I don't have access to a pressure gun, but some speculation. I highly suspect that crimp depth may indeed have more effect on "Maximum" pressure than the length of cone, except in the case of a very short cone. Realize the greates portion of the initial rise comes before the shot actually is under way. As soon as the shot starts moving volume of the burning area is increased. The pressure is of course rising very rapidly, so takes a slight increase of volume to offset the rising pressure. consequently the peak occurs just after movement. Anything which retards initial movement of the load can have a serious input on pressure (too deep or tight crimp) As long as the loaded shell is shorter than chamber there is no increased restriction to intial opening of the crimp, thus little reason for max pressure to be increased. If you measured the "Curve" what would seem far more likely would be a slightrly slower falling off from the peak, rather than a raising of it. This would seem to be critical only in the case of a bbl wall which was extremely thin at the juncture of chamber & cone, normally the weakest link in the chain. It would definitely not be recommended to fire a shell where the loaded length exceeded chamber depth, so that the end of the hull is forcibly "Crammed" into the cone. This can have the effect of increasing difficulty of opening of the crimp & cause a drastic increase of peak pressure.
