First off it is the 408 cheyenne and it is a new test rifle to I think replace the 50 BMG and it has showed a lot of promise I have the website if you need it i will give it to you. every thing as of now is hand made they are preaty tight liped about where the brass is comming from and the bullets also but if you have a extra 8 grand you can buy one
there web site has every thing you could ever want to know about it have a great weekend: Coyote Slayer
It is based off off an modified 505gibbs case necked down to .408 cal. The test projo has been 419gr made by Lost River Ballistic tech. Ballistic Co-efficient of .900 at a muzzle velocity of 2900 fps. Accuracy is as good as the shooter. How good is it? You make up your own mind.
here is the web address WWW.cheyennetactical.com the last test showed 2300 yards and a ten inch groupe but the scope ran out of windge If you go to the site they break down the whole thing for you and give loading Data for it well good luck and take here have good one:Coyote Slayer