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Joined: Jan 2002
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Sidelock
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Sidelock
Joined: Jan 2002
Posts: 11,548 Likes: 158 |
From everything I've read here (and elsewhere) in numerous discussions of proof, I would have said no. However, someone recently brought the following quote to my attention, from McIntosh and Trevallion's "Shotgun Technicana", p. 78:
"English proof law holds that deepening a chamber renders a gun out of proof, but simply lengthening a forcing cone does not. (Or at least this is the London Proofmaster's position; we're told the Birmingham Proof House does not permit forcing cone alterations.)"
Based on the above, a friend who recently had forcing cones lengthened on a vintage British double emailed the Birmingham Proof House. He received the following as part of a brief reply from the assistant proof master:
"The gun would be out of proof by removing material from the forcing cone."
Mr. Trevallion, Dig, Hugh, others familiar with British proof practices . . . have we been wrong all along when stating that lengthening cones does not invalidate proof? And since there is no standard length for forcing cones (unlike chambers), and since there is no proofmark specifically relative to the forcing cone, how would the proofhouse know for certain that the cone had been modified?
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Joined: May 2004
Posts: 616 Likes: 1
Sidelock
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Sidelock
Joined: May 2004
Posts: 616 Likes: 1 |
From everything I've read here (and elsewhere) in numerous discussions of proof, I would have said no. However, someone recently brought the following quote to my attention, from McIntosh and Trevallion's "Shotgun Technicana", p. 78:
"English proof law holds that deepening a chamber renders a gun out of proof, but simply lengthening a forcing cone does not. (Or at least this is the London Proofmaster's position; we're told the Birmingham Proof House does not permit forcing cone alterations.)"
Based on the above, a friend who recently had forcing cones lengthened on a vintage British double emailed the Birmingham Proof House. He received the following as part of a brief reply from the assistant proof master:
"The gun would be out of proof by removing material from the forcing cone."
Mr. Trevallion, Dig, Hugh, others familiar with British proof practices . . . have we been wrong all along when stating that lengthening cones does not invalidate proof? And since there is no standard length for forcing cones (unlike chambers), and since there is no proofmark specifically relative to the forcing cone, how would the proofhouse know for certain that the cone had been modified? That would be my same question, how would they ever know if its been modified?
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Joined: Feb 2004
Posts: 13,880 Likes: 16
Sidelock
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Sidelock
Joined: Feb 2004
Posts: 13,880 Likes: 16 |
Even if the gun were sent back for proof, is there a marking that indicates that cones of any specific length were proofed?
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Joined: Apr 2005
Posts: 1,696 Likes: 46
Sidelock
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Sidelock
Joined: Apr 2005
Posts: 1,696 Likes: 46 |
When forcing cone lengthening became fashionable here about 1988 or there abouts it was very common practice for gunshops and gunsmiths to advertise this work and to carry it out often on a while you wait process.
Indeed GMK the British Beretta importers used to have their resident gunsmith Gordon Swatton doing it at Game Fairs and competitions such as the British & English Opens.
It did not contravene Proof House regulations, maybe times have changed and Birmingham have bullied their way into the scenario.
It is typically a cock up, because Proof Law clearly says that if you alter a proved barrel in any way it renders it out of proof. That is why you have to have it reproved if you multichoke a fixed barrel.
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Joined: May 2010
Posts: 1,537 Likes: 100
Sidelock
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Sidelock
Joined: May 2010
Posts: 1,537 Likes: 100 |
It has always been my understanding that lengthening a chamber cone SHOULD render a gun out of proof as there is metal removed from the barrel . But came the argument ,providing the actual chamber has not been lenghtend byond the proof limits how dose any one know it has been done ?So it was not a consideration and as no directive was issued no one bothered .But Proof law is fickle, CIP has changed thinking in some areas. for instance I have threaded dozens of .22LR barrels to take moderators with out any problem ,Then a few years back it was decided that "as this could subsancialy weaken a barrel" these guns are now out of proof . This has been argued but to my knowlage no test case has been defined .
With proof we are at the discretion and mercy of the proof masters to some degree and often new proof masters make new policy . The answer to the original question must be yes it dose as a technical point but a point that has never been enforced .
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Joined: Jan 2002
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Sidelock
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Sidelock
Joined: Jan 2002
Posts: 11,548 Likes: 158 |
Seems to me that certain alterations in a barrel do not impact proof. Honing/lapping, for example, as long as the bore diameter remains within the parameters for that particular bore (not more than .010 larger than standard). Likewise, I'd never heard that opening chokes impacted proof, although both Dig in his book "Vintage Guns" and Salopian above refer to a gun requiring reproof if it's altered to accept choke tubes. In the latter case, significantly more metal has to be removed to accept screw-in chokes than is the case if a gunsmith simply removes a few thousandths to open a fixed choke. Thus, requiring reproof in that case would seem more logical.
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Joined: May 2010
Posts: 1,537 Likes: 100
Sidelock
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Sidelock
Joined: May 2010
Posts: 1,537 Likes: 100 |
The key words are "substantially" reducing the strength of the barrel as fitting a multi choke boring out to cylinder dose not effect the overall integral strength of a barrel .British proof can be a mine field ,even those of us that are involved with regularly submitting guns get confused with 8[?] changes in proof law and stamps in the last 100 years .No wonder we can not keep up .Personally I think its time we started from scratch again ,but that's not going to happen so we just muddle along as best we can hopping we get it right most of the time.
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Joined: Jul 2006
Posts: 1,164 Likes: 11
Sidelock
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Sidelock
Joined: Jul 2006
Posts: 1,164 Likes: 11 |
L.Brown,
Lengthening the forcing cone results in a more gradual angle of transition between the chamber diameter and the bore.A more gradual transition between chamber and barrel diameters will result in a reduction in stress concentration in the barrel wall.In my opinion, lengthening the forcing cone will almost certainley increase the ultimate strength of a sound, in proof barrel.
One would think the Birmingham proof house would want to confirm the impact of lengthening forcing cones on barrel strength before making any ruling on the issue.
Roy Hebbes
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Sidelock
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Sidelock
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Joined: Feb 2004
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Sidelock
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Sidelock
Joined: Feb 2004
Posts: 13,880 Likes: 16 |
Too many variables to say the effect is this or that. I have cut 3/4", 1 1/2", and 3" forcing cones in 12ga. What angle is on the outside and the forcing cone angle together with the chamber depth relative to the outside taper all play into the equation.
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