doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Thomas Bland BLE proof marks

Clean, uncluttered, easy to decipher:





Which if I did this right, puts it 1954 to 1989:



...I'm being told 1955 manufacture.

...but I get 1963 from this proof date:

Drew do you have a conversion factor for British Tons to PSI? I calculated for 3-1/4 T using a factor derived from an earlier post of yours which referenced Development of proof (loads) including the US. The Calculation came out to just under 10,400 PSI.

Geoff: I agree the Birmingham date code is 'O' for 1963

Mike: it's complicated
Pressures can be converted to modern piezo transducer numbers using Burrard’s formula if originally expressed as (Long) Tons/Sq. Inch by LUP (Lead [Crusher] Units of Pressure), or by adding 10-14% if expressed as PSI by LUP.
Burrard’s estimated Long Tons/ Sq. Inch Lead Crusher Pressure (Cp) conversion to PSI (pound-force per square inch): (Cp x 1.5) - .5 = TSI, TSI X 2240 = PSI.

“Highest Mean Service Pressure” equivalent PSI transducer values as converted from LUP by Burrard’s formula:
2 tons/sq. inch (NOT 2 X 2240) = 5,600 psi (pounds/sq. inch) = 386 BAR
2 1/2 tons = 7,280 psi = 502 BAR
2 3/4 tons = 8,120 psi = 560 BAR
3 tons = 8,960 psi = 618 BAR
3 1/4 tons = 9,800 psi = 676 BAR
3 1/2 tons = 10,640 psi = 734 BAR
3 3/4 tons = 11,480 psi = 792 BAR (The SAAMI maximum for 2 3/4” 12g is 11,500 psi)
4 tons = 12,320 psi = 850 BAR

Since we Colonials aren't good at math the Master of the Birmingham Proof House told Larry Brown to simply use Tons x 2240 x 1.33 to convert Tons to Piezo numbers
2” chamber / 2 3/4 tons = 8,193 psi
2 1/2” chamber / 3 tons = 8,938 psi
2 3/4” chamber / 3 1/4 tons = 9,682 psi
3” chamber / 3 1/2 tons = 10,427 psi
3” chamber “Magnum” / 4 tons = 11,917 psi

Good stuff from John Brindle, author of Shotgun Shooting: Techniques & Technology published a review of Proof and Service pressures in Part 5 of his series in The Double Gun Journal, “Black Powder & Smokeless, Damascus & Steel”; Volume 5, Issue 3, 1994, “Some Modern Fallacies Part 5”, p. 11.
His estimated post-1954 but pre-CIP standard pressures by LUP converted to piezo transducer PSI
......................Standard Service... Max. Service.....Proof
12g 2 1/2”.........6,800 psi.............8,800 psi.........12,250 psi
12g 2 3/4”.........7,800 psi.............9,800 psi.........14,050 psi
(CIP 2 3/4”).......10,733 psi............12,328 psi........13,489 psi

Good stuff! Copied and pasted into my "Gun stuff" document.

...how'd I do on deciphering the proofs on the Bland?

...trying to get better at this and looking for feedback.

Geoff, in the enlarged photo with the .719" and halberds if the marks in the crossed halberds is "O C" then the barrels were proofed in 1988 (the letters are somewhat fuzzy in the photo).



Birmingham Date Codes

I'm pretty sure it's a O and B...but it'd be great if it were an O and a C.

I'll have to wait until it gets here to be able to look at it better.

It seems strange to have 1 barrel .729 and the other .719 but I have a theory, based on having owned several Britt boxlock waterfowlers. At the time some of these guns were made shells with felt wads were used and the gunmaker wanted to insure combustion and perhaps increase performance by having tighter constriction in the barrel.

Usually, when I see a difference in bore measurements like that, I think the worst, but, it appears this gun was proofed that way. Nice to find an English gun with 2 3/4” proofs at 3 1/4 tons.

Best,
Ted

I would be quite interested to know, since I don't
After 1887 the bore was marked based on using a plug gauge measuring at 9". If the plug gauge of .729 couldn't pass, the barrels were marked 13/1 but could be .719" to .728"
The bore was marked in inches starting in 1954 but IS THAT THE ACTUAL MEASUREMENT or was the plug gauge still used? Could .719 still be up to .728"?
After 1989 the bore was marked in mm (18.5 = 0.728)

Given the manufacture date of - I think - 1963, do you think that's still a possibility?

Felt wads were never passé in Europe. The last pallet of Eley 16 gauge I bought was felt wads, VIP was the load, if I remember correctly. Purchased early 2000s.

‘Course, they might be, now. But 1963, no way.

Best,
Ted

OK. Found several sources stating "A significant change in 1954 was the requirement to stamp the actual measured bore diameter on the barrel flats, not just the nominal gauge number."

That's good to know...and this gun is almost 100% guaranteed to be made post-1954.

Drew, could you explain these conversions?

I just plotted PSI against Tons and got a near perfect linear regression of PSI=3360.5*Tons +1121.1. So the regression does not fit well with the origin, but my real question is why is it not PSI = 2240*Tons?

And if I could put my tire gauge on the chamber and, assuming it had the range capability, what would it read relative to these numbers here (i.e., are these PSI numbers real PSI as in a car tire?