700 ultra mag chamber build

[GetReel]

I have a 700 SS SPS currently chambered in 300 RUM. I want to build a different configuration. One thing I'm sure of... It will be shot suppressed so 24" max length barrel, preferably 22".
What would be a good, flat shooting cartridge with a "shorter barrel" and ultra mag action?
I'm not as concerned about shooting the highest BC bullet as I am with wanting a flat shooting rifle. Hunting rifle, mule deer, pronghorn whitetail.
26 Nosler? 28 Nosler? Stick with a 300 RUM? 7mm RUM?

 

[shortgrass]

Definitely not a RUM with a 22"-24" barrel!

 

[GLTaylor]

Everything was good til you said short barrel. 100grs of powder takes a minute to burn.
Your best bet is to look at the Sherman Max cartridges. Powder charges drop back to the 70 ish grain level and you can go from 6.5 to .338 diameter. Rich also stocks brass for his wildcats. Look at Shermanwildcatcartridges.com and give him a call. He's very helpful and knowledgeable. I have 2 of his and love them.