Years ago, I bought a matched set of horns, Primary and an Priming horn, and each hung from its own leather thong over my neck and at my side, above or next to my bag. I looked pretty as a picture.
I do not regret buying the horns. What I do not like is the fact that I have to worry about the leather thongs coming off, and the horns banging into me, and other things. The horns are worn, with my buckskins, knife, and tomahawk, when my club is doing a public demonstration. I even remove my eye glasses, becoming a public menace in the process, just to give the tourists a " nice " picture.
Over the years, I have found that 3Fg powder works as well as Priming powder in my rifle, and better on rainy or foggy days. So, the priming horn gets left at home, or in the car. I have begun to leave my main horn in the car also, and simply carry pre-measured powder charges in plastic tubes when I am hunting. The same powder can be used for priming. And, the bag stays home, now, while I carry the needed items in the pockets of my various layers of clothing I wear anyway.
I have some small horns that I want to flatten, and make into pocket-sized carry horns, for hunting, with the idea of using them with a small caliber gun to shoot squirrels and rabbits. With the small caliber, powder charges will also be small, and the small flat horn should carry more than enough powder for a day in the woods. But, I can also use them to carry powder when deer hunting, as I never expect to get more than 2 shots on a deer hunt as it is. And, these small horns will carry enough for several more shots, if needed in a survival situation to signal to others for help.
The best use for those small " Priming " horns, in my humble opinion(IMHO), is to carry a small amount of powder - just enough of FFg or FFFg powder-- for use during a hunt. Find a pocket it fits in and carry it there. If you buy a flat horn, it can often fit in a back pants pocket, out of the way, but quickly available to you to reload your gun. I have put my round priming horn down my jeans back pocket when I used it to prime my fowler at a clay target range, but its a very uncomfortable place to carry such a style of priming horn.