Re: 300 RUM or 7mm with 180 bergers at 3000 fps
I have two 7mm rem mags and two 300 RUM's. Here are the actual average ballistics out of the four where I live at 5000 feet elevation. You are comparing apples and oranges with a mid range cartridge vs a super long range hunting rifle. 180 grain berger vs 180 grain Cutting Edge.
The 7mm drops 84" more with nearly 7" more wind drift at 1000 yards, no contest. The 180 grain bullet out of 300 RUM is traveling about 350 fps faster than the 180 berger at 1000 yards, no contest. The 300 RUM has nearly 550 more foot pounds of energy at 1000 yards, no contest. The 7mm remington is a mid range cartridge and there is no comparison to it against a super long range hunting cartridge. If a long range hunting cartridge is what you are after and a 300 RUM fits your action then this is a no brainer. Why try to make a mid range cartridge into a long range cartridge when you can just get the one that works best to begin with instead of trying to make a very marginal cartridge work long range.
To see how good the 300 RUM is compare it to the 338-378 wby which is the best standard long range cartridge out there. The 338-378 with the 225 grain Cutting Edge bullet only beats the 300 RUM 7.5" in drop, 5" in wind drift and 75 fps in velocity. The 338-378 has a significant advantage of over 500 foot pounds energy because of the heavy 225 grain bullet. These are all actual ballistics out of my rifles with accuracy loads.
So when you are ready for the top of the line long range hunting rifle you can get a custom action and build a 338-378 wby and beat the 7mm by over 90" of drop, over 12" in wind drift, over 400 fps, and over 1100 foot pounds of energy at 1000 yards. Now you are hitting the animal with a large 338 caliber bullet 45 grains heavier that will create exponentially more damage to the animal for quick kills vs wounding loss in the little 7mm. Talk to hunters who have shot animals long range for 30-40 years with all calibers of weapons and have seen hundreds of kills. Then make your decision of a long range hunting rifle.
Predictions are difficult, especially when they involve the future