Found this iron pear shaped flask. Originally thought it was a canteen with a pewter flask, but the pear shape made others think it was a powder flask. The canteen is threaded on the inside. What is it? Canteen, powder flask, whiskey flask?
I think that was the way powder came when it was purchased from a company like Dupont or Hazard, you then used it to fill your own flask. Notice the screw threads inside the neck. No measuring device. A lead cap would have screwed in to it. The caps are often embossed with the company name. Older ones from 1850s-early 1860s had no threads. I think this one is from late 1860s-1870s. Perhaps someone else can help dating it.
As far as gunpowder never being kept in cans, just google images for 1860 gunpowder can, you'll see many examples.
That's why the neck and cap are lead.
I have antique powder cans that powder was sold in, and I have several found rusty cans that powder was sold in, one even still had powder in it. However I liked Reds post figuring that they didn't sell powder in flask shaped cans, then I found the picture, in my own saved photos, of a flask shaped can, so I un-liked Reds post, because it's wrong. I have diabetes, and my feet are numb, and apparently that malady is migrating up to my skull. Here is the picture of the can.
And I own a can like this one.
And here are two more different cans. And finally artifacts I found, showing two rusty powder cans, the one behind the spur is about half full of powder.
BosnMate showed you in his first picture a pear shaped steel can. Regarding another poster's statement that cans were "tin" rather than steel, tin is a misnomer, as in fact all tin cans are steel with just a coating of tin over them. In other words, they are not made of tin, they are made of steel.