Bofors gun fuze destruct delay

[BMG50]

As we know the 40mm AA Bofors gun projectile has two fuzes. One a impact at the front obviously. The other fuze at the base for self destruct. So if the projectile misses the target it explodes at a set time when the base fuze is timed out, so the projectile doesnt travel to the next town or village and disintegrates into a thousand pieces in the local vicinity avioding projectiles becoming live EOD when they land if they fail to go off. I was wondering if these base fuzes had different delay times, so if your target was at 3,000 feet your the base fuze would explode the projectile at this point but if your targets were say 6,000 feet or closer at 2,000 etc they would explode too soon or too late. Were there different delays or just one standard fuze that set off at a certain distance and acted as more of a deterrent to aircraft in the guns lethal range.

 

[Eggburt1969]

Firstly, what county's and what service's 40 mm Bofors high explosive (HE) projectiles (shells) are we taking about? The UK, America, etc...

For the UK, it has a fuze at the front, but the rear item is a tracer and igniter assembly (Tracer and Igniter Shell No. xx), it's not a fuze per sec.

Those listed in the UK's 1949 Anti-Aircraft Ammunition publication, and stated to being used with the 40 mm Q.F. HE shell, are as follows: Tracer and Igniter Shell No. 11; Tracer and Igniter Shell No. 12; and Tracer and Igniter Shell No. 14. Of these most had at either two, or up to three, Marks (Mk.) by 1949.

Going by the UK's aforementioned publication, the various tracer and igniter assemblies had a nominal 6.5 second functional delay. This delay will however vary due to pyrotechnic compositional variation and composition's pressing (force) within the assembly. The time delay will also vary due to atmospheric effects.

 

[BMG50]

I was talking about wartime UK. The base fuse also acted as tracer and burnt out to igniter to exploded the shell. I assume there were tolerances that affected the action of projectile but what was the spec of delay of the three, as you mention they were all at 6.5 sec delay, what distance on average did the projectile explode at give or take conditions. Looking at the delay of 6.5 seconds upon firing ignition of the tracer in the barrel and 6.5 sec distance of igniter in fuze exploding projectile looks like 5,000 to 6,000 feet, not sure.
I thought you could use same type ammo but with different bursting delays, if the aircraft being shot at was close or very far away.

 

[Darkman]

Early Mk 11 & 12 tracer-igniters burnt for 6.5 seconds, but Mk 14 was 12 seconds

 

[BMG50]

Interesting, so would a Bofors crew have two types of ammo ready for short or long range gunnery when the target presented itself or even mix, was this judged by the loader etc. Not sure how it worked. Of course the Proximity fuze was a game changer later on but, so i am told was to big to fit a 40mm Bofors projectile or even a L70. Correct me if i am wrong, trying to find out facts for a talk about gunnery using the Bofors gun, not sure if there was a weapons training pamphlet denoting practice and proceedure.

 

[Eggburt1969]

Early Mk 11 & 12 tracer-igniters burnt for 6.5 seconds, but Mk 14 was 12 seconds

Indeed, all Marks of the Tracer and Igniter Shell No. 11 and Tracer and Igniter Shell No. 12 in the 1949 UK book are listed as nominally 6.5 s.

The book only lists Marks 1 to 3 for the No. 11, and only Mk. 1 and Mk. 2 for the No. 12, so that's all I've got data on.

For some reason I misread the No. 14 details and for Marks 1 to 3 listed, which are listed in the book, the nominal time delay is 12 s.

Interesting, so would a Bofors crew have two types of ammo ready for short or long range gunnery when the target presented itself or even mix, was this judged by the loader etc. Not sure how it worked. Of course the Proximity fuze was a game changer later on but, so i am told was to big to fit a 40mm Bofors projectile or even a L70. Correct me if i am wrong, trying to find out facts for a talk about gunnery using the Bofors gun, not sure if there was a weapons training pamphlet denoting practice and proceedure.

No idea about having a mix of SD times, and hence ammo with No. 11/No. 12, and some No. 14 for longer ranges. The proximity fuzes during WW2 were pretty large, probably due to the old analogue electronics within them, and these components requiring quite large reserve batteries, this all took up space.

 

[tankbarrell]

As I understand it, the tracer igniter was simply intended to show trace and destroy the shell whilst still in the air to prevent damage to friendlies. It was not meant to detonate the shell in the hope of destroying the target.
The nose fuze was an impact fuze and that is how the target was supposed to be engaged.

 

[BMG50]

As I understand it, the tracer igniter was simply intended to show trace and destroy the shell whilst still in the air to prevent damage to friendlies. It was not meant to detonate the shell in the hope of destroying the target.
The nose fuze was an impact fuze and that is how the target was supposed to be engaged.

The thing about the nose fuze is, you have to be very very lucky to hit an aircraft target, an exploding shell in the vicinity of the aircraft would give you more luck of a strike plus the exploding rounds would be more of a deterrent to the enemy, you wouldn't want to encounter a flak burst. The trace and destroy was the main goal, flak being a bonus. Interesting to find out what the design concept was.