I finally got to having my 450 Ultra Magnum built several months ago( .375 RUM necked up to .458) I had it built on a Rem700 action. Went with a fluted, 26" , 14 twist Lilja, #7 contour. Used a Wyatts center feed extended mag box along with a Greybull stock, 4 port Muscle brake and a shilen trigger. Had Benchmark Barrels do the build. Dave Kiff at Pacific Tool and Gauge did my reamer and RCBS did the custom dies. Did a bunch of load development with the 370gr CEB BBW#13 Non Conventional hollow points but ran out and decided to get a bunch of the Speer 350 gr HotCores and they shot half MOA out to 300 yards if I did my part. I will defiantly be shooting the CEB's in the future when I get a bunch more. With the tip they are 6 times the cost of the HotCores. Drug the setup up on the mountain and crushed the first bull I ran into, the shot was across a deep canyon @ 300 yards. It was a steep down hill shot, had a picture perfect hold off the bipod in the prone. The bull was side ways to me and head down feeding when he took the hit with a Speer 350gr HotCore with a muzzle velocity just shy of 2800 fps. The bullet entered high in line with the pocket about 8" down from the spine and stopped just in the hide at the bottom of the rib cage on the off side. It flat CRUSHED!!! him, he dropped in his shadow and didn't even twitch. 9 hours later I had the last quarter to the truck and the headlights pointed towards home. The rifle when it first arrived pictured with a loaded 450 Ultra Mag cartridge. 370gr CEB BBW#13 Non Conventional Hollow Point with the hi BC polymer tip and yes, they feed from the mag box like glass. The Muscle brake with a extra port machined in the top and a set screw installed by Benchmark Barrels. The 450 Ultra Magnum (Left) Compared to a 500 Jeffery on the right. A closer look at the CEB 370gr Non Con. The rifle zeroed and ready for the field. My first test media for the cartridge. I had to rope fat boy off to a tree, to keep him from falling off the mountain. It was allot steeper than it looks, I know! The recovered bullet weighed 248.4 grs If I do my part the rifle is way close to a half MOA package, not bad for a big bore super magnum. This is the norm for a 200 yard group with the 350gr Speer HotCores. The 405gr Remington bullets even shoot tighter but have a way low BC and I don't feel they will hold together good enough at the velocities I'm pushing them at for big game. I had to try the 405's out. I had read they can't handle 458 Win Mag velocities, it's just not true. I'm pushing the 405's on top of 90gr of Benchmark and using several different powder charges during testing and still touching them all at 100 yards. Should make a good Groundhog load come spring . I have a bunch of Barnes 300gr Tipped TSX's on the way, Im going to see how fast I can get them going and definitely try them on Groundhogs .