Pack mule and toady

The idea behind this creature was that its gun was mounted on a large heavily armoured beast. The beast could withstand attack and the little fellow would use it as cover.
You would have to score hits when it jumped out to fire.
The ammunition this character uses is spherical little creatures with super sharp teeth that bite through the target.
I have called the little guy Toady and the big one Jennifer.

Trying to figure out a spring mechanism for the gun

 I couldn't figure out the little guy and I never got it right