RAF Mustang I rifle cal MG armament--.30s or .303s

[BarnOwlLover]

Looking for confirmation here about the RAF's Mustang Is as far as rifle caliber machine guns. I've seen numerous sources say they were .303s, which logistically would make sense, given that was British ammo. But I've seen references (including maybe Colin Ford's WingLeader Allison Mustang book) that the Mustang Is had .30s on it. Don't have access to that book at the moment, but could someone verify which is that case?

 

[Greyman]

Looking for confirmation here about the RAF's Mustang Is as far as rifle caliber machine guns. I've seen numerous sources say they were .303s, which logistically would make sense, given that was British ammo. But I've seen references (including maybe Colin Ford's WingLeader Allison Mustang book) that the Mustang Is had .30s on it. Don't have access to that book at the moment, but could someone verify which is that case?

.30s

 

[ColFord]

RAF retained the 0.300in US armament as supplied, never swapped them out for UK/RAF spec 0.303in MGs. One of those annoying myths that will not go away and keeps popping up. People keep asking why RAF didn't change over, well they already had other US supplied aircraft (and others on order) fitted with the US 0.300in MGs as a part of their armament fit out eg some versions of the Tomahawk, so there was already a support and logisitics line in place. To swap out the near 2,500 supplied as a part of the initial Mustang I contracts, plus spares, would have required taking aircraft 0.303in MGs from some other RAF type already planned, plus they would have had to modify all the ancillaries already fitted to the Mustangs. RAF didn't see the need to expend that much effort.

UK in 1939-1940 had purchased millions of rounds of 'old stock' 0.300in and 0.50in ammunition from the US Government as well as directly from US manufacturers to use with the MGs and HMGs they were purchasing and having supplied with their various aircraft and other armaments orders. The purchase of the 'old stock' US Government ammunition, was then backfilled with new manufacture ammunition for the US Government. That also bolstered the US armaments manufacturers in ramping up their manufacturing capacity and provided some surety for the scale of orders going forward before the US entered the war in December 1941.

Extract from the Air Ministry issued Pilot's Manual for the Mustang I.

And an example from the combat reports from one of the RAF Mustang I squadrons from 1943, armament report following an offensive operation over the enemy territory, showing armament fitted, ammuntion types, rounds expended, stoppages, etc. Some other units sometimes gave an even more in depth report that broke down ammunition by sub-type eg incendiary, ball, tracer, AP.

The combat and other reports for the other RAF units using the Mustang I up until early 1945 show same armament and similar level of details.

The other general misconception about the wing mounted armament for the Mustang I is the placement of the MGs and HMGs - a number of books say the 0.50in HMG was in the middle position between the two 0.300in MGs, but in fact the 0.50in HMG was in the inboard - closest to the fuselage - position in each armament bay, with the two 0.300in MGs in the outer positions. One of the photos I included in the Wingleader Photo Archive book clearly shows the layout, complete with letter or arrows to point out what is where from memory.