I'm in the process of refurbishing a 1913 trench style watch. The spring was needing replaced but unfortunately the new one from the suppliers had the wrong fitting at the barrel end. Due the cost of postage to return it, I thought I would modify it to fit the watch.
A few years ago I purchased an old spring punch, more because I like buying tools rather than I thought I might need it. I had a practice run on the old spring (the one in the photo) and annealed the end before using the punch. The result wasn't to good, so I tried it again without annealing and got the result you see in the photo. I now snapped the end off the new spring and punched a neat hole in it. Bearing in mind that the spring is only 1.3mm wide, I was well pleased with the result.
If you get the chance to purchase one of these punches at a good price, I would recommend you buy it.