What should I use for filling B&W FS700 speaker stands (for use with B&W 705s)?

Hello all - I have a question that has paralyzed me up to this point.  I want to add mass to my FS700 speaker stands that support my B&W 705 speakers.  I want to make them less "tippy" mainly.  I am also concerned about adversely or positively affecting the sound quality with whatever I choose.  Lead shot is very expensive, but I am considering it.  Are there good alternatives I should look at?  Steel shot?  Sand (kinda messy)?  What about small landscape rock (1/2" or less)?  Any suggestions from this community would be most appreciated.  - Bob