Trivia: The movie was shot in 1994 but shelved until 1996. Reportedly, this was partially because early test screenings got fantastic audience feedback, and the studio tinkered with throwing a little extra money at the movie and releasing it in theaters. However, they were unable to find a good spot in their release schedule, so it was eventually just released direct-to-video as they had initially intended.
Trivia: The design of the main arachnid-like "bugs" from "Starship Troopers" is actually a slightly modified version of an earlier unused design for the "Shriekers" from this film. Some of the same effects artists worked on both movies.
Trivia: Early in production, the film was reportedly intended to be a theatrical release as the first film became a huge hit on VHS and on cable. However, when original co-stars Kevin Bacon and Reba McEntire were unable to commit for various reasons, the budget was lowered and it became a direct-to-video feature. While this was initially disappointing, it paid off in the long run, as it launched a continuing franchise with a further five sequels and a popular (but short-lived) TV series.
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