.2 gns was to fast in my 10.5" ar. Mine needed about 10.4 - .6 gns to stay sub-sonic. It is the 300-221 WTFever.

Probably because the 330-221 chamber makes higher pressure.

[rsilvers]

Originally Posted by carcass

Two other questions:

1. If I were to buy a bunch of Blackout brass, and resize it to the 300-221 spec with my dies, would it be reliable in a PTG 300-221 chamber?

2. If I were to "touch up" my 300-221 chambers with a new Blackout reamer, would that work, or would there be "missing metal" somewhere that the blackout spec requires?

1. I don't see any reason to resize them.

2. It should work.