I haven't paid too much attention to these rounds and just came accross a box of empty 300's and was impressed with the size of the cartridge. What is the parent cartridge for this ammo?

Your looking at it. E

The .404 Jeffries was the parent cartridge. The Ultras are, of course, much modified from the original.

I had to change my 338 RUM unfortunaly. It was impossible to find any reloading tools in Sweden at the time and paying 4 $ a round was little to much. But it sure was impressive thing to shot. I used the Remington load with 250 grains Swift A-frame, looked like a nuclear bomb cloud when it expended.

With 3 inch over on 100 yards i had it right on at 200 and 4 inch under at 300.

Count me in on the 338 RUM list. I have a Sendero, the only one I have seen, I know they made more I just haven't seen them, anyhow it is amazingly accurate!!! This is a REAL BIG STICK! I have not loaded any 180 Nosler BT's yet but the 200 grain BT's shoot l 1/2" at 200 yds. The first box of factory 250 Swifts, a friend and I bought, Shot under 2" in his SS composite and my Sendero. I have nothing to say but good about the cartridge and gun, yes there is recoil but there is with a 338/378 and a 340 Weatherby. Don't shoot them if you don't like them or load them down and enjoy it like I do.

Good Hunting, "Z"

Sorry, failed to mention that 2" group with the 250 Swifts, was 200 yards, yea it surprised us too. "Z"