Spitfire Mark V armament question

Ya have to also rememeber that not every round has an identical load. When I’ve been out messing about with the M2’s we’ve sometimes had a round with such a light load it wouldn’t load the next round so ya have to recock the gun. Israeli ammo is a LOT better than some of the Dominican crap I’ve fired.

Read the account of Prince Galzeltine and the JU86P at v. high altitude.

Oh, I know the story. Highest interception in history, wasn’t it?

What I mean is – if the gun on the port wing fires five hundredths of a second earlier than the one on the starboard wing – the maximum difference in firing times for unsynchronised guns firing at a nominal 600RPM – it’s not going to make any noticeable difference to the handling of the aeroplane.

were’t they all recocked with exhuast (ie the guns not the aeroplane’s) and so dependent on the mechanics of each gun?

Sort of. The HS 404 was technically a ‘gas-unlocked blowback’. As each shot was fired, some of the expanding gas pushing the shell up the barrel was tapped off to unlock the steel flaps which held the bolt firmly against the back of the chamber. The remaining gas pressure in the barrel then blew out the fired case backwards, and compressed a recoil spring behind the bolt (the action was cocked at the same time). The recoil spring then pushed the bolt forwards, sliding a fresh round from the magazine into the chamber.

The recoil was such that the gun was allowed to move back about 25mm in its mounting to ease the ‘kick’. This movement was later used to drive the belt-feed mechanism; it tensioned a spring which in turned pulled the belt. To make sure that there was enough recoil to do this job, the slotted ‘recoil reducer’ (muzzle brake) which was fitted to the muzzle of the wing-mounted magazine-fed guns was removed.

Tony Williams: Military gun and ammunition website and discussion forum

A side point is that there were problems with jamming in the early fitting of Cannon to Spitfires. IIRC, this was sometimes caused by wing flex in the turn? Can anyone confirm or correct?

There were two main reasons for the problems. One was that the HS 404 was designed to be bolted firmly to an engine block, to fire through the propeller hub. It did not take kindly to being mounted in a far more flexible wing. The specific problem with the Spit 1b was that the guns were mounted on their sides, rather than upright as designed, in order to bury as much as possible of the big 60-round drum within the wing. And they really didn’t like that at all. The net effect was that the installation was a disaster.

There continued to be installation problems which needed to be resolved in each case when the Hispanos were wing-mounted – even with the big Blackburn Firebrand. Basically, the gun mountings had to be ‘tuned’ for each installation. Mounting the guns in the far more rigid fuselage was much simpler.

Tony Williams: Military gun and ammunition website and discussion forum

Gents
Many thanks. A friend is building a R/C model, and wanted replicate the armaments and firing as authentically as possible. Your information has been very useful.

Is he building an R/C model with live guns?

Read the account of Prince Galzeltine and the JU86P at v. high altitude.

G-A-L-I-T-Z-I-N-E

were’t they all recocked with exhuast (ie the guns not the aeroplane’s) and so dependent on the mechanics of each gun?

Melvyn… yes, that’s true that if you have a gun jam, but when you consider that a Hispano cannon fires 10 times every second, it’s not going to make any difference to the handling of the plane whether they are synchronised or not.
As Rocketeer says, there would be minor differences in the RoF due to cocking times, etc.

Read the account of Prince Galzeltine and the JU86P at v. high altitude.

Thanks Mark.

Oops!

Pneumatic triggering would (potentially) be slightly variable from gun to gun (thinking of the way pneumatics works in other functions) so where does that leave us?

It’s in the air.

???

Its a technical answer, isn’t it? Any gun in a wing with a matching gun in the other wing, being electrically triggered, and ‘at rest’ in the same part of the firing cycle will fire ‘syncronised’ – because the trigger gets the signal the same moment at each gun, which then does the same thing, at the same time. Why would, or how could, there be a difference?

Pneumatically triggered in th case of all Spitfires/Seafires except for some Mk 24’s and the Seafire Mk 47.

Mark

…did everything fire simultaneously? Was there a particular firing sequence or multiple triggers?

The multiple trigger question was answered earlier. My point was that when you pressed the appropriate button, the selected guns would start firing similtaniously; Setter’s points being good about the rate of fire thereafter, and chance /pointlessness of further fiddling with synchronisation.

A side point is that there were problems with jamming in the early fitting of Cannon to Spitfires. IIRC, this was sometimes caused by wing flex in the turn? Can anyone confirm or correct?

Gents
Many thanks. A friend is building a R/C model, and wanted replicate the armaments and firing as authentically as possible. Your information has been very useful.

Hi James

Well sort of, they generally will not operate faster than the cyclic rate of fire but most will be fairly close to the norm all things being equal although if a spring is weak or a gas alley partly blocked or no/poor lubrication / dirty they will be slower or malfunction. If you had time you could “blueprint” all the guns in an aircraft to make sure all the parts were correct in the tolerances /spring rates etc which would in theory give you very similar rates of fire but in practice nobody ever bothered – just keeping them clean and fixing wear when it was noticed was the best that could be done in service and even then barrel wear was fairly rampant in remote locations like the Pacific theatre.

Regards
John p

So they would sorta ‘fire at will’ 🙂

The original question answered methinks.

Hi James

Differences in the cocking mechanisms, recoil springs and gas return flows as well as different levels of friction in each gun will vary and thus one Gun is faster or slower than another and thats why cleaning is so important as well as proper lubrication and attention to wear and tear etc. Never saw two guns with exactly the same cyclic rate of fire despite it being quoted all the time it just didn’t happen.

John

???

Its a technical answer, isn’t it? Any gun in a wing with a matching gun in the other wing, being electrically triggered, and ‘at rest’ in the same part of the firing cycle will fire ‘syncronised’ – because the trigger gets the signal the same moment at each gun, which then does the same thing, at the same time. Why would, or how could, there be a difference?

Melvyn… yes, that’s true that if you have a gun jam, but when you consider that a Hispano cannon fires 10 times every second, it’s not going to make any difference to the handling of the plane whether they are synchronised or not.
As Rocketeer says, there would be minor differences in the RoF due to cocking times, etc.

You wouldn’t have a starboard/port sequence as that would throw the aeroplane off line. There are plenty of accounts of pilots missing shots as one side had a jam and slewed the aeroplane off line.

The two cannon would fire together or the four cannon, or the two cannon and two half inch or the two cannon and four .303 or the .5 on thier own or the .303s. It depends on what was fitted but let’s assume ‘B’ wing on a Mark V.

Press one side and the cannons fire. Both of them. Press the other side and all four machine guns fire. Press the middle and you make REALLY big bangs.

As far as I know, the guns weren’t synchronised at all as that would slow down the rate of fire. So I guess they wouldn’t fire in any particular sequence.

you are correct, only differences caused by airflow delays and pipe lengths and recocking!

As far as I know, the guns weren’t synchronised at all as that would slow down the rate of fire. So I guess they wouldn’t fire in any particular sequence.

Rocketeer
Many thanks, that’s useful, but do you know whether all guns/cannons fired simultaneously or whether there was a starboard/port or inner/outer sequence?