I never had occasion to try flashbulbs with the FP shutter of the "Pacemaker Speed" I used in college, nor the one now in my possession (acquired in the early '70s). We always used synchronized front shutters, with #5/#25 and later, M5 lamps.

The flashbulb information on this site reports that the #6 lamp cannot be used with the Graflex shutter because of the curtain's long travel time. Sounds reasonable to me...

...but what flashbulb CAN be used with the FP shutter??

Sounds odd to me. No. 6 bulbs are a slow peak bulb made specifically for use with focal plane shutters. I would just try one and see what it does.

Indeed; we firmly believed (though without any hard evidence) that a #6 would synch with the "Graphic" FP shutter. It might be interesting to scrounge up half a dozen and find out...

...the tiny AG1 lamps had FP burn characteristics, and I sometimes used them with a 35mm. "Exakta" when a fast shutter speed was necessary. I'd be amazed if they burn long enough to accommodate the travel-time of the Graflex shutter. But the #6 is a different proposition.

Some other bulbs that were made for use with focal plane shutters were:
G.E. Mazda No. 2A
Wabash No. 31
I have tons of flash bulb information hiding in my "library".
When I get some time and feel up to the task, I will try to dig through the stuff and put together something. That will surely be after April 15 ------

Right you are. I hunted up my reprinted "Pacemaker" instructions, and found that the 2-1/4x3-1/4 model will synch with #6 and #26 lamps at 1/1000 second (only). The 3-1/4x4-1/4 and 4x5 models require #31 or #2A lamps, which also can be used with the miniature "Speed" at 1/500 and 1/250 second.

Cress lists the #31s at $4.00 apiece. This is likely to make experimentation rather costly.

Flash powder, anyone?