I’m still debating on my next rifle cartridge. I’m considering any 7mm between the 7-08 to 280AI. Will be running a suppressor, barrel length 18”-22”. Build will be based either on my Rem 700 .270, or Tikka.
I recently built an 18" 7-300 wsm improved on a tikka action.
Shooting suppressed I ended up at 2900 with 168 bergers, and 2875 with the 175 ELDX.
If you're set on a non magnum the 280 ai would be your best performer, I'd guess 2750-2800 would be doable at 18" with a 168
The 280AI is always going to outrun a 7-08 no matter what barrel length. There's going to be about 150'ish fps difference between the two but the 280AI is going to use right around 20 more grains of powder to do it.
With a 168 in the 280AI and a 20in tube you'll be around 2850 using 65gr of powder. The 7-08 with same bullet same 20in pipe will be around 2700 using 45gr powder.
What about a 284? A 284 w/168 20in tube will pretty much match the 280AI.
Brass quality favors the 284 and 7-08 as both have easily available Lapua brass.
With that standard bolt face LA Rem 700 you can pretty much make that anything you want because the bolt face is easily opened up so maybe take a look at a 7 SAUM or 7 WSM.
Basically take 25 fps off per inch from known data down to 19 inches and you’ll be close. Your barrel could make it faster or slower it is prolly that close.
I have had several 7mm Dakota xp-100s with 18" barrels. Still have one. Mostly used 180-195s. Current 18" bartlein barrel is shooting 190 matrix at 2785fps with retumbo. RL33 gets more speed but this load shoots good!
Also have a 14" 284win. Use 142 Lehigh controlled chaos @2640 in that.
I have a Remington Model 7 7mm08 with 20 inch barrel. I am using 131 grain Hammer Hunters. With my best load of Varget I am getting 2950fps. I had to put a lot of work into the gun. I replaced the trigger with a Timney and put a new HS stock on it.