I know this to be true through what I've read in the past but I'm looking for something specific that makes this the case. In New York, they don't define pistol in penal code 265, although they do define rifle and shotgun. This then defaults to the federal definition which does exist. By what process does this happen? What law says that because the state lacks a definition, the federal one is now in force? Anyone know specifically?  I'm trying to give a solid answer to this on another forum but I want to get it right. Thanks.

In NYS, a "firearm" defines a pistol, revolver, SBR, SBS.

In the list of things defined as a firearm, a) is a pistol.  Unlike shotguns and rifles which have their own definition, pistols don't. From what I was able to gather, the Supremacy clause of the Constitution accomplishes what I'm thinking about. Where a state doesn't further define or restrict something, federal law is supreme.

Is there some confusion in your mind over what constitutes a pistol?

This has been asked previously on other NYS gun forums

http://nyfirearms.com/forums/laws-politics-firearms-self-defense-weapons/96171-nys-legal-definition-pistol-handgun.html

I am not a lawyer, so I may have no idea what I am talking about, but ...

Isn’t New York a Common Law state?  If something is not addressed in the criminal statutes, then previous court precedents (decisions) will govern.  How have the courts in New York previously defined a pistol?

There is no general legal principle such as you're describing--i.e., that if state law is silent on a definitional question, that a definition of that term in federal law is controlling for the purposes of state law.  If New York has failed to define the term "pistol", and that definition matters, it's nearly certain that case law will have addressed it, and may have applied the federal definition for any number of reasons.  Or case law may have defined the term differently--there's no reason they would have to follow the federal definition.

From a thread awhile ago, I remember one of the lawyers chiming in that the Federal definition has absolutely zero relevance.  In the absence of a state definition, the commonly accepted dictionary definition  is used.

We have a similar problem in Texas & maybe Oklahoma w/ the definition of shotgun, OP, which may prevent Mossberg from selling their 14" 12 ga firearm here.