On a lot of the pressure data I've seen give BP pressures in LUP. I don't know the correlation to CUP or PSI, but I do know the they were a lot less powerful than what you see now. I think current pressure of 11K would be a magnum load from the BP era for a revolver cartridge IMO.
Try this link for an interesting read:
www.tapatalk.com/groups/britishmilitariaforums/fiocchi-ammo-in-a-mk-i-t10995.htmlI for one would not trust smokeless loads for an number of these early guns as I watched a collector friend try an old Bulldog revolver in 450 with Fiocchi ammo (after I told him "I wouldn't try that")....... he cracked a cylinder on the first shot.
Fiocchi's .45 Corto ammo is famous for blowing up antiques; people who shoot these guns only buy Fiocchi to pull the bullets and replace the powder with a more suitable load, either BP or smokeless.
I've done a lot of research on BP and Smokeless, and there are two main reasons for the lore that smokeless is unsafe in BP guns- early home reloaders and gun companies.
Early home reloaders had a tendency to load the new smokeless powder by volume rather than weight- which, naturally, damaged their guns. This led to powder manufacturer's putting warnings right in their catalogues about this. This also led to gun companies creating 'new' versions of their guns that were 'proofed for smokeless.' A classic example of this was Iver Johnson. Their 1st and 2nd model top-breaks were from the BP era. In 1909 IJ came out with the 3rd models, and made much of the fact that they were 'proofed for smokeless.' They still had huge stocks of parts for the 2nd model, so they created the trade brand 'US Revolver Company' and kept right on producing a variation of the 2nd Model using old barrels, cylinders and frames. The big deal about these USR guns? They were an economy gun that was... wait for it... proofed for smokeless! Um... And what was Iver Johnson telling people at the time? "You need to buy our new guns to shoot smokeless ammo... it's not safe in the old guns!" All the while still making the old guns under the new brand and saying they were safe for smokeless.
Smell anything fishy here, perhaps?
A European friend on mine in who was brought up the gun trade is very familiar with European proof houses, and says they nitro-proof BP cartridge firearms all the time- as well as damascus shotguns. (European shotgunners think we're nuts for not shooting our damascus shotguns. They do it all the time, without incident.)
As to the Webley, the Brits switched to smokeless ammo only a few years after this gun was introduced, and shot it through these guns for the next forty years without apparent ill effect. What people seem to forget is that when smokeless cartridges were introduced
every old gun was a 'Black Powder' gun, and the new smokeless loads were formulated to work in these existing guns. They did so just fine, thanks. In the last decade or so scientific testing had shown that many smokeless powders, especially the older ones, mimic both the chamber and down-bore pressures of Black Powder when loaded with the same weight of projectile to the same velocity. Red Dot was extensively tested in Shotguns and the difference between it and black powder was within the statistical margin of error.
That being said- .455 Ely- which the Webley Mk.1 was originally chambered in- is rated at 13,400- 15,000 CUP depending on whom you talk to. Commercial .45 ACP runs 19,000-21,000 CUP. It is a bad idea to feed these old guns factory .45 ACP. It
usually doesn't blow them up, but it will give them a case of 'Wobbley Webley' syndrome... and sometimes it
does blow them up. The .45 ACP load I am using is a bit lighter than many of the loads recommended for these guns and is supposed to be making about 13,500 CUP. It's actually lower pressure than the British military load that was shot through these guns for decades; that one tested at about 15,000 CUP.
Any good quality gun in good condition can use
the correct smokeless load. I don't hesitate to fire these guns with my smokeless handloads, but there is a huge caveat there- I stick to light loads (because there is no point in beating a nice old gun to death... or blowing it up.) The other is that I have done a lot of research and spoken to a lot of other people about their experiences, experiments and tests. If you haven't it's probably best to stick to BP or Trail Boss- they are fairly fool-proof if you follow the directions.
It's really a good idea to use mild loads in any antique firearm; the materials were often not as good as their modern equivalent, and mild loads will prolong their working life.