On the little ones (50-ish cal or less) there is no other way to do it. A foil bag is just too small.
Do not pour directly out of a can or flask... dangerous. Pour into a measure first, and then pour from that. I use 25 ACP, 9mm, 45 ACP pistol cases alot for measures in the little ones.
At 1 inch bore a foil bag is practical, and speeds reloading time up considerably. An inner plastic bag at 1 inch is akward, but I use plastic bag inside foil for my 2.25 inch mortar.