From my sources of information, namely "The Complete Book of Fighters" (Green and Swanborough 1995), the P47 or Thunderbolt, was begun production with 8 x .50s, then in December 1942 the P47G appeared as a minor modified version of the B and C series, but built by Curtiss Wright, rather than Republic (there was no A series). These were available with either 6 or 8 x .50s and additional ammo as standard, no reason is given for the differences. These were built at either Farmingdale or Evansville.
Really makes me wonder why a large fighter like the P47 was armed with .50s in the long run. It would easily be capable of carrying larger (and more capable) weapons such as the HS 20mm, or whatever was going at the time. This would have made it far more capable I believe.
Carrying such a huge lump of engine (2300 hp), it was always destined to be a big aircraft. Everthing has a price though in AC design, the first three important factors being; mass, mass and mass. All concepts for AC are based on airborne mass, so a heavier fighter needs consequent larger landing gear, larger fuel load, larger controls, larger wing spars, this all leads to a multiple effect..thereby making the whole AC heavier by a multiple rather than an addition.
Another important consideration for the P47 is its surface area. Being larger than others (such as the 190), it has a far larger area, which naturally leads the AC to be heavier...there is no way around this, except for the AC to be "skinny" in the fuselage like the 190 which is very narrow, and consequently lighter because of this. This is one reason why aerodynamisits like V type engines..they were quite simply smaller in frontal area, leading to an easier transition for a skinny fuselage.
In surmising this, fat is heavy, skinny is light. A lighter plane needs smaller wings / controls / UC / skin thickness / engine mountings / ad infinitum, for the same performance in any aspect, and can do the same with less horsepower.
It is clear the high altitude performance of the P47 is due to the concerted effort of the engine designer to obtain a positive intake ratio at higher altitudes (by multiple supercharging). We now are verging on the whole reasoning behind gas tubine (jet) engines and their superior high altitude performance.
