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I recently read here http://www.ammunitionpages.com/download/130/japanese about a series of fuzes, employed by the Japanese, for their 20mm autocannon rounds, which didn't use the usual striker but relied solely on a column of hot air to fire up the lead azide capsule.
Does anybody have more info or actual pictures of these fuzes?
It seems to me quite a dangerous and not very efficient fuze. Dangerous because there is no safety mechanism. The starting capsule is practically exposed on the nose of the shell at the end of a very short passage. Not very efficient because the 'air piston' striking the capsule solely depends on the shell hitting head on something that is hard enough to flatten the head of the fuze squishing the air in it. Its only advantage to me seems that is cheaper to produce as it doesn't need a lot of precision machined parts. Was it a 'last ditch' design employed in the last months of war?
Interestingly (and probably unsurprising) it was the French that figured out the Hispano fuze functioned with the entire striker mechanism omitted. The British 253 strikerless fuze was developed based on these 1939 trials.
The main reason for the switch was the over-sensitivity of the original French/No.252 fuze.
The RAF were aware of this problem, which made the original HE shell with a strikered fuze relatively ineffective. Ultimately, this was solved with the air-column fuze in the HEI shell (the incendiary element added to its destructiveness) but in the short term, the solution was to fire "ball" (target practice) rounds which had inert projectiles. The destructive effect of 129-gram 20mm high-velocity projectiles was quite impressive even without any explosive filling.The sensitivity of the French fuse was intentional: they were worried about cannon shells passing straight through fabric-skinned bombers without effect. Unfortunately, they ended up a bit behind the times when the Germans showed up with all-metal aircraft and all of the cannon shells scored surface detonations ...
Greyman, would you share a reference? I am always looking for more technical information on weapons and engines. Thanks!
The sensitivity of the French fuse was intentional: they were worried about cannon shells passing straight through fabric-skinned bombers without effect.
Bofors 40mm L/60 with what appears to be an air compression fuze:
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