Instructables
video Ferrocerium Incendiary Targets
Simple instructions on how to create some targets using ferrocerium to create a reactive effect when struck by a bullet.
Kiteman2 years ago
Two questions:

Can those rods be sawed into short lengths?

Does an airgun pellet carry enough energy to strike up a similar flash?
FPSoutback (author)  Kiteman2 years ago
Yes its quite easy to cut with a hacksaw, but as said you will get a load of hot sparks. It snaps easy as its brittle.

I don't know about air rifle, I think you will get sparks but not in a spectacular fashion. Steel BB's would likely ricochet quite hard. The idea is to shatter and powder the rods in the air then let pyrophoric oxidation ignite the powder.
@Kiteman to answer your questions:

"Can those rods be sawed into short lengths?"
I would say, No, as they produce sparks at temperatures at high temperatures. (as when scraped against a rough surface, like a saw blade)

"Does an airgun pellet carry enough energy to strike up a similar flash"
I think it would depend on the type of pellet. Using "traditional" BB pellets
(Usually made of steel and plated either with zinc or copper), I think it would be possible. Also it would depend on the firing method, many "airsoft" guns are either spring powered, (Automatic ones have a electrically driven spring system) or are gas powered (usually CO2)...
CO2 generally yield a higher FPS (foot-pound-second).

Your best bet would to just test out some of the options, though I would also look into the various methods used in "potato" cannons, some of them yield very high FPS.

Resources: (from Wikipedia)
Ferrocerium
Airsoft guns
Potato "gun" (they're actually cannons)

Good Luck, and Happy Testing!
(and welcome to the Aperture Laboratory Testing Facility)