20” 300win mag 5rR700?

[whitetail regulator]

Looking at cutting a remmy 700 5r 24" 300wm down to 19.5-21" for supressed use only...Not too worried about velocity...more concerned about supressor life...yhm qd phantom 308/ sig srd762 qd
Both are 300win mag rated...but not much info on minimum barrel legenth...chime in with some info please...