2fg and 3fg both work well in my Jeager. I do usually use 4fg because as mentioned, it flows best through one of them thar push-primer thingies. I also load my pistols with 4fg, so if I have a cap-n-ball revolver with me I can leave the priming horn at home and just use the pistol flask. If I still used 3fg in the pistolas, I would prime with it, as I can tell no difference between 3fg and 4fg as far as ignition time, in my rifle.
The only time I used 2fg to prime was when I was recently chasing a wounded bear through the brush, (and missed it TWICE) and I was loading directly from my paper cartridges, and I detected no difference, but I had my mind on other things and was not paying attention to ignition time, although it seemed perfectly normal. My Jeager is very fast, and it's kind of like shooting a percussion rifle or even a modern rifle. I certainly did not notice any delay in ignition.
Nothing un-safe about using a spoon to crush 2fg into a finer powder. Unless you smoke a cigar while doing it, it's not going to magically ignite. But, like everyone says, try 2fg in the pan and see how it works for you. Generally speaking, the difference between 3fg and 4fg as far as ignition time goes, is pretty hard if not impossible to detect with human senses. So even if 2fg is slower, you might not know it, or be able to tell.
But having said that, it's true that flintlocks can be quite different depending on the quality of the lock, size of the touch hole, etc. etc. and a lot of experimentation will be in order. At any rate, it certainly won't fail to fire with 2fg, and if it does, or you get a "clack-whoosh-bang" the problem lies not with the powder.