Willy, I would say in the neighborhood of 40+ ish%.
When she still had her .284 win, the .300 kicked noticeably less than that when we shot them side by side
Out of the box recoil for a 300saum is rated at 24 for a 180 grain bullet where a 284 is at 17,
It felt more like her 7-08 which is rated at 13 or so.
Per Remington's recoil table. http://www.chuckhawks.com/recoil_table.htm
She has since sold both the 7-08 and the 284 because she just did not use them anymore. She is good well over 300 yards with the .300 and it works for about everything