Hey folks - BPCR Silhouette shooter here.  I've got a good load for pigs, turkeys, and rams, but I'd like to make up a chicken load. My normal slug is 500 grs and 1.325" long. I seat out to just engage the lands, which means I'm compressing the load (63 grs Swiss 1.5F BP) slightly. The new slug is only 300 grs,   and .785" long, and if I seat it out to the lands there's a lot more space in the case.  All but one of the grease grooves are exposed.   

So should I 1) seat it out the lands and use some kind of filler to take up the space, or 2) seat it much deeper in the case, compressing the load like I normally do, and jump to the lands? Will accuracy suffer if i jumps to the lands with a BP load?

Anyone have experience they can share?

Thanks!

I normally shot a 40/65 in BPCR silhouette but when I shoot my 45/70 I shoot the Lyman 457193 bullet with 65 grains of 1 1/2 Swiss. It is an older mold with larger grease grooves than the new ones today. I bought it on ebay some years ago. It shoots as well at 200 meters as my other bullets.

I doubt you'll get good enough accuracy out of that 300 grain bullet. You never know until you try. As Glenn said you can use wads to take up space in the case but NEVER place a wad down on the powder and leave an airspace between the wad and bullet. Completely fill the available space with wads.

The original 1873 trapdoor carbine load was 55 grains of black powder and the 405 gr round nose bullet. The cartridge was filled with wads to take up the space. It is a 140 year old idea that worked then.

So what is your gyroscopic stability factor for each bullet?

Caliber      0.458      Inches            
Bullet Weight      500      Grains            
Bullet Length      1.325      Inches            
Barrel Twist      20      Inches/turn            
muzzle velocity      1200      fps            
Temperature      50      degrees Fahrenheit (59 is standard)            
Pressure      29.92      inches of mercury (29.92 is standard)            
                       
Sg =      2.24                  
                       
Caliber      0.458      Inches            
Bullet Weight      300      Grains            
Bullet Length      0.785      Inches            
Barrel Twist      20      Inches/turn            
muzzle velocity      1250      fps            
Temperature      50      degrees Fahrenheit (59 is standard)            
Pressure      29.92      inches of mercury (29.92 is standard)            
                       
Sg =      5.47                  
                       
Sg shouldn't be less than 1.4 (not enough spin and bullets will tumble eventually).  If Sg is greater than about 2.0 you are overspinning the bullet; you may gain some accuracy by going to a slower twist barrel.      

Long distance shooters attempt to overspin their bullets slightly to compensate for drag over long distances (1000 Yards).                  
     
However with a 300 grain bullet you are grossly overspinning the bullet and may reduce your accuracy shooting chickens even though you have flattened the trajectory or reduced recoil.