Best way to open mainspring barrels ?

[mikepilk]

I've always opened barrels by pushing down on the edges until the top pops off.  I'm aware that this can lead to bowing of the lid, and I've recently had a couple where the lid was bowed out.

This should be easy to fix with a staking set, but I've found it fiddly to get the lid absolutely flat - and they are soft, I put a circular ring on one from a punch.
If not perfectly flat, the end shake is wrong, and the lid doesn't clip in properly. 

Maybe it's just my inability with the staking set, but it would be better to avoid bent lids in the first place.

So the question is, how to remove lids without pushing the barrel. I remember someone ( @nickelsilver ?)  mentioned a sharp strike was one technique.

Striking what with what - I guess the arbor with a little hammer whilst the barrel is in the palm ?

 

[nickelsilver]

I do a sharp smack on the barrel arbor for clock barrels, unless they have a good slot for a screwdriver, but even then sometimes the smack works better.

 

For watch barrels I press on the teeth (unless there's a notch for a screwdriver, but even then...). Rarely an issue. But, I read on another forum where a highly regarded pro uses canned compressed air. He shoots it right where the arbor comes out, and apparently enough gets in to pop the cap (keep it captured!), with no distortion ever. Been meaning to pick up a can and try.

[mikepilk]

4 minutes ago, nickelsilver said:

For watch barrels I press on the teeth (unless there's a notch for a screwdriver, but even then...). Rarely an issue. But, I read on another forum where a highly regarded pro uses canned compressed air. He shoots it right where the arbor comes out, and apparently enough gets in to pop the cap (keep it captured!), with no distortion ever. Been meaning to pick up a can and try.

I think I'll give that technique a miss - I've enough with springs pinging around