Bill*B
03-24-2020, 08:42 PM
Creating a reduced load for the .223 Remington, with SR 4756 powder, armchair method.
In the first edition of his Reloading Handbook, Richard Lee posted a table gleaned from
Vihtavuori:
Inner Ballistics Coefficients:
Variable Change Change in Velocity Change in Pressure
bullet weight +10% -4% +8%
charge weight +10% +8% +20%
case volume +10% -3% -13%
temperature +50 degrees F +2% +4%
This didn't make it into the 2nd edition. I expect that it points to the right direction, but is a bit "rough and ready".
The 2nd edition of his Handbook does show pressure tested data for SR 4756 in the .221 Remington Fireball. 7.0 grains under a 70 grain jacketed bullet generates 51,100 cup.
The Fireball has 1.45 cubic centimeters of useful capacity; and the .223 Remington, 1.87 cc. Thus, the .223 has almost 30% more case capacity.
If the VV guidelines hold, 7.0 grains of 4756 in the .223 should generate around 37,250 cup in the larger .223 Remington case, with the same 70 grain bullet.
Since I would prefer to use an 11% lighter 62 grain bullet, pressure can be reduced by another 8% (yes, I threw away a full one % of bullet weight reduction for safety, and ease of calculation). The expected pressure becomes 34,270 cup.
Let's reduce the powder charge by a half grain, or around 7%. 6.5 grains of SR 4756 should produce 29, 475 cup. Even on a hot summer day, it should run under 30, 650.
Our reduced load for the .223 Remington is: 6.5 grains of SR 4756 under a 62 grain Hornady FMJ bullet.
My range is closed due to the current virus fears, so Lord knows when I can actually test it.
In the first edition of his Reloading Handbook, Richard Lee posted a table gleaned from
Vihtavuori:
Inner Ballistics Coefficients:
Variable Change Change in Velocity Change in Pressure
bullet weight +10% -4% +8%
charge weight +10% +8% +20%
case volume +10% -3% -13%
temperature +50 degrees F +2% +4%
This didn't make it into the 2nd edition. I expect that it points to the right direction, but is a bit "rough and ready".
The 2nd edition of his Handbook does show pressure tested data for SR 4756 in the .221 Remington Fireball. 7.0 grains under a 70 grain jacketed bullet generates 51,100 cup.
The Fireball has 1.45 cubic centimeters of useful capacity; and the .223 Remington, 1.87 cc. Thus, the .223 has almost 30% more case capacity.
If the VV guidelines hold, 7.0 grains of 4756 in the .223 should generate around 37,250 cup in the larger .223 Remington case, with the same 70 grain bullet.
Since I would prefer to use an 11% lighter 62 grain bullet, pressure can be reduced by another 8% (yes, I threw away a full one % of bullet weight reduction for safety, and ease of calculation). The expected pressure becomes 34,270 cup.
Let's reduce the powder charge by a half grain, or around 7%. 6.5 grains of SR 4756 should produce 29, 475 cup. Even on a hot summer day, it should run under 30, 650.
Our reduced load for the .223 Remington is: 6.5 grains of SR 4756 under a 62 grain Hornady FMJ bullet.
My range is closed due to the current virus fears, so Lord knows when I can actually test it.