.177 7.8 grn Gamo Redfire vs back of Gopher head/skull

Hi all, today I caught another busy digging up the yard again. I grabbed my Gamo Varmint and loaded a Gamo Redfire 7.8 grn pellet and wacked it in the back of it's head from around 15 ft. with a Gamo Varmint .177 rated at (printed on the barrel) 1250 fps.
From that range I don't think I could have missed. Problem is, I took a shovel to dig it up and found nothing. The ground is super hardpacked and rocky so I didn't get very far yet.
My question is, is that combination enough to penetrate the back of a gophers skull?