Relating to firearms; and declaring an emergency.

Defines "undetectable firearm." Punishes manufacturing, importing, offering for sale or transferring undetectable firearm by maximum of 10 years' imprisonment, $250,000 fine, or both. Punishes possession of undetectable firearm by maximum of 364 days' imprisonment, $6,250 fine, or both, and 10 years' imprisonment, $250,000 fine, or both, upon second and subsequent convictions. Punishes offering for sale, selling or transferring firearm without serial number by maximum of $1,000 fine upon first conviction, 364 days' imprisonment, $6,250 fine, or both, upon second conviction, and 10 years' imprisonment, $250,000 fine, or both, upon third and subsequent convictions. Punishes possession of firearm without serial number occurring on or after September 1, 2024, by maximum of $1,000 fine upon first conviction, 364 days' imprisonment, $6,250 fine, or both, upon second conviction, and 10 years' imprisonment, $250,000 fine, or both, upon third and subsequent convictions. Defines "unfinished frame or receiver." Requires gun dealer to conduct criminal background check before transferring unfinished frame or receiver. Punishes importing, offering for sale or transferring unfinished frame or receiver by maximum of $1,000 fine upon first conviction, 364 days' imprisonment, $6,250 fine, or both, upon second conviction, and 10 years' imprisonment, $250,000 fine, or both, upon third and subsequent convictions. Specifies exceptions. Punishes possession of unserialized unfinished frame or receiver occurring on or after September 1, 2024, by maximum of $1,000 fine upon first conviction, 364 days' imprisonment, $6,250 fine, or both, upon second conviction, and five years' imprisonment, $125,000 fine, or both, upon third and subsequent convictions. Provides that person commits crime if person possesses unfinished frame or receiver and is prohibited from possessing firearms. Punishes by maximum of 364 days' imprisonment, $6,250 fine, or both. Prohibits person under 21 years of age from possessing firearms and unfinished frames and receivers with specified exceptions. Punishes by maximum of 364 days' imprisonment, $6,250 fine, or both. Establishes affirmative defense for person under 21 years of age who owned firearm before effective date of Act or who relinquished firearm prior to prosecution. ] Authorizes governing bodies of certain public entities that own or control public building to adopt policy, ordinance or regulation precluding affirmative defense for possession of firearm in or on public building by concealed handgun licensee. Provides that in prosecution for possession of firearm in or on public building subject to such policy, ordinance or regulation, concealed handgun licensee affirmative defense is not complete defense, but results in Class A misdemeanor conviction punishable by 364 days' imprisonment, $6,250 fine, or both. ] Prohibits person from transferring certain firearms to recipient person knows, or reasonably should know, is under 21 years of age. Punishes by maximum of 364 days' imprisonment, $6,250 fine, or both. Specifies exceptions. ] Appropriates moneys to Department of State Police for implementation of Act. Declares emergency, effective on passage.