I found two sources that appear to have conflicting information about the number of rounds the guns carried. Here are the relevant sections from each source:
Pilot Training Manual for the Mustang wrote:
The maximum ammunition capacity is 400 rounds for each of the inboard guns, and 270 rounds for the center and outboard guns.
...
An alternate installation is possible... The center guns are removed; this allows 500 rounds of ammunition to be carried for each of the outboard guns.
F-51D Mustang Handbook wrote:
Either of two gun installations is possible: (1) three fixed .50 caliber guns may be installed in each wing, with 500 rounds (400 in late airplanes) of ammunition for each inboard gun and 270 rounds for each center and outboard gun; (2) the center gun may be removed, allowing the inboard guns to carry 500 rounds (400 in late airplanes) each and the outboard guns to carry 500 rounds each.
So, the question is: How many rounds did the guns carry on the P-51D and when did it change?
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