How long does a .300 RUM barrel have to be in order to achieve .308 Winchester muzzle velocities?

[rci2950]

https://i.ibb.co/NYgy2xZ/1601780535102.jpg

[Gunreference1]

The .300 RUM has a case capacity of about 110.2 grs of water. The .308 Winchester has a case capacity of about 56 grs of water. The .300 RUM is one of the largest .30 caliber cases available. Is there any reason why you're looking to duplicate .308 Winchester velocities with a .300 RUM cartridge. You would probably need to reload your own .300 RUM to possibly such lower velocities. Factory loads of the .300 RUM will typically always be faster than any factory .308 Winchester loads.

.300 Remington Ultra Magnum - https://en.wikipedia.org/wiki/.300_Remington_Ultra_Magnum

.308 Winchester - https://en.wikipedia.org/wiki/.308_Winchester#:~:text=Cartridge%20dimensions-,The%20.,guns%20alike%2C%20under%20extreme%20condi tions.

Just my $0.02.

Steve