Miller, I can't tell you where to look in your copy of Burrard. I have only an extract, and he addresses the effects of compressing the hull in the cone about 5 paragraphs into his discussion entitled "Length of Cartridge": "If the mouth of the cartridge is compressed by being held in the chamber cone, the resistance to the initial movement of the shot charge will be greater and the pressure will be increased." Well, we know from the Bell test (cited earlier) that there was a significant increase in pressure when a hull extended well into a forcing cone. If that "squeezing" effect initially retards the acceleration, with the greater pressure building behind it, does it not make sense that the acceleration--once the "obstacle" (case mouth) is removed--will be greater? And could that not explain an accompanying increase in recoil?
You are correct in stating that neither Burrard nor Thomas nor Fergus give velocity figures. However, both Thomas and Fergus report the same visual evidence (blown case mouths) that Bell reported, when he also reported a significant pressure jump. Or are you doubting three separate reports of blown ends on cases? And if, in the case of Thomas and Fergus, they report the same visual evidence, why is it not possible that they also experienced significant increases in recoil? Just because they didn't measure velocity does not mean that it did not increase. Or, the increased recoil may have been due to the change in acceleration when the charge was finally released, with greater accompanying pressure.
Fergus describes his experience with British shells "approved for use in 2 1/2" guns" in a pre-1900 Westley Richards and in a Jeffery (also 2 1/2") from the 1930's. (The Westley, by the way, was stamped as having passed reproof some time after 1954.) In the former, blown end and "stiff recoil that caused me to stop and examime the discharged cartridge". Yet the gun performed fine with true 2 1/2" hulls.
Thomas is well aware of the same situation and comes to the same conclusion: On some guns with "exceptionally abrupt" cones, "the use of the longer case may give rise to objectionable, or at least enhanced, pressures." Same thing Burrard says, using very slightly different words--Burrard referring to the compression of the case mouth. (But how else is that going to happen, except in the forcing cone???) Thomas also verifies that the gun in question works fine with true 2 1/2" shells, whereas "with 2 3/4" cases, though designed for 2 1/2" chambers, it recoils unduly and makes his arm numb." And the crimps are blown off.
We already know that the pressure increase is real. All the authorities agree, and Bell's tests prove it--significantly so, when the case extends well into the forcing cone. We also know that the blown ends are real: Bell, Thomas and Fergus all report the same evidence. Bell was using a pressure gun, so he couldn't comment on recoil. Nor did he report velocity, other than to say--for all the tests he conducted--that "velocity of all loads remained essentially the same", without additional specifics. (I would've liked to see the velocity on that 3"er with the blown ends and the big pressure spike.) So perhaps the difference in acceleration resulted in the increased recoil--which, given that the other two pieces of evidence (pressure increase and blown ends) are measurable or observable, I believe really did increase. Why doubt the third effect when we know for certain that the other two happened, and they're being reported by the same people?
But hey, if you guys want, go ahead and continue telling people that any 2 3/4" hull loaded to the appropriate pressure will work just fine in any gun with a 2 1/2" chamber, regardless of differences in cone length and angle. For that matter, while you're at it, tell them to disregard it when they blow the ends off the hulls. And if they feel increased recoil . . . well, it's all in their heads.
