I just dug out my British 1.5", No4 Mki* Aircraft Flare Pistol, and noticed the short chamber: 1 5/16" in a 4" barrel.
My ONE kilgore No. 52 fits, but wiggles around just a tiny bit, and my modern, reloadable, polymer case round also fits, (closed on this round in the last photo), but…
… I have noticed that some 1.5" flares have a slightly larger diameter base that extends above the rim, sometimes to about 2 inches, which prevents them from chambering in several 1,5" flare guns.
I have a Sedgely, 1 5/16" chamber, & an International, 1 5/16" chamber, that the two flares shown willl not chamber in.
They will, however, chamber in my Signal Pyrotechnic, bored through with no distinct chamber, and my Kilgore, with a 1 5/16" chamber, (which are otherwise the same design), just fine.
Then there is the Federl Laboratory Gas Gun, 1.5 Caliber, which is also bored through, and has accepted every 1.5" flare/smoke/teargas shell that has been put through it.
So, my ultimate question:
Is there something/someone/somewhere that has good, hopefully detailed, information on 1.5" flares and/or chambers, and differences in rounds?