Visible crew/equipment: When Burt shoots at the Shrieker with the high-powered rifle, a frame of two before the Shrieker explodes, a wire is visible at the tip of its beak, holding it up. (01:16:45)
Visible crew/equipment: When Burt Gummer is shooting at the Shrieker, in the top left corner of the window you can see a crewmember quickly bash the window causing it to shatter.
Answer: It's a 50 caliber Grizzly Big Bore rifle. They are real. Just put "Grizzly .50 Big Bore" into your search engine and you will find plenty of sites.
Grumpy Scot