This is a Swedish one made in 1940.
“L” is the factory in Lindesberg, unfortunately there are several ammo related businesses and I do not have the exact name.
I got somewhat further.
This is the “Eldmarkeringspatron m/34” an artillery fire simulator (air burst) - identified by the knurled rim. It existed in two versions, one with a white smoke puff, and one with a black smoke puff.
The case heads were painted in the regarding color.
In Sweden the caliber is designated as “25mm” and would be today the better known 26.5mm.