It could be there were looking at skinny barrel walls in military-type rifles in the larger bores- or seemingly light maximum loads listed by manufacturers.
For pressure reasons, I stick with 2F for larger bores - from .50 up - 2f has ALWAYS given me better accuracy in those rifles over 3F. It does take more 2F to achieve that accuracy and match 3f speeds, but- 2F does not foul more than 3F WHEN you use a decent ball and patch combo- ie: snug.
If you refer to the old Lyman BP handbook, you can see a relationship between velocity and pressure - all the way up through the calibres using either 3F or 2F.
Using a .54 bl. and 2F, at a certain speed, the pressure listed is very similar to the same velocity produced by 2F in the .58 they used, however the .58 needed much more powder to achieve that velocity and thus that pressure. This is ALL logical and is as it should be.
Thus, at 1,700fps in a .54, the pressure produced is the same as the pressure produced in a .58 at the same speed. it takes a LOT more powder to do that in a .58 - hence, to get a flatter trajectory in a larger bore, you need to feed the rifle more powder and soak up the increased recoil - same as with modern rifles- very little difference. The larger the bore, the more powder it takes to produce the same speed - but - the pressure is the same or less than what the smaller bore produced at that speed- generally.
As to lighter chargers in the .58's- many Italian companies list max pressures at 8,500cup/lup/psi or around there- thus published data will reflect that. For example, their data for the .72 side by side Kodiak is something like 85gr.2F. That charge in that bore size will produce something like 1,100fps-maybe. Some of the guys on another forum with those rifles are getting regulation at 150 to 175gr. T7 of all things. I do NOT recommend those loads or those that follow. Others are using 150 to 175gr. of 2F GOEX and getting reasonable regulation of the barrels.
Others find it does not matter what they do they won't regulate.
