doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Proof house marking vs: bore size question

To my mind one only has to ask why would a barrel maker in Birmingham and London spend time enlarging a barrel's bore diameter greater than the standard to which all the gunmaker's worked to; or for that case bore and finish the barrel's bore diameter less than the standard? Two reasons come to mind, and those are the barrel maker is getting paid to do it because a gunmaker's customer desires it; and secondly to correct a flaw in the barrel discovered during boring and finishing the barrel to standard (in this discussion we are using .729")

Removing more metal from the bore of the barrel costs the barrel maker more and he is getting paid for making the barrel to standard, going larger results in less profit for him. It therefore seems within reason to assume that as soon as the barrel maker measured that he was where he should be in the bore diameter lapping to "standard" he stopped and polished the bores and send the barrel set on.

Just because the proof house may have had primitive barrel bore measuring devices that they were required to have under the rules of proof for the period of time does not mean that the barrels makers did not have accurate incremental measuring devices. Accordingly, we cannot assume that the proof houses did not have bore measuring devices which could measure the bore in .001" increments, since micrometers were invented in the 1800's. However they were required to use the mandrels to measure the barrel's bore to meet the proof laws at the time, as the following quotes from the 1954 UK Rules of Proof demonstrates.

The following is directly from "Rule 18" of the 1954 UK Rules of Proof, page 8: .....(a) As to an Arm of the First Class---- (according to p.3 SCHEDULE B arms of the "first class" are "smooth bore breech loading arms of 4 bore or smaller discharging shot or bullet"....) "Each barrel shall be gauged at a distance of 9 inches from its breech face for its bore diameter which shall be within the limits set out in Table 1 of Appendix III for the diameter of such barrel (this Table shows that 12 bore guns can have bore diameters of a min of .710" to max of .751" diameters). The bore gauges to be used shall be of the diameters set out in Table 2 of Appendix III(This table delineates for the 12 bore .710", .719", .729", and .740" diameters of bore). Such bore diameter shall be deemed to be that of the largest bore gauge which will enter the barrel to a depth of 9 inches from the barrel breech".

It is evident from reading the above that a shotgun barrel could have measured a max of .729" at 9 inches from the breech and the bore could have measured much larger at 9 1/2" (or wherever along the barrel length) from the breech and meet the 1954 Rules of Proof. I suspect that from time to time this was encountered and the two proof houses had the incremental measuring devices to measure to measure such differences for the full length of the barrels bore.

In today's world of gun manufacturing where measuring a gun bore diameter easily and throughout the barrel, these 1954 rules may be seen as crude, but they worked. The Proof Master and his men had keen eyes and they denied proof many times on the basis of their visual examination.

I don't know what it measures. I was just agreeing the proof says it is exactly the nominal 16ga measurement...Geo

Bushveld, I think you underestimate the magnitude of concentricity problems.
The technology to address that economically seems to be fairly recent.

I'll survey the safe and report back.

Meanwhile has anyone actually tried asking the Proof House?

Jeremy

ClapperZ;

Thank you for your comment.

However, I was not considering the concentric bore versus out diameter of the barrels(such as Holland's has focused upon and corrected in its barrel making) but was stating how the barrel's bore id could be changed beyond the 9 inch standard position for measuring. Such a bore diameter issue could arise for instance from an ill advised "gunsmith" taking too much bore away after hammering out a deep dent into the barrels, but the barrel was still in proof.

However, the wall thickness gauges and inside bore gauge technology existed before the 1954 proof rules, i.e. the electric power steam tubine generation industry in measuring condenser tube wear for one example; and which England via Parsons turbines led the world from about 1900.

My own English made barrel bore gauge must go back to the 1960's.

Maybe Hugh Lomas could shed some additional light on the age of the technology as I remember Jack Rowe saying that Hugh was educated and trained as an Engineer in the UK, before he came to America as an Engineer. I also remember Jack having a very very high regard for Hugh and his gunsmithing. I wish Jack was still here to guide us in this discussion.

One of Jack Rowe's career time frame fellow gunsmith, Malcolm Cruxton of Price St. Birmingham is still living and working in his Price St. workshop. I may send him and e-mail and see what he can tell me about the subject. He was going to Thailand for the Christmas holidays and beyond; and he has likely returned to Birmingham by now.

I have a few photographs of a sampling from my collection showing some with metric proof markings which range from 18.3 to 19.1 showing the decimal metric progression. I'm trying to figure out how this forum works for image posting. I'll add them when I do.

Jeremy

Eureka! As the old Greek exclaimed. I found the answer, while looking for something else. In Vic Venters' "Gun Craft" article in Shooting Sportsman, Mar/Apr 2012:

"For example, under the old Imperial-era Rules (1954-89 "tons" era), a gun could remain in proof so long as its bore was enlarged no more than .010". By contrast, guns proofed under the 1989 CIP Rules (and those that have followed) remain in proof through enlargements up to 2mm--which is equivalent to .008".

I think either Vic or the copy editor mislaid a decimal point in that quote. Should be 0.2mm equivalent to .008". So the new metric measurements still allow some "slop"--just not quite as much. It could start life marked 18.5mm (the standard) and have been enlarged up to 18.7mm without requiring reproof and remarking.

Don't forget that the Gunmaker may just polish the barrels out a little when the gun comes back from proof without taking the gun out of proof for the purpose of regulating the gun to shoot a particular cartridge to obtain optimum patterns. Usually on the higher end guns when a customer orders a gun to say shoot 50% patterns at 40 yards with say Eley Grand Prix 30 gram 6 shot. Lagopus.....

As I see it then the change from simply marking the bore as 12 to .729 actually accomplished Nothing. My understanding was that a bore marked 12 was in proof until it would accept the 12/1 gage (.740"). Under the .010" rule the .729 mar4k3ed bor would be in proof until it accepted a .739" gage while under the .008" rule it would go out of proof when it accepted a .737" gage.
In any case the gun could have been proofed with a bore diameter of .736" & would go out of proof (Depending upon the rule it was proofed under) with .001", .003" or .006" enlargement.
I guess I had been mis-led down through the years but I had thought the reason for the change to the decimal marking was to allow a given amount of enlargement from the "Actual" proof diameter rather than from a "Nominal" diameter.
I have seen "Continental" guns marked in metrics which for a nominal 12 gauge carried a marking other than 18.5mm or 16.8mm for a 16 gauge. Apparently They got it right & marked the actual measured diameter & then give you that constant 0.2mm leeway for honing.

I have a lovely pre-war Simson 16 that I purchased knowing it had been honed out of proof but had plenty of meat in the barrels and was still safe, bores measuring 0.674, both sides.

This thread made me take a second look and since the barrels are stamped 16/1, which according to Dig's website is 0.669-0.678, I'm still in proof.

I'll go by the rules in effect at manufacture.