Help with unknown Royal Laboratory cartridge dated 1918


Have been unable to find this inert cartridge in any of my searches, therefore; would be grateful for any help with identification.

Headstamp appears to indicate:
Royal Laboratory 1918

No magnetic attraction.
Three distinct neck crimps.

Measurements are as follows:

Case: 2.446"
Bullet (that can be measured): 0.30
Rim: 0.534
Base: 0.503
Neck: 0.341
Total Length: 3.04



Experimental .303 Rimless, I’ll grab a link to some more information in a sec for you.

Chambered in P14 rifles for the British Army and in Lewis Guns for the RAF.


Here is the link.

Pretty cool round. Nice addition to ones collection.


Hi Guin,
Many thanks for your rapid response…greatly appreciated!

This IAA Forum is truly outstanding.

Thanks again & regards,


Often called a “.303 Lewis Experimental”.


Many thanks.