"....lightweight mauser 1909 in .300 win mag...."
"....I realized that I am a flincher...."
I'm thinking someone should have "over-thought" the specifications involved with the building of your rifle just a little bit....weight is your friend, not your enemy (unless you are 10 years and under or 70 years and over)
Is there a slight chance you may have causes and effects reversed?
[i.e. the problem is the rifle (not the cartridge) and not you?]
And the recoil sensitivity epidemic rolls on, and on, and on