I didnt have good luck with a Bipod on my R700 SPS .270.. with the extra pressure it would throw rounds sproatically..
Thats when i went to using a support underneath the magazine area, where the action screws are. Then my groups shrank dramatically!!
I wouldnt chance a shot on a deer past 300yds with the bipod on my rifle, from 300yds and in it wouldnt make that big a difference.
Just lettin ya know what my issues were..
Now on my 300wm and a good free floating stock i use a 6-9" but is wobbly so im gonna drill holes in the base and tap the bipod bar on the stock so i can secure it with no movement.