Depends on what 20 gauge shell you are shooting.

A light 7/8 ounce load will kick about the same as a .270. A heavy 3" 1-1/4 ounce load will have close to twice as much recoil as the .270.

Assuming you are shooting about a 6.5 -7 pound shotgun and a typical 7.5 - 8 pound rifle.