that you seek max velocity, with very light bullets, in something like the .45 Super. I'm interested in seeing if the Mach II+ claims of the RBCD people are realistic or not. I dont care if the factory loads make the grade or not. I just want to know if it's feasible to do at all. Given fully-supported barrels, thick-webbed brass, heavy springs, neoprene recoil buffers, perhaps even a longer than normal barrel, rifle primers, Duplex powder charges, maybe even the .460 Rowland case, hollowbased bullets (like the THV Arcane, 60 gr .45 ACP, which claimed 2200+ fps, etc. What powders would you start with? Any tricks of the trade? I"d be willing to handlap barrels, do "Paradox" rifling, taper the bores, whatever.

Try a paper patched round ball in a 77/44...the Chrony said a hair over 2400 fps but I don't know where it landed.

Just get a 454 casull and be done with it.

1ad12,
Look carefully at the barrel you are considering, the pressures that you want to generate and the weapon that is supposed to withstand all of this and stay together without any kind of failure. Now consider that velocity requires powder space. The more volume you have the faster you can drive a bullet. The more volume you have the slower the burn rate that is efficient in the cartridge. As volume goes up the lighter bullets get left behind because they do not provide resistance enough for slow burning powders and they don't withstand higher velocities well. (there are exceptions). A case with thicker walls adds only slightly to the pressure resistance of a round in the chamber and detracts severely from it's powder capacity - you loose much more than you gain. You cannot safely make a small case meet velocities of a larger case. Duplex loads are the MOST DANGEROUS practice that remains from the days when powder selections were not available with the wide range of burn rates that we have today. Tapered bores do not stabilize bullets well. If you want super velocity then you can get that with a loose barrel but it will not be accurate and all the velocity in the world does no good if you can't hit a target.
Select the right cartridge for the job you intend to do and work within the limits of that cartridge. If you have to run duplex loads, taper the bore, lap the barrel to loosen it up and use "special" shells to attain velocity then you are simply using the wrong ammo.
PaulS