Re: 300 Win mag and 178gr
Give that 300 WM some guts. Don't sell yourself short with anything less than a 200 grainer in that rifle. The 300 WM is stout with a 180, but it is capable of much more.
Try a combination of H1000 with a 210 Berger or a 208 A max. Work up from around 74.5 - 77.0 grains with the bullet touching the lands.
If you really want a hammer, put a 230 grain Berger Hybrid on top of a case full of Retumbo. You'd be hard pressed to surpass this kind of long range capability with any other 300 WM load.
I just did a seating depth test at 220 yards with the 230/Retumbo combination with a factory built Remington 5R. It ended up stacking 4 shots into a .6 group with the cold bore shot slightly off the group to make it 1" overall. This was with the bullet seated .010 into the lands on top of 77.5 grains of Retumbo in a Remington case primed with a Fed 215. Velocity was 2830 fps. The only mods I've done to the rifle are Devcon bedding and I installed a Rifle Basix trigger.