The 22 with same weight projectile will shoot flatter with a better mpbr.
This is exactly backwards. Given the same case volume and equal peak pressure/pressure curve, the 6mm will drive the same weight bullet faster, increasing maximum point blank range (MPBR) relative to a .22. The increased muzzle velocity for the 6mm is simple physics -- the same pressure pushing on a larger bullet base area (18% more area in the case of 0.243
vs. 0.224) produces more force, hence more acceleration on the same mass of bullet.
The key point is that inside 500 yards, where 99+% of predators are shot, muzzle velocity rules in terms of bullet drop (MPBR), and BC matters very little. Some experimentation with a ballistics calculator will confirm this.
Usually the 6mm bullet will have a lower BC relative to the same weight bullet in a .22, and so will deflect more in the wind at all ranges and -- eventually -- drop more at ranges greater than 500 yards or so. There are important exceptions, though, for coyote hunters. For instance, the BC1 of the 55gr Nosler Ballistic Tip is: 6mm=0.276, .22=0.267. Using 55gr NBTs the 6mm Creedmoor will outperform the 22 Creedmoor in terms of both MPBR and wind deflection at any distance.
If you routinely hunt coyotes in strong winds there is an argument for using high-BC bullets, but you will always be giving up MPBR to get the reduced wind deflection that heavy-for-caliber bullets provide, unless you go to a much bigger case capacity to recover the lost muzzle velocity. Bigger cases mean more recoil and shorter barrel life, although neither of those may matter much to the average coyote hunter.
Attached is a spreadsheet showing some popular lightweight coyote hunting bullets in various calibers, along with their MPBR (maximum rise above line-of-sight = 1.5") at various muzzle velocities, along with typical cartridges capable of producing those velocities. There are some other data of potential interest, as well (e.g., zero range, recoil energy, barrel life).
Based on my analysis of the attached spreadsheet,
I use a 22BR with 40gr NBTs for called coyotes. 95% of the coyotes I have killed were within 250 yards, and way more than half were within 100 yards. I don't have time to use a rangefinder on called coyotes, and I don't call if the wind is anything more than a light breeze, so MPBR is much more important to me than wind deflection. I want to be able to point and shoot without having to estimate range. Light bullets (40gr) and light powder charges (32.9gr) produce minimal recoil even in a walking varminter, which also allows me to see my hits even on coyotes that are close, and to get back on target quickly for those doubles.
