A person can buy a used Beretta 84 gun frame through websites like Gunbroker or at local gun shops. The frame is the main component of the gun where other parts are attached.
A homophone for a large frame could be "a full frame."
The frame.
It is the frame of the gun. With present day guns, the part with the serial number on it.
It is not a large frame.
The receiver is the frame of the gun. When a gun is marked with a serial number, it is stamped on the receiver. It will be a different part depending on the type of gun.
On the frame and or barrel
The serial number is on the frame.
You will have to specifiy if it is a handgun, rifle or shotgun.
Gun shop, gun show, want ad
Normally on the frame/barrel/receiver
It is in different places depending on the gun, but typically, it will be somewhere on the barrel or on the lower frame of the gun.