Cut the main panel then mocked a sidepanel in paper. Took a couple of shots to get right and next time I'd add ½" to the top curve so the folds came up a little higher in the throat.
Here's the template I cut to.
Worth pointing out that the holes for the drawcord are placed so that the folded edge is drawn in flush to the main panel. Nearly punched them evenly then realised that the folds would be sticking out.
Going to make a smaller one, pellet pouch size. I'll post up the template for that too if it works out ok.
Cheers for the comments.
Funnily enough Tam I was thinking of trying a wee belt pouch as well.