Gladiator fuselage guns

[Dinger]

Hi, I wonder if anyone out there can help with the answer to question that has been bugging me for some time now. I've looked up every on-line resource I can find but come up a blank. It concerns the use of Browning machine guns in the fuselage positions on RAF Gloster Gladiator biplane fighters. My understanding is that when the RAF adopted the US Browning M1919 for aircraft use they not only changed the calibre to .303 but also made it fire from an open bolt to avoid "cook-offs" and also potentially allow longer bursts of fire. But one of the disadvantages of an open-bolt is that it makes a weapon unsuitable for use with a gun synchronisation or interrupter gear to fire through a propeller (the variable delay in closing the bolt being the factor in making it unusable ). Now the Gloster Gladiator used the well tried Constantinesco synchronisation gear that had been the RAF standard since the end of WWI, and that certainly needed a closed bolt weapon in order to work. When the Gladiator was first introduced it used two of the older Vickers Mk V machine guns in the fuselage which operated from a closed bolt, so they would have not been a problem (I'll add at this point I already know that the wing mounted guns were in turn Lewis, then Vickers K then Browning just to stop someone posting that bit of commonly known info). - My problem is that every detail history I can find of the Gladiator says "it ended up with all four guns being Browning". - How can this be? - Were the fuselage Brownings modified to fire from a closed bolt somehow? - Or where American .30 guns and ammo used instead (highly unlikely in my view) or was the synchronisation gear modified in some way to overcome the problem? - Or have the reference books just got it wrong and Gladiators continued to use the Vickers gun in the fuselage positions? (I would assume that with all the Vickers guns stripped from Gauntlets and Demons and similar aircraft that came out of service at the time that there would have been no shortage of these weapons anyway). I cannot find any other RAF aircraft that used .303 brownings firing through the propeller (the Tomahawk, Mustang I and P-400 Airacobra used the bigger .50 calibre Brownings which fired from a closed bolt, the Australian Wirraway used old Vickers Mk V guns firing through the propeller while the Canadian Goblin 1 used American .30 Brownings). Any musings welcome but hard evidence or reference to written or online sources that could shed light on the question would be appreciated. - Thanks in anticipation.

 

[Greyman]

From Anthony Williams:

The 7.92 mm German MG 17 retained percussion priming and was able to utilise open-bolt firing (with the benefit of reducing the risk of ammunition cook-off in a hot chamber) by having two sears. The sear holding the bolt open was released by the pilot pressing the firing button, but once the bolt was closed there was a second sear holding back the firing pin, and that was released by the synchronisation system, via an electrical solenoid. The RAF's .303 inch Browning utilised a similar system in the small number of aircraft using synchronised installations early in WW2 (most notably the Gloster Gladiator). Incidentally, the USAAF Brownings fired from a closed bolt; their gun propellant was less inclined to cook-off than the British Cordite.​

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From the Air Historical Branch:

In July 1941, the question of testing guns for use in aircraft fitted with synchronising gear was raised by the Armament Research and Development branch. Originally all guns had been tested at the manufacturers and this caused considerable delays in passing out guns. Only a proportion were now tested and the remainder stamped 'NTS' (not tested for synchronisation). BSA had experienced no failing of guns to pass this test, and as the number of aircraft fitted with synchronising gear was rapidly diminishing it was decided to abolish it altogether, for, owing to the small number of aircraft concerned, the chance of an unsuitable gun being fitted to aircraft with interrupter gear was small.​

 

[Dinger]

Fantastic 5 star reply - perfect concise answer. Thanks!

Dinger