Unknown Cartridge to me 38x122R like british 1 1/2" Anti-Rio

I got a box of this, but the box gives no explanation what it actual is.
It has the same dimensions as the above mentioned 38x122R Anti-Riot case, with a stepped case (Rim about 42,8 (+/- 0,15)
Base 39,5mm, and after the step 38,55 (to 38,60)mm.
But instead the normal percussion primer this unknown ammo has an electric primer, from which the center rod protrudes about 0,4mm out, means the cartridge cannot stay flat on its base.
The only markings it has, is a yellow cardboard closing disc, sealed in the same color and a sidestencelling of the following:
HP 4255
Cartr. Type B
for HP 4250 MPD

(Weight 176 Grams)

and I have an eqivalent other one with a black closing disc and the following writing:
Cartr. Type A
for HP 4250 MPD

(much heavier weight at 274 Grams)

Can someone enlighten me, what it may is made for??

Sorry no pics

Here Peter’s images:

Maybe with the pics someone knews, what i got there…until now I couldnt find out…thx for your help

How about an engine stater cartridge?