Not sure I agree with that. It has more to do with baring surface and sectional density more then anything and that can be proven time and again.
For instance, you take two rifles, just to keep things consistant the same 300 WSM and 338 WSM and take a bullet in each caliber that has the same sectional density as the other caliber bullet. In this case lets look at the 165 gr 30 cal with a sectional density of 0.248 and the 200 gr 338 bullet with a sectional density of 0.250.
In the same length barrels and same chamber pressures, the muzzle velocity of each bullet will be nearly identical. Variations in specific bullet and lot of powder will make more difference then anything else as to the velocity difference in these two bullets.
Why is that? in my opinion it has to do with similiar Section densities more then anything else and may be I should have stated that instead of baring surface.
Another example, look at a 7mm Rem Mag compared to a 338 Win Mag. Compare a 175 gr bullet in the 7mm with a SD of 0.310 with a 250 gr 338 bullet with a SD of 0.313.
In most cases the 7mm Rem Mag will get you around 2825 to 2875 fps in a 24" barrel. The 338 Win Mag will get you 2750 to 2800 fps with the 250 gr pill so again, basically identical with same SD bullets.
However if you go with the same weight bullets in each caliber, or similar, the 338 will smoke the 7mm REM Mag in velocity potential. Not saying ballistically it will be superior but as far as velocity potential it will be far superior.
The 7mm will also be much more dependant on barrel length as well.
Another example would be comparing a 22-250 to a 6mm-250 both using 55 gr class bullets. The 22-250 will top out around 3700 to 3800 fps depending on barrel length. The 6mm-250 will push 4000 fps with this bullet weight many times and generally well over 3900 fps.
If you compare same SD bullets in each caliber or at least similiar SD bullets such as the 55 grain bullet in 22 cal and the 70 gr pill in 6mm, the velocity potential will be very similiar.
I think your arguement has more in similiar with my comments then we think to be honest. Your saying the larger bore allows more PSI to be applied to the bullet base. Perhaps to some degree, but it also allows or requires the use of faster burn rate powder because of the higher expansion ratio to maintain that PSI on the bottom of the bullet. As such, that type of powder requires less inches of barrel to reach a certain velocity level simply because bullet accelation is more aggressive with a faster burning powder. This is the reason the larger bore diameters are less dependant on long barrels to reach full velocity potential.
Again, I probably should have talked about SD instead of baring surface because in fact, even though the Baring Surface on the 338 is shorter then the 30 cal bullet, because of its larger circumference it is probably at least as large measured in square inches then the 30 cal.
Sectional density is a much more accurate comparision number.
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