Another question from a flashbulb novice. I have a small stash (2 dozen) of no. 25 M-class bulbs. My Pacemaker 4x5 has a Supermatic (X) shutter with a solenoid.
I've posted before about calibrating the solenoid for M-class bulbs, and found out that's something I'd rather not try (flashbulbs being so expensive). To my surprise I found on the box the flashbulbs came in the info that you can use these M bulbs with an X-synch shutter at 1/25 second (and I imagine slower).
Can anyone confirm this? If this is right I'm all set.

You're correct. It takes about 23 milliseconds for the bulb to reach it's peak output. That's just about what it takes the shutter to fully open at 1/25. Since the exposure is determined by aperture for the most part, you should be okay in dim light or darkness. For fill flash in sunlight you would normally set your aperture for the flah and the shutter for the ambient light. I'll let you figure out if that will work with X sync. Good luck.