Handgun as a firearm classification

When I bought my Glock, I was told by my FFL that there was only one part of the gun that was actually considered the 'firearm' (but I'm forgetful over a year later). My guess would be the firing pin is the part that classifies the gun as a firearm, without it, it wouldn't be considered a firearm. Can someone please clarify the law(s) specifically that indicate when a handgun is considered a firearm?

Thank you!

 

typically its the receiver that is considered a firearm. so for the glock i would imagine it would be the grip frame.

 

to expound- a barrel, firing pin, slide, magazines, etc can all be bought without any background check. they are more or less replacement parts. but you cant buy the receiver (grip frame) without going thru the legal rigamaroll because thats the part that is considered a firearm.

 

So if it is just the grip frame, would it be legal to create a frame that mimics the factory frame?

I was hoping it would not be the grip frame that would classify it as a firearm for my theory. But if that's the case, my idea will not work.

Thanks y'all

 

Yes it is legal, but, you must be licensed as a manufacturer of firearms and put a serial number on the frame. CCF makes Glock frames; http://www.ccfraceframes.com/options.php.

Oh, by the way, Glocks are striker fired, no traditional firing pin.