[Al Skierkiewicz]

Wow!
Here a few things for you to consider when contemplating ballast from an inspector standpoint.
1. Sand, don't think you can encase sufficiently that it won't pose some hazard. The capped steel pipe might work but... I had a team try to demonstrate sand as a hammer weight last year. When asked to demonstrate their containment they promptly broke the container and dumped several pounds of sand into their robot in the pit.
2. Shot of any kind must also be suitably contained. Plastic bottles do not fit that definition.
3. Lead, if your sponsor/build space/school allows you to handle it, must be fully encased and untouchable at competition. We have allowed lead to be painted and sealed with the understanding that it cannot be machined in any way at a competition. Many local ordinances and venues prohibit it's use.
4. To reiterate sash weights, you need to know the material as it varies in the part of the country you live and the era in which they were made. (See lead above)
In all cases, ballast needs to be firmly attached to the robot with fasteners. Ty-wraps, duct tape, etc. are not considered fasteners for this application. Personally I like big hardware with locking nuts.
R8 is pretty specific, if your ballast has the ability to come out of your robot and damage another robot, a volunteer, or the field (shot or sand dumped on the field comes under this heading) it violates R8.