
Testing Methods Used in the Proof of Firearms 



Viewing... When a firearm is submitted for Proof the first stage of the procedure is known as "viewing". A weapon which does not satisfy the Proof House viewers is ruled not to be in a fit condition for rest of the Proof process.
The viewing procedure is as follows:
The weapon is classified, i.e., it is allocated to one of the four classes.
It is visually inspected for defects and the straightness of the barrel(s) is checked.
Weapons of the first class and long barrelled weapons of the 4th class are bore gauged at 9 inches from the breech face and the bore diameter is taken as that corresponding to the largest gauge which will enter to that point. If the diameter does not lie within prescribed limits the arm is rejected.
Measurements are taken of chamber dimensions, as given in the diagram below:
each of which must lie within prescribed limits. The dimensions quoted in the "Rules of Proof" are for finished chambers. To allow for polishing after Proof the minimum figures of dimensions A, B or C are read as if they were 0.003" less.
Weapons of the 2nd and 3rd classes are also gauged. The length of the chamber, each diameter of the chamber(s) of the barrel(s) and in a revolver each chamber of the cylinder must lie within the prescribed limits.
Weapons of 4th class present a number of problems due to the wide variety of weapons involved. These can range from a muzzle loading punt gun to a humane killer. In general smooth bore barrels are gauged 9 inches from the breech face to determine the bore diameter, but if the barrel is less than 9 inches long it is gauged at the muzzle.
The final procedure of "viewing" is a further inspection and further gauging after the Proof Load has been fired. If visual inspection reveals a defect or if gauging shows expansion beyond the dimensions permitted the weapon is condemned.
Proof Firing... The purpose of a proof load is to subject the chamber and barrel to a pressure which exceeds that which will be encountered in normal use. Similarly the action face, or in the case of a bolt closure, the bolt face, experiences a pressure in excess of that normally met. There are two distinct safety effects of this procedure.
First if the barrel or chamber is weak or flawed, the excess pressure will reveal that fact under controlled and "safe" conditions rather than have a failure or accident occur in the field.
Secondly, the application of excess pressure places the material of the chamber and barrel in compression.
Originated... 18 December 2002, New Domain... 13 February 2004, Upgraded... 26 January 2007,
