synchronisation

[Tony Williams]

As far as the effect of synchronisation is concerned, I would regard a 10% reduction as the minimum, which probably only applied to the best systems. I have very little actual data, but I would expect the German electrically-primed system to be the best. Most other systems would, I think, be operating at more like a 15-20% reduction.

However, I wouldn't get too hung up about precise RoF figures, because in real life they did vary. Even with unsynchronised guns, the state of wear of the gun, the type of ammo used and even atmospheric conditions could affect the RoF, which was only ever an average figure (this is true even today; the RoF of the current Russian 30mm GSh-301 fighter gun is officially listed as "1,500-1,800 rpm"). Add synchronisation and there is a whole new set of variables.

The following extract (a freebie from my next book ) contains the only detailed assessment of synchronisation which I have been able to find:

"An example of the effect of synchronisation is graphically provided by comparative tests held by the USN in 1926/7 of the .30" M1921 and .50" M1921, both on a test stand and in synchronised mountings. These also shed some light on the differences between claimed and actual rates of fire, and between different installations of the same gun. The .30" had a claimed RoF of 1,200 rpm, but proved capable of between 800 and 900 rpm on the test stand. When synchronised, the RoF went down to an average of 730 rpm (a fall of about 15%), with a range of between 667 and 818 rpm for different installations and propeller speeds. The .50" had a claimed RoF of 600 rpm, and did rather well to achieve between 500 and 700 rpm, depending on the recoil buffer adjustment (although a contemporary British report put this at 400-650 rpm, the difference possibly caused by belt drag when installed), but this fell to an average of 438 rpm when synchronised, varying between 383 and 487 rpm. As the synchronised guns were adjusted for maximum RoF, this represented a reduction of around 37%."

Tony Williams
Author: "Rapid Fire: The development of automatic cannon, heavy machine guns and their ammunition for armies, navies and air forces"
Details on my military gun and ammunition website:
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[Tony Williams]

I have been communicating with Doug Balmos on this subject, but for some reason my replies to his email keep getting bounced back. Can anyone help?

Tony Williams
Author: "Rapid Fire: The development of automatic cannon, heavy machine guns and their ammunition for armies, navies and air forces"
Details on my military gun and ammunition website:
http://website.lineone.net/~a_g_williams/index.htm
Military gun and ammunition discussion forum:
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[HoHun]

Hi Tony,

under the assumption that the synchronization system triggers once per 360 degrees, the figures you quote indicate a propeller speed of 1930 rpm for the 0.30" test.

For the 0.50", it's more complicated.

With the propeller speed at 1930 rpm, there would a trigger impulse each 31 ms, and gun cycle time would be 86 ms at 700 rpm. This would normally result in an average rate of fire of 591 rpm. The real rate of fire was far below that - what went wrong?

I'd suggest that the synchronization just didn't work properly, and the gun skipped trigger impulses without firing. Skipping one impulse each time would result in an average rate of fire of 453 rpm - actual average was 438 rpm, so this explanation matches the data very well.

In short, I don't think that this test installation was representative for the fully developed systems that were featured by WW2 fighters.

Regards,

Henning (HoHun)

[Tony Williams]

Originally posted by HoHun
In short, I don't think that this test installation was representative for the fully developed systems that were featured by WW2 fighters.

I think that is correct in general, although there were considerable variations. The British tested a P-40 in around 1940, IIRC, and reportedly concluded that they disliked the synchronised .5" fitted as the rate of fire was only around 400 rpm.

The Japanese Army also complained that their Ki-43 fighters fitted with synchronised 12.7mm Ho-103 had a very low rate of fire, which seems to have been little more than half the unsynchronised rate.

Tony Williams
Author: "Rapid Fire: The development of automatic cannon, heavy machine guns and their ammunition for armies, navies and air forces"
Details on my military gun and ammunition website:
http://website.lineone.net/~a_g_williams/index.htm
Military gun and ammunition discussion forum:
http://www.delphi.com/autogun/messages