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Old 04-20-2020, 06:03 AM   #1
Dexion
 
Join Date: Dec 2012
Default 300 Blackout Caliber

I looking for stats for an AR15 in 300 AAC Blackout or similar.
I searching through HT book but I didn't find anything.
Thanks
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Old 04-20-2020, 07:16 AM   #2
johndallman
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Join Date: Oct 2010
Location: Cambridge, UK
Default Re: 300 Blackout Caliber

300 Blackout was designed to reproduce 7.62x39 ballistics in a cartridge that fits an AR better - the AR isn't designed for tapered cartridges like the AK family is. An additional requirement was that the AR retain its full magazine capacity, which seems to have been achieved.

So you take the M16A1 stats from High-Tech, and change range and damage to those of the AK-47. If your AR conversion is good quality, it has Acc 5, or if it's cheaply produced it has Acc 4. The weight and ammunition weight go up a bit. That's about all.

The resulting rifle isn't much better than an M16, to with the resolution of GURPS.
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Old 04-20-2020, 07:24 AM   #3
Anaraxes
 
Join Date: Sep 2007
Default Re: 300 Blackout Caliber

Wikipedia: "300 AAC Blackout was approved by SAAMI on January 17, 2011."

GURPS High-Tech 4e publication date: November 2007.

Sounds like a job for the Douglas Cole Ballistics Spreadsheet.

If I throw numbers from Wikipedia into it -- and I don't know what I'm doing -- starting wtih the 7.62x39 and just adjusting bullet mass, case length, and chamber pressure, at the max chamber pressure I get a result that's a good bit hotter than the velocity/energy numbers in Wikipedia. (6d damage at 55000 psi). If I cut the pressure down so that the output matches Wiki (675 m/s, 1840 J), I wind up at 40000 psi -- and the damage at that point is 5d+0.
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Old 04-20-2020, 07:27 AM   #4
DouglasCole
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Location: Lakeville, MN
Default Re: 300 Blackout Caliber

Quote:
Originally Posted by Anaraxes View Post
Wikipedia: "300 AAC Blackout was approved by SAAMI on January 17, 2011."

GURPS High-Tech 4e publication date: November 2007.

Sounds like a job for the Douglas Cole Ballistics Spreadsheet.

If I throw numbers from Wikipedia into it -- and I don't know what I'm doing -- starting wtih the 7.62x39 and just adjusting bullet mass, case length, and chamber pressure, at the max chamber pressure I get a result that's a good bit hotter than the velocity/energy numbers in Wikipedia. (6d damage at 55000 psi). If I cut the pressure down so that the output matches Wiki (675 m/s, 1840 J), I wind up at 40000 psi -- and the damage at that point is 5d+0.
I wrote this up as the .300 AAC on the Reloading Press a while ago.
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Old 04-20-2020, 08:39 AM   #5
Anaraxes
 
Join Date: Sep 2007
Default Re: 300 Blackout Caliber

Quote:
Originally Posted by johndallman View Post
300 Blackout was designed to reproduce 7.62x39 ballistics in a cartridge that fits an AR better
That's why I thought starting with those numbers wouldn't be terrible.

Quote:
Originally Posted by DouglasCole View Post
I wrote this up
Great! (Go with those numbers, Dexion :))

Biggest difference from the one I did was powder burn length. (I had 25mm left over from the 7.62x39; 10mm puts the numbers up in the proper range. But not the sort of thing they list in Wikipedia.) Also the chamber bore drops from 10 to 9.2, which is around ~5%.

And it still comes out to 5d from a 14-16" barrel... as johndallman said, there's only so much granularity in the damage dice.

Last edited by Anaraxes; 04-20-2020 at 10:31 AM.
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Old 04-20-2020, 09:59 AM   #6
Dexion
 
Join Date: Dec 2012
Default Re: 300 Blackout Caliber

Yes, thank you very much :)
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