Is shooting lead pellets backwards bad?

All it is doing is affecting your accuracy. Shooting a pellet backwards will just cause the pellet to spin in mid air until it rights itself. By having the front solid and the rear hollow, fluid (air) dynamics will cause the heavier part to eventually wind up pointed down range. Furthermore, by not having the hollow section facing the air discharge port, it will not swell to fill up the barrel space and get the full effect of all the air and it will not leave the barrel as fast as if it were aligned properly. But I guess you are smarter than the engineers that designed these pellets.