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20 X 178 Rarden.


Well-Known Member
Premium Member
Another of those high speed test rounds, shown on the right in the first photo - the 20mm Rarden.
I've attached a few close up pictures of it.
Stamping on the case is number 8 plus some engraving on the side of the case. Projectile is also number 8.
Note the heavy duty crimping on the case.
All INERT etc.


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Thanks for sharing. Very interesting! I haven't seen the Rarden before and I haven't seen one of the L/60 40mm bofors necked to 20mm for some time.

Hi John, thanks, what sort of projectile did the Bofors 40/20 have in it that you saw?

I've seen/heard of 2 like mine and an HE so far.........and the line drawing in the De Hek books shows a cored projectile.

Primer size/type ?

Hi David do you know what thread the case has for the primer and is it for an HS831L standard primer ?

See attached photo (sorry it is not a good one)


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Primer measurements.

Hi Chris, yes I'd like to know what sort of primer it takes as well.

The primer hole on the standard case I've must measured is 15.3mm in diameter with the threads 10.70mm.

The primer hole on the 20mm case is 12.77mm for the primer hole and 9.50mm for the threads.

Anyone any ideas? Perhaps Charlie can help out on this one being the Rarden expert??


I can't tell you what projo the 40/20 had. It was 20+ years ago when I saw it. In speaking with other collectors at the time, one told me that it was a test for 20mm high velocity, and that it ripped the rotating bands off the projectiles when they were fired. Looks like a 22 Rem jet round on steroids! Probably 90% urban legend!