That's one of my first models, i'm a beginner so there's a lot to learn for me. Even now, just after i've finished this model there are some things i would do differently ;) I've created a kind of parent tree in order to make it easier to move and adjust, metal cage is the main parent object and then there are other muzzle parts connected to it and to each other.
That beautifully looking leather material was created by user elbrujodelatribu and it's available at http://www.blendswap.com/blends/view/66659.
Metal material was previously used in this blend http://www.blendswap.com/blends/view/25094 and was made by monteiro.
It would be great to know what could be done better :)
I hope you find this model useful, use it anyway you want and don't forget to give proper credits to the guys that i've mentioned above. They did great job by making these materials, I can only hope that someday i'll learn how to do that too :)
P.S. English isn't my native language, so don't pay attention if i've wrote something stupid :D