You're correct, Miller, in stating that Bell and Armbrust did not lengthen the chamber to 3" to get "normal" readings on the 3" reloads they tested. However, Bell did not describe the reloads as "low pressure". In fact, he described the lighter of the two as "too hot" for another test he had planned, and "scheduled for dismantling". The other one, even hotter, did come close to producing Roster's jump of 1500 psi--but that was when fired in a 2 1/2" chamber. I don't think any of us are nutty enough to shove a 3" shell into a short-chambered gun, at least not intentionally!
