A firearm is generally a rifle, pistol, shotgun, or other portable weapon that expels a projectile (bullet) by use of an explosive action. The definition of a firearm may vary from state to state under state statutes—and under federal statutes—and related items such as a muffler or silencer may be included in the definition of a firearm for purposes of certain criminal offenses (crimes).
In Pennsylvania, a firearm is defined under state law as any pistol or revolver with a barrel length less than 15 inches, any shotgun with a barrel length less than 18 inches, any rifle with a barrel length less than 16 inches, or any pistol, revolver, rifle or shotgun with an overall length less than 26 inches. The state also includes any firearms which are not detectable by X-ray machines or metal detectors as part of the definition. Additionally, items such as mufflers or silencers are considered firearms themselves when they are intended for use with a firearm. Federal law also has its own definitions and regulations regarding firearms, which include similar criteria for what constitutes a firearm, and also regulate the possession and transfer of firearms and related items like silencers. It's important to note that both state and federal laws regarding firearms are subject to change, and individuals must comply with both sets of laws.