I suppose it depends how far out you're shooting to.
Also do you have a preference to short action or long?
Most 7mm's will shoot 162grn bullet.
Totally personal but I would shoot straight 284, 280ai or SAUM
For a truly "long range" (to meet MY criteria of 1000+) projectile, I would be looking at a 175-197gr bullet. Like a Hybrid, Elite Hunter, ELD-X, ELD-M, SMK, VLD (Berger or Matrix), etc.
And for a truly "long range" case design, I would look at a medium to big magnum. 7SAUM, 7WSM, 7SS, 7.21 Firebird, 7.21 Tomahawk, 7RM, 7LRM, 7STW, 7-300WM, 7RUM, 28 Nosler, 7 Dakota, .284 Jarret, 7 Allen Mag, etc.
If 600-800 is your definition of "long range", that opens up a few more cartridges. .280AI is one of my favorites. .280Rem, .284 Norma (or Win), 7 Sherman, etc.
I would not personally take a shot at big game over 1000 yards. Except coyotes. I will shoot those suckers at any range I see them.
As stated, a lot depends on the distance. Also how you feel about factory brass. There are a good number of 7mm cartridges, but like all others, powder capacity decides the winners. For factory brass, the 7 ultramag and the 7 STW are excellent choices. The 300 Wby case is very easily necked down to 7mm with one pass thru a 7x300 Wby factory die.
No doubt the 7x300 Win mag would be also.
All would be good choices, with the ultra mag having an edge (statisticly) for velocity.
The 7 STW and the 7x300 Wby are clones as for velocity, and a 9 twist works very well with bullets in the 160s, as 168 gr Berger, SMK, and JLK all work well also.
I have been using a 7x300 Wby for about 45 years using 162 gr Hornady bullets from a 9 twist barrel.
Using 7828 powder in barrels of 28" or more velocities of 3400 fps are obtainable. We have also found the 162 to actually shoot flatter out to 1200 yds than the 180 gr. Clearly a case where velocity trumps stated BC.
Like others said, range is a factor in what ur wanting, also what kind of barrel length are you wanting to run?. In my opinion there’s no point shoving a whole bunch of powder down a short(24”) tube. I’m having a 28” 7rm being built and throated for 180eldm or 183smk. Magnums aren’t very efficient, but a longer tube helps that.
Practically speaking, 7mm Rem Mag. Brass is readily available. You can find affordable factory ammo for it at any Wal-Mart, and there's tons of load data out there for reloading.
The 7mm Rem Mag may not be "sexy" compared to modern day 7mm rounds (e.g. 28 Nosler, 7mm STW, etc.), but it hands down works.
I'd say it's the "baseline" for all 7mm magnum cartridges in the long range world. Just some food for thought.
So if I'm wanting to get out to 8-900 ( sorry for not clarifying ) yards are we all thinking 7 rem mag?
I already have a 270 wsm with a redding full length bushing die and 7 pounds of reliiader 26, does that bring the 7wsm into it ?
Will be used for fallow, red and sambar deer ( sambar are similar to elk )
7RM should work great on Sambar and red stag. But I would think about a heavier bullet. The 175 Berger Elite Hunter should serve you well. I run the 180 Hybrid @ 2996fps in mine w. 1:8.5" over H1000, but I run the 175 Elite in my 1:9" .280AI @ 2975fps over RL23.
I would say go with the 7mm Rem Mag. If you want to shoot the 162 ELD it will perform great. You can also jump to a 180 if you want to. As an all-around cartridge with good availability I think it's tough to beat.