Well, I went out and popped a shot through it tonight. The H4350 load must be close to full throttle, as it gave 2968 fps with the 107 Sierra VLD - out of a 25" Krieger 1:8. The cartridge is based on the .22-250 - necked up to 6MM - the shoulder is set back about .130 - then blown out to what looks like about 30 degrees. I don't know too much about it personally - it has a reputation for really good long range accuracy and is very efficient - .243 ballistics with 8 grains less powder. I believe this is a David Tubbs creation.