Not a writer, but I've used the 300 a fair amount, and experiment with a lot of loads for it.
First thing to note, for subsonics, is that you can make much quieter loads for a bolt gun than any of the factory ammo, which is designed to run a semi-auto. The AR15 subsonic loads generally use a slower magnum pistol powder like AA1680 to generate enough gas to cycle the action, but this also makes them a lot louder. For a bolt gun, any of the fast pistol/shotgun powders work well; I normally use Bullseye.
One example I loaded last night is the Lee 200gr RN over 4.5gr Bullseye. This one runs 920-950 fps depending on your barrel, and is very quiet.
For supersonic loads, you want something in the range between AA9 and AA1680. H110/296 and Lil'Gun generally give the best velocity. Lil'Gun gives great velocity with less flash and blast, but I still use H110 a lot as well.
The 300 is also a great cast bullet cartridge for both subsonic and full power loads; are you interested in cast for this one?
Last edited by Yondering; 07/23/15.
