It takes me several minutes to shoot it in my girlfriends ass. The first time it took a lot longer becasue she was so nervous it seemed to take longer to go in. You just got stay relaxed and not tighten up. (It hurts a lot less if you take it slow!) Sometimes I even watch the clock and a 3 cc shot could take as long as 3 minutes. If you get a little oil on the outside of the "pin" as you call it, it will glide in a little easier.
The problem is, I have a hard time reaching around to pop mysself in the ass. I'm too tight and my arms / shoulders will cramp up. I tend to do my legs, tris and delts a lot more but that is for 1cc shots of winny. sometimes for 1cc I will take at least 2 minutes.
Hope that helps. (some humor but some truth as well.)