Well i have to declare that i had a “brain fart”: My assumption that recoil energy is approximately proportional to bullet energy (Ke) at the muzzle is not correct: The barrel acts like a rocket engine when all that hot gas tries to escape from the thin hole at the end of the barrel, and a jet of supersonic gasses is pushing the rifle backwards against your shoulder. And a WSM burns 70 gn of powder compared to 32 - 42 gn for a typical 6 mm. That makes a big difference.
Almost 2/3’rds of the “recoil energy” in the online calculator is dependent on the powder charge. Link to online recoil calculator:
An online calculator that calculates the recoil energy, impulse, and velocity of a firearm according to the firearm's weight, powder charge, bullet weight, and bullet muzzle velocity.
shooterscalculator.com
Change the powder charge to zero, and you will see the big difference the gas flow makes. This calculator is probably making good assumptions for hunting rifles without muzzle brakes, but all (or almost all) PRS rifles will have brakes on them, or ar least a suppressor. So not convinced the online recoil calcultion methodology is entirely correct either: A good brake can divert slightly over half of the gasses sideways (neutralizing the rocket motor effect) - or even backwards, actively counteracting recoil at the expense of significant muzzle blast.
But yes, redoing the calcs using “ShootersCalculator” shows that you need around 1600 fps to get a 300 WSM shooting heavy (240 gn) very high BC 30 cal bullets to equal the recoil energy of a 108 ELDM .243” bullet at 3000 fps, but then the wind drift at 600 yards is 10% higher compared to the 6 mm projectile. But you will have to dial even the 400 yard shots, which will waste time. So NOT practical at all! There is just too much weight in these high BC 30 cal bullets pushing the recoil number way up. Low weight 30 cal bullets like a 180 gn don’t work out either: They will have double the wind drift (at 2,200 fps, where recoil becomes equal).
Doing the same calcs for a 6.5 does work out better. It seems you can get your 6.5 shooting 144 gn Berger Hybrids to have exactly the same recoil as a 108 ELDM from a 6 Creedmoor at 2,250 fps, and fairly similar wind drift (only 10% worse). Or match the wind drift exactly at slightly more recoil. Or pick some compromise number in the middle.
Recoil energy for a 108 at 3000 fps equals 2.96 foot pounds:
For the 6.5 mm, let’s pick the 144 Berger Hybrid and reduce speed until we equal the 2.96 recoil number from before:
BTW: I reduced the powder charge to 10 to try and simulate an aggressive brake, with the high speed gasses generated from 10 grains out of a total of 40 grains of powder being the net remaining force on the rifle, the rest goes sideways (no net effect), and some goes backwards doing some partial cancellation of force. No idea if this is reasonable or not! [Somebody needs to develop a recoil calculator that simulates different muzzle brakes and suppressors.]
Not sure i even have a real conclusion, but maybe if you have an existing 6.5 Creedmoor comp rifle, you were competitive before until the boys all changed over to 6 mm calibers, and you really don’t want to rebarrel yet, consider downloading to 2400 or 2300 fps and shoot out the barrel, then rebarrel in some suitable 6 mm caliber.
I was interested to find out if perhaps there are viable workarounds, like picking super high BC bullets to reduce wind drift when you have to give up so much speed, and maybe adding more weight to the chassis. [I realize these are expensive bullets, and building a second rifle in the correct caliber might be cheaper.]
