Yes, those numbers are Burrard's conversion.
The long explanation starts just past 1/2 way down here Frank
https://docs.google.com/document/d/1...UOZEFU/preview
Here's the short version for us non-deep thinkin' types
Burrard's conversion formula for Tons/sq. inch as measured by LUP is probably close to modern piezo transducer measured Pounds/sq. inch (PSI).
Since we cannot KNOW the conversion for PSI as measured by LUP to PSI as measured by transducers, adding 10 - 14% to the load pressures reported as PSI by LUP seems reasonable.
In a 1927 Western Cartridge Co. flyer “Super-X The Long Range Load” by Capt. Chas. Askins the 12g “Duck Load” (not specified but presumed to be 1 1/4 oz. Super-X “Field”) is described as 3 1/2 dram (38.5 gr. Powder; also not specified but no doubt DuPont Oval) at 1400 fps (at the muzzle rather than 3 feet) and 1000 fps at 40 yards, with a breech pressure of 3 3/4 tons or about 11,480 psi by Burrard’s conversion.
All of Coxe's pressure curves are in the doc also.