I have a pinhole just like this with aluminum shim (is that the right word?)
I used the tip of a beading needle #10 or #13 (not sure which).
In bright sun, using RC paper, I get a pretty decent exposure at 60 secs.
If you used a finishing nail, I'm just going to guess (even with just the tip) that you have a way bigger hole.
Everything that Donald says above is exactly the things I had to go through in order to tweak my first tries- eliminating the obvious.
My oatbox is my favorite pinhole. I love the distortion, so go have fun with it!