I am not sure from your first post, are you using a copal 0 shutter?
I have used many of them over the last 4 years with a tech camera and before than on large format. You always have the T option. This option would be better for longer exposures in my experience. With the T option, you hit the shutter release once, and the shutter opens, then you hit it the 2nd time and it closes. The B option, you have to keep the pressure on the shutter the entire time during the exposure and this leaves to the chance of movement.
If you your shutter won't get the 1 second and B to work, then T might not either, but the shutter should work with this in 1 second. IMO that's not normal for a Copal. The shutters I have used, the B, 1 second to 30 seconds, are always pretty accurate, but above this, accuracy is not that great, 1/60 might shoot at 1/90th, etc. Most of the shutters I have won't shoot 1/250, ever, instead they hit 1/350th and 1/180th mark. Most times they hit 1/500, but I don't use that very often.
I would consider having the shutters worked by someone to see if there are any problems. If you are in the U.S, consider Precision Camera works in IL. They are on the web and can work over your shutters to see if they can get the lower speeds to work better.
You may also have a problem with your cable release, not making good contact on the longer exposures, and might try a different one just to see.
Paul
