.300 AAC Blackout Load Data

[Rumbler]

I have been doing some load development this week and have come up with a couple of notable loads in my opinion.

As always DO NOT consider these loads safe in your gun. Work up to these in the case of Supersonic velocities, and work down to them in subsonic velocities. Remember that a load below "manufacturers listed minimums" can be every bit as dangerous as loading beyond "manufacturers listed maximums".

The gun is a 16" AR platform. Standard buffer, carbine length gas system. The barrel is a CMMG heavy barrel in stainless steel with a 1:7 twist.

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9.4gr Hodgdon H110
Winchester small rifle primers
208gr Hornady A-Max
2.260 COAL

1022
1038
1057
1066
1057
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16.2 Hodgdon H110
Winchester small rifle primers
150gr Sierra Game King
2.140 COAL

1998
2009
2011
1999
2006
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I have other loads, just gotta find the notes. Will add to this as I do. I have some 230gr, 168gr, 130gr data that will knock your socks off. Too.

[BlueBronco]

You have a shiney rifle barrel?

[Rumbler]

Uuuuum, yeah.

But I do carry a couple of different colors of drab paint in my big red range bag. Including flat black!

[BR549]

Being a total newbie to reloading, I know nothing...on the lighter loads, subsonic, how much of the case is "empty" if there is less powder inside? If a case has a void in it, and the round lays on it's side with the powder sloshed up toward the front of the round, is there a risk of power not being ignited? I always wondered that. Most every factory load I ever took apart was full to the brim with powder.

[FLT]

The small capacity of the 300BLK is ideal for subsonic loads that is in fact one of the primary reasons it was developed. The loads that Rumbler list for the 208 grain subsonic load fills the case about half full and doesn't create a problem . The danger as he stated is that if you start at to low of a charge there is a danger of having a bullet get stuck in the barrel that is why you start a little high and work your way down to subsonic .

[Rumbler]

18.2gr Hodgdon H110
Winchester small rifle primers
125gr Hornady SST
2.091 COAL (crimp to canelature)

2195
2198
2207
2200
2203
This is JD's hog busting load. He says "they don't take a step, they just roll over dead".
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[Rumbler]

FLT is right.

But there is more to it than that. Depending on the load, bullet weight, and powder used, the subsonic .300 Blackout generated between 35,000 - 40,000 PSI of pressure.

Ain't no barrel going to stand that outside a ballistics testing lab where the barrel is 8" in diameter with a .308 hole through the center of it.


So . . . time in the bore, and gas expansion rate also comes into play. In the case of ALL the things we think of as modern firearms a great deal of science is put into the speed of gas expansion versus barrel length.

You can see this in action in any gun that shoots a ball of fire out the end when discharged. THAT is like smoking your tires at the drag strip; it looks cool, but it is actually not what you want because it is non, or even counter productive. That ball of fire is powder being burned AFTER the bullet has left the barrel.

Anyway, back on track . . . the problem with "below minimum loads" can be that the pressure spikes too soon. Before the container (the space behind the bullet to the back of the cartridge case) is large enough to accommodate it without catastrophic failure.

Remember that pressure/volume relationships are inversely proportional, and that resistance to flow is what causes pressure. The farther down the barrel the bullet gets the more pressure there can be without 'blowing up' the person or the gun.

It gets pretty scientific, right up until you 'go to far' then it simply gets really painful . . . or not.

[FLT]

Rumbler are you using cases formed from 5.56 brass for these loads?

[Rumbler]

Yes. 100%

All NATO brass.

[marcus6176]

Yes. 100%

All NATO brass.

I did all the brass conversion for them. I knew it would not be long before mike went over to the black side