The UK's Finest Independent Forum for Shooters and Gun Owners. Est 2010.

I have come a cross a .303 case that was made into a knife holder, the handle of the knife looks like a bullet and the blade goes inside the case, friction held in place.

The headstamp is R "Broad Arrow" L and then 1 on the other side from Broad Arrow.

My creaking memory suggests that RL is for the Royal Laboratories Woolwich and the 1 suggests it is a MK1 cartridge so 19th century.

Anyone know any better on this?

My creaking memory suggests that RL is for the Royal Laboratories Woolwich and the 1 suggests it is a MK1 cartridge so 19th century.

Sounds about right to me.

Royal Laboratories is correct and I have (had?) a .303 case with that headstamp dated 1937

According to
https://cartridgecollectors.org/headstamp-codes/#
you are correct on the Royal Laboratory front.