WWII RAF Gun Harmonisation

[Greyman]

As mentioned last year: http://www.ww2aircraft.net/forum/aviation/why-did-raf-persist-303-throughout-war-37878.html ...

While my article isn't entirely finished and not quite ready for 'prime time', I figured I post my mostly complete write-up as a preview:

Gun Harmonisation

Love to hear any questions, comments or suggestions.

 

[pinsog]

Nice beginning. What is the size are the target rings in your example?

 

[Greyman]

Nice beginning. What is the size are the target rings in your example?

On the 'Bullet Group' page there is no size, it's just a representation of a typical group. The size varies depending on what aircraft and in which mounting the gun is located.

On the 'Harmonisation Pattern' page the first three groups of images are typical groups from an eight-gun Spitfire (I or II). They're not from specific tests but are for illustrative purposes. These are a little larger than 1/3 of a degree (75% zones).

In the fourth group of images (typical groups from a Spitfire Vc), the darker groups are from the cannons, and are slightly smaller than 1/3 of a degree (75% zones).

 

[bobbysocks]

how was the 303 browning mounted and was it shot in short bursts or did they run the belt? even at 50 yards if mounted on a tripod and shot in bursts by a trained gunner ....the group should have been tighter.

 

[Greyman]

I don't have specific figures for the Spitfire as of yet, but 1/3 of a degree is typical of a wing-mounted gun, and I'm sure is close to the average group from a Spitfire.

 

[Shortround6]

There are a number of things that can affect the grouping of a Browning machine gun. The guns can certainly be set up to shoot better if that is what is wanted. The "cooling" jacket is also the support for the forward barrel bushing and the tightness of this bushing affects things as does the headspace adjustment and buffer.
With the emphasis being place on shotgun like (or worse) patterns perhaps the 1/3 minute zone was a deliberate set up of the gun itself.

I would note that the RAF was not alone in this pattern thinking as the quad .5 Vickers naval mounting had each gun pointed in a slightly different direction which certainly increased the chances of getting a hit even if if it didn't do much for actually shooting down a plane that needed multiple hits.