“...Mine flew A-36’s. P-51 with more guns, dive brakes and bomb racks.” [FrozenAssets, post 22]
All P-51 variants (including the A-36) mount four guns until the P-51D, which mounted six. Ammunition supply lasted about 12 seconds.
According to photos I have the A-36’s that were operating in North Africa, Sicily, and Italy had the four 50’s in the wings like the 51’s but they also mounted an additional 50 on either side of the cowl just aft of the prop. The A36 was a lot like the B model 51 with the “birdcage” canopy.
The big performance difference was that the A36 had an Allison V1710 with no turbo as did the early 51’s. The 51 really came into its own with the Rolls Royce turbocharged Merlin. Both were quite formidable at lower altitudes but the Merlin equipped versions had much better high altitude performance.