I owned a Harris 9-13", nice bipod, but to small when it comes to shooting ground hogs once the grass gets over 6" high.
I now have a 13-27" Shooters Ridge swivel bipod. The swivel is nice, but I usually lock the swivel down so there is minimal movement.
If you have an Encore rifle with the standard forend you might want to upgrade to the Prohunter forend, the bipod locks down alot nicer and the wider forend is easier to grip.