I think you have it a little confused,here is how i understand it.

Most of my research comes from this site and 6mm br and custom builders.

I did a lot of research (finding the science behind it).

If im wrong i hope someone will correct me.

Ballistic coefficient and sectional density are everything.

The higher the bc and the sd,the less drag and wind deflection,on the bullet.

Berger makes a 168g vld for both.i'll compare themm

A 7mm rem mag shooting a 168g berger vld (BC of .617 and sd of .320) and a 300 win mag shooting a 168g berger vld (bc of .473 and sd of .271)

The 7mm will out preform 300 win mag.

The higher bc of the 168g 7mm will catch and pass the low bc of the 168g .308.

By 600 yards,the 7mm should be going faster.

The greater drag on the .308 will slow it down geometrically

By a 1000 yards the 7mm will have passed it.

By 1400 yards the .308 win mag will no longer be super sonic and will

lose accuracy.

The 7mm will be super sonic to 1900 yards.

Even at 600 yards the higher sd of the 7mm should give you better penatration than the low sd of the .308.

To get a 300 win mag to preform as good as a 7mm rem mag,you will need a 215g berger vld.

You might have feeding issues with long 215 vld and have to seat deeper in the case,and will lose powder capacity.

Having to use a heavy 215g bullet will increase recoil.

My research say's with proper parts you can get the 7mm recoil

down to a 243 recoil

7mm;s usually out preform thier counter parts.

7 08 and 308 - 280 and 3006 - 7mm and 300 win mag.

Long distance records held by 6mm are dropping like flies to the 7mm's.

The 7mm berger in 180g hybred is even better,crazy high bc.

The 7mm stw can hold it's own against any .308,but you gain a lot of recoil.

I'm building a 7mm rem mag, here are my parts.

Howa 1500 action.

Benchmark 1 in 9 twist 30 inches.

Nightforce picatiny rail.

Ior steel rings.

Nightforce nxs 3.5-15x56 with zero stop.

laminate thumbhole tactical stock.Ajustable butt and cheek.

The only part missing is the Kirby allen painkiller

muzzle brake(3 port slab),his e-mail said i could order now.

Well that;s my two cents.