As variants of the standard bolt (not special bolts):
Broadhead bolt: basically a jhp bolt; more damage but higher penalty vs armor
Bodkin bolt: basically a w2c bolt; less damage but better armor penetration
Since they aren't special bolts, you can use them with snipe, aimed shot, etc. This is assuming that infusion will make you use a "quiver" of loaded bolts or something; if it keeps underrails "all regular bolts loaded at all times", then you'd need some kind of bolt selection to activate
