Winchester I MK 1 ignition cartridge

Hello all ! Normally after searching this forum I find what I need after a very short time and I definitely want to have all my “i’s” dotted and “t’s” crossed before I attempt to ask a question as I have been reading and enjoying all the history and knowledge that y’all have. I got this green paper shotshell ,non magnetic, copper primer, brass head, stamped Winchester at 10:00-2:00 and a capital I at 6:00. Inside headstamp and concentric circle is a tint of green as I seen with loop . Top was has hole, not me. Four indents from crimp?
Measurements: shell-.800
Sorry about pictures as I don’t have a decent camera yet. What does the letter I mean ? Any significance to it as a whole? Thank you and I will enjoy any tips on posting.


It is a Mark I ignition cartridge for the 3 inch mortar. The indents are for tighter fit inside the mortar shell and the hole in the wad is for identification.



A flare? Sorry, Fede posted the correct answer seconds before me.

Awesome thank you ! I have been so hesitant about posting as in a way y’all have been my teachers for so long and I didn’t want to start off on a bad leg. So would they come in different colors or other identifying marks signifying different strengths for distance or is that up to launcher, gas release sleeve ,holes something similar?


Philip, the range was determined by separate incremental charges which were attached to the fin section depending on the intended firing distance.
There is few exceptions but that shall not matter here.

Here small overview from a Serbian manufacturer (the first I found for a quick reference).

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OK thanks EOD, I do appreciate it!

I think these might be a little later variation, with the REM-UMC being hard to find.

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BTW, are these 12GA now?

Can you show what the bodies look like on these?

here ya go Dave & Alex the head is 20.33mm / .800 inches. Head on a random 12 bore was .805".

Pete, thanks. So it should ba a 12GA case right?

Just slightly smaller Alex but very close.
The Winchester is unfired & has the bulge, the Rem is fired & has the bulge but no bulge on the unfired & loaded Federal. & no explanation for that

I’ll have to keep an eye out for these. I haven’t seen them out in the wild before!

Pete, what GA cal would it be then?

I am asking because the whole world used 12GA in this caliber range (unless other systems were used).
It confuses me a bit.

This cartridge is explained in HWS Vol 1 page 257. “12 Gauge Mortar Ignition Cartridge”

Sorry Alex 12 ga. as Joe notes

Construction details from the ordnance drawing, 1917:

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There it is . Thanks Fede!