<<Win42 >> You probably have several things going on.
- It sounds like your length of pull is too short for your body (not necessarily how tall you are but your anatomical ratios: neck length, face shape, eye set, cheek bones, shoulder width, upper and lower arm lengths, hand size, body weight).
-The eye relief may not be adjusted properly for your vision in your scope and it may be too far aft in your mounts.
- Your cheek-weld may be tilted too forward causing you too look out of the top of your eyes and putting your forehead in the recoil track of the ocular eyepiece...the crescent cut maker.
-You may be creeping forward on the stock's comb (hint-were you a shotgun shooter?). -Your gun mount may be too low on your pectoral muscle or out of the natural shoulder pocket too far on the point of your shoulder. (hint-do you slightly push the rifle/shotgun forward then pull it back into the proper location or pocket formed with your elbow raised near horizontal or do you just rotate the butt radially into where it catches/stops and go with that??)
-Lets face it a 300 anything is too much gun to shot free recoil in a hunter weight rifle...so how firmly do you pull it into your shoulder and how firmly and where do you grip it.
-Even little things like a palm swell will allow you to take some recoil up with your hand/thumb web.
-It was decades before someone taught me to allow the recoil to ripple thru my body in a semi relaxed state and dissipate throughout the whole body vs being completely rigid and the rifle stopping abruptly at your rigid shoulder/body.
-Since this is LRH and the assumption is that for a good hold you are going prone; is your rifle fitted primarily for that or the normal erect and bench/seated postitions?
By the time you think thru the answers to these questions you should have figured out your own answers...which maybe you are more comfortable with a 7mm or 6.5mm!
Hell, if all else fails take a shooting course from Shawn,Aaron,Darrell*,John but then if we could put our ego aside and do that our IQ would go up. Good luck and watch out for those high angle up shots.