Is the compound CM-7 in Red Comet fire grenades azeotropic dichloromethane?
Passive fire suppression systems by Red Comet included a glass bulb with colorless transparent liquid, and had a sticker:


  MC-7 This fire extinguisher contains azeotropic chlormethanes®


Registered trademark symbol already signifies that marketing already prevailed at that time. Indeed, among chlormethanes $\ce{CH_xCl_{4-x}}$ chloromethane $\ce{CH3Cl}$ is flammable. Dichloromethane $\ce{CH2Cl2}$ is not combustible itself, but supports burning and flashes. Both chloroform $\ce{CHCl3}$ and $\ce{CCl4}$ are not flammable, but don't form azeotrope and still would produce phosgene $\ce{COCl2}$ when react with atmospheric oxygen. Also, the company denied presence of $\ce{CCl4}$ in MC-7 (Kiplinger's Personal Finance, Oct 1956, p. 48):


  CM-7, which has replaced carbon tetrachloride in all our grenade extinguishers. CM-7 does not produce toxic gases. It converts toxic gases created by the fire itself into additional fire-extinguishing chemicals.


As it seems like Red Comet doesn't hold any patents for inventions in chemistry, most likely it's a hydrochlorofluorocarbon that's been known at that time.

These days MC-7 extinguishers are sold as vintage items, and uniformly it's claimed (e.g. here and there) that the liquid component is 1,1,2-Trichloro-1,2,2-trifluoroethane, which at that time indeed has been studied as a very unreactive (even upon heating) vaporizable liquid agent (e.g. Fire Research Abstracts and Reviews, Vol. 3
1961, p. 148).

Starting 1960s, several acts in Montana, Chicago, and later across US no longer permitted usage of both tetrachloromethane and MC-7 as fire-extinguishing chemicals. Halons took over.