Quick Load is a centerfire program. In a conventional cartridge rifle, the bullet is jammed into the throat of the barrel. There is a very fast pressure rise that engraves the rifling into the bullet. The pressure spikes very quickly and then decreases quickly as the bullet goes down the barrel.
Quite a different scenario occurs in a smokeless powder MLer. The bullet is only held by the lands with appx 0.0035” of space to the bore. When the powder ignites, the pressure swells the bullet AS IT IS STARTING TO MOVE DOWN THE BARREL , so unlike the cartridge rifle where all this engraving occurs at a finite place, this land engraving/obturation over a much greater distance. How far down the barrel this takes? I have no idea. A smooth sized bullet would go farther than a full sized bullet (452 or 402) and surely farther than a full sized, bore size bullet (458 or 408).
FWIW, with my comparatively low to moderate loads, I full size in order to shorten the obturation distance and hopefully to increase the consistency of the obturation distance. I anneal monolithic bullets for the same reason.
Many early PT calculations verses QL estimates were fairly close, but most were done with saboted loads (which obturate quicker than bore sized bullets) and with comparatively fast powders. I believe that the differences between PT and QL calculations would be much greater with smooth sized bullets and our slower powders. However, the elongated burn causes the calculated speeds to be uncannily close. Actually, with a high percentage burn, virtually the same total energy is obtained- just over a longer distance, which results in about the same energy imparted to the bullet. So, virtually the same speed results.
In summary, I believe that there is a much longer sustained pressure in a smokeless MLer resulting in close to the same velocity as a CF would have with the same bullet wt and powder but with a significantly lower peak pressure(in the MLer).
If you were to take a 8-9# total weight rifle (like my ultralite 40, or a light break open) and shoot it, say with a 250g bullet @ 2,800’/sec and then the same wt CF rifle with the same wt bullet/velocity, the perceived recoil would be radically different. The CF would seem much more brutal as it is a virtually an instantaneous jerk whereas the MLer would feel much gentler. The difference is - the obturation distance which greatly lowers the peak pressure.