FIREARMS IN PARKS
As of February 22, 2010, a new federal law allows people who can legally possess firearms under applicable federal, state, and local laws, to legally possess firearms in this park.
The Credit Card Accountability Responsibility and Disclosure Act of 2009, was enacted May 22, 2009 and will become effective February 22, 2010. Section 512 of this law; Protecting Americans from Violent Crimes, supersedes the uniform treatment of firearm possession in the national park system outside Alaska under the regulations found at 36 C.F.R. 2.4.
It is the responsibility of visitors to understand and comply with all applicable state, local, and federal firearms laws before entering this park. Yellowstone encompasses parts of Wyoming, Montana, and Idaho. Each state has different regulations and these are listed below.
Federal law also prohibits firearms in certain facilities in this park (such as visitor centers, government offices, etc.); those places are marked with signs at all public entrances. Hunting and discharge of firearms remain prohibited in Yellowstone National Park.
Firearms should not be considered a wildlife protection strategy. Bear spray and other safety precautions are the proven methods for preventing bear and other wildlife interactions.
I found this for you. This will depend on whether your state laws will trump the Fed laws.