The main reason why some cocaine burns more than other is because the cocaine has residual acid inside. When cocaine is proccessed, hydrocloric acid is used to turn the freebase into hcl (the shit you rail). Afterwards, it is washed, usually with acetone to remove the acid. This step is usually rushed and there will most likely be some acid left over in the cocaine. Believe me, the acid will eat away at your nose a hell of a lot faster than cocaine ever will.
As for railing pills, its safe, but you will have shit dried up in your nose the next day from the fillers.