.55 in Boys Anti Tank Rifle Ammunition

I inherited and box of old military gear, inside I found this. I have no clue about the history of it though.

I believe it is a .55 Boys anti tank rifle drill round, correct me if I’m wrong .

Can anyone tell me what type of rounds these are and what the markings mean?



Good afternoon Northover,

I believe what you have is a Cartridge S.A. Drill .55 inch D Mark I, you can get more info from https://sites.google.com/site/britmilammo/-55-inch-boys-2/-55-inch-boys-drill-dummy, an excellent site

Regards John P

1 Like

Hard to tell without a side view. The .5" Vickers drill round exists with the same head stamp.

1 Like


.55 Boys

“O” Mk.I is Inspection, Not Drill, which is “D”.
Inspection rounds were better made, for use by Armourers, for Mechanical Inspection of Arms.
DRILL ROUNDS were for regular training use, and suffered more damage.
Doc AV.

U is inspection, O is observation/explosive…the headstamp above clearly shows D for drill round.

Here’s a .55 Boys Inspection dummy.


Does anyone have one with the “O” on the Bottom … really interesting topic.

Also, what does the K stand for on the Inspection round?


O does not exist on .55 boys ammunition to my knowledge. Only on .303.
The K stands for Kynoch who made the case.

That shall be “Kynoch”, the manufacturer.

“O” ? Is is filled with red paint?

The “O” being for observation. But it was answered that the .55 didn’t have an “O” model.

I was aware of that but wondered if you meant the Dutch marking for inerted ammunition.

Hi Guys,
I only mentioned O for observation in response to DocAV4901s post
’ “O” Mk.I is Inspection, Not Drill, which is “D” ’ which is incorrect