Unknown British (?) 20mm Projectile

[roadrunner404]

Morning All, I was wondering if anyone can shine a light as to identifying this 20mm projectile for me at all. I'm assuming that it is British made as there are 3 War Dept arrows in a line on the base plate. There are 8 LH rifling grooves on the very worn 5mm wide driving band at a near 45 degree angle (which seems a bit steep) & a 1.5mm wide crimping groove, 1.5mm below it. overall length is 83mm with two changes to the ogive profile, 1 at approx. 5.5mm from the tip & the other at approx. 25mm. There are no stamps or markings anywhere else on the shell body. There is no fuze fitted so I'm assuming it's an AP round but Labbett & Mead's Tech Ammo Guide for British 20mm Hispano rounds doesn't seem to make any reference to a shell of this profile. Apologies for the quality of the photos but they're the best I can do. Any help much appreciated. Regards, Ian.

 

[TimG]

In the early 1940s ROF Steeton used three pheons (Broad Arrows) as a headstamp, prior to being assigned the code "ST" Amongst other stores they manufactured 20mm.

TimG

 

[roadrunner404]

Thanks for that Tim. I haven't got one of those cases in my headstamp collection of Hispano cases yet, will keep an eye out for one. I do have the early RG case that has one arrow on it though.
Ian.

 

[kahu1]

Possibly an early AP capped (minus the bakelite cap). Does it have any (faint) sign of notches near the top 1/3rd?.

The shell shows signs of heavy wear, so likely the DB has only the extreme impression left on it, usually there is impression and some extrusion (spreading) on the DB. 45 degrees would be an unrealistic angle for effective rifling on a high velocity round.