I tried filing, but I couldn't find any decent files in town. The one I bought either couldn't remove any material or was having material removed from it (not hard enough). That, and I'm not so good with delicate work, as I tend to get impatient and remove too much material or damage areas I didn't want damaged. So I decided to try the alternative method.
Still haven't had a chance to take it the range. I think I will make a point of doing so either later today or Sunday. If it still has problems extracting, I'll have another go at it with the ironing tool.