Nitro Reproved - Safe or Unsafe to shoot

[fino]

Hi all,

Anyone who follows gun auctions is used to read on the gun description the expression "x inch nitro reproved barrels". Generally you can read that on guns that seem to be the best deals (e.g., Purdeys or Hollands with estimated hammer prices of £ 5.000 or even less). Off course that when you read that expression and then go check the bore/wall thickness chart most of the times you will find that a significant amount of metal has come off of the barrel, which explains why the barrels went back to the Proof House, where they were "nitro reproved".

However I would like to put the question in a more practical level, does the expression "nitro reproved" should be seen as a warning to not to shoot the gun that way described with modern nitro powder under any circumstances because it is unsafe to do so, or providing that you pay attention to charges it is safe for someone to use modern cartridges and actually shoot the gun?

As a personal testimony (and please note that this is not an advice!!) I can tell you that I used to own a W&C Scott live pigeon sidelock, chambered for 2 ¾ cartridges, with 2 sets of barrels. One set was choked 7/8-full and was as new. The other barrels set was choked 3/8-3/4 and the bores measured .18-.19 thou. This was the barrel set I used more often and I can tell you that I literally fired several hundreds (at least) of modern cartridges rounds with them shooting pigeons, partridges and ducks, most of the times with loads of 34 gms, but sometimes even with 36gms. Never had an accident nor felt unsafe. Maybe I was just lucky, who knows…

In any case I see a shotgun as an object with a purpuse, which obviously is to shoot. Would you discourage me to shoot a potential "nitro reproved" shotgun as the above mentioned W&C Scott?

Looking forward to read your comments,

Regards all.

[zanes]

Depends entirely on condition and if it was reproofed last week or eighty years ago.

[fino]

Zanes, thank you for your comment, but I was talking about "nitro reproved" guns, not reproofed.

Unless I've missinterpreted the expression "nitro reproved", I took it as a case of a gun that went back to the Proof House but was not found fit enough to pass a nitro proof test.

[zanes]

Hmmm. I'm now confused somewhat!

Someone who knows what they're on about (and can explain the meaning of nitro reproved to me!) will be along soon enough I suspect! :P

I'd always thought "nitro reproved" was just a grammatically correct contraction of "was submitted and passed the proof test for nitro powder".

[Kungfugerbil]

Unless I've missinterpreted the expression "nitro reproved", I took it as a case of a gun that went back to the Proof House but was not found fit enough to pass a nitro proof test.

I think you have misinterpreted it.

Reproved is a typo or mis-spelling. If it had gone back and failed proof on nitro it would either be re proofed for BP only or rectified. Or scrapped depending on quite how it had failed proof... :)

[TattooedGun]

I understood reproved to mean it had been re-proofed.

Nitro Reproved means it was originally proofed for BP, and it had been re-proven (proofed) for Nitro Base powders.

[fino]

Unless I've missinterpreted the expression "nitro reproved", I took it as a case of a gun that went back to the Proof House but was not found fit enough to pass a nitro proof test.

I think you have misinterpreted it.

Reproved is a typo or mis-spelling. If it had gone back and failed proof on nitro it would either be re proofed for BP only or rectified. Or scrapped depending on quite how it had failed proof... :)

Hi Kungfugerbil,

Thank you for you comment, that changes everything, I really had a different idea. Besides here in Portugal rules are not so strict as in UK regarding guns going out of proof and so that together with a language issue really put me out off context .

So considering what you said we could say that a gun recently "nitro reproved" with wall barrels thickness of .18-.19 can be seen as a full functional gun. I think I'll start paying even more attention to gun auctions .

BR

[Kungfugerbil]

..we could say that a gun recently "nitro reproved" with wall barrels thickness of .18-.19 can be seen as a full functional gun

I would have no hesitation shooting a gun that had recently been nitro re proofed (or proved, or proven!) over here. Of course, if it were of uncertain origin I would most certainly send it for a health check wih my local friendly workshop. I would also do that if it were of any significant value.

[Robert303]

Nitro re proofeed is normally found on older guns that had originally just been proofed for Blackpowder cartridges. So they were safe to use with Nitro cartridges AT that TIME. After that it will depend on how often the gun has been fired and what the the barrel wall thickness is. I cannot remember the minimum wall thickness at the moment but am sure others can tell you. I did read this somewhere but cannot swear it is accurate. While no substitute for an actual proof test, a useful rule of thumb states that the minimum barrel wall thickness should be .020" in a 12 gauge gun. I also found this on the web some years ago. I do not know the source or how accurate it is.

The question often is asked, "What are the minimum barrel thickness to safely shoot my gun?" and its a difficult question to answer without risk. An answer, without a close inspection of the barrel condition, is impossible without risk of being wrong.
The use of black powder and corrosive primers is a primary cause of pitting in some old shotgun barrels, especially if they were not cared for properly shortly after their use. The results can be anything from slight to severe pitting and those pits effectively reduce the barrels thickness by the pits depth at that location. If the shotgun bore is not mirror bright, a competent gunsmith will determine the depth of the pitting and take that into consideration when measuring barrel wall thickness for safety.
With that said, here is a general 12 ga. guideline:
In the forward 2/3 of the barrels length, a thickness of .025" has been suggested as a minimum thickness for safety reasons. The rear 1/3 length of the barrels, where the maximum pressures are exerted, requires thicker wall thickness. The wall thickness at the juncture of the chambers and the forcing cone is the most critical and is where it has the highest pressure exerted.
With some uncertainty, its assumed that a thickness of .090" at this juncture location would be about minimum.
UK Working Standards recommended minimum wall thickness measured 18" from the barrel breech from Double Gun Classics p. 56, Vol. 1, No. 4 Jan-Feb, 2006:

2 1/2" 12g- .028
2 3/4" 12g- .032
Re-proof recommended minimum- .024

And, The Hunter's Encyclopedia from the German proof house: minimal wall thickness at end of chamber, regardless of length, for 12, 16 & 20 gauge guns should be 2.3mm (.0906") for 'ordinary good steel' or 2.1mm (.0827") if a 'Special Steel' was used. For the 24 & 28 gauges, due to their higher pressures, 2.4mm (.0945") was recommended.
Minimal wall of .6mm (.0236") was recommended in the "forward third" of the barrel.
There is greater pressure as the gauges go from 12 to 16 to 20 etc. therefore the minimum values might increase.
Learning the measurement of known original Parker barrels of the same gauge would be a good example to use to understand what Parker thought were safe values in the days when they were making shotgun. The problem with this method is finding "original" Parker barrels and getting permission to take measurements.
The thickness of the barrel depends primarily on the frame size with respect to gauge, and secondarily on length. The barrels were finished by longitudinal hand filing to fit a general set of outside diameter checks. The filing was generally done to balance the gun at the hinge, but it could be muzzle heavy or light if the customer ordered. The longitudinal hand filing produced barrels that were not necessarily concentric with the bore, and wall thickness can vary side to side or top to bottom. There is no standard thickness.
Some guns appear to have thick barrels because full choke barrel muzzles are .040 or more thicker than the bore.
Again, without a hands on inspection, these numbers mean little; don't risk life and limb shooting bad barrels. Have them inspected by a competent and knowledgeable gunsmith before shooting an older gun of unknown history or condition.
Here is a link to a video that demonstrates how barrel wall thickness is tested.

[fino]

Thank you Robert, great explanation! Acording to what you said I believe it is fair to conclude that before biding for/buying a reproved gun it is wise to know when was the gun reproved (although in manny cases that information is provided by auction house/dealer)

So my next question would be if the reproved punches by any way state the year that the gun was reproved. Do you know anything regarding that?

Regards