A while back I bought some plastic balls for use in target practice (as the ammunition, not the targets ).  I chose them because they were advertised as "low bounce", and I thought that would help minimize movement after initial contact with the target.

The balls are slightly smaller than a tennis ball and weigh a little less.  The problem is I actually find them to be too light.  I'm trying to add some weight and have filled three with silicone.  I bought a few tubes of silicone, drilled holes in the balls, and just filled them up.  I chose silicone because I didn't want the "filler" to be completely ridged.  I imagine that because it's inside a ball, some of the silicone may not ever completely cure.  But I don't think that should be a problem.

I like the weight of the filled ones much better.  They went from just over 50 g to around 125 g.

I have 12 of these plastic balls and am planning to do same with the rest of them.  Does anyone think there could be any problem using silicone as the filler?  Or have any other suggestions on adding some weight to a hollow plastic ball?

they'll probably bounce
the silicone filled balls, that is.

Just to follow up on this, not too surprising but the silicone worked great as a plastic ball filler.  They don't seem to bounce much differently.  But one thing did change.  I wasn't thinking about this, but with them being a lot heavier, when the target is completely missed they go a lot further.  I had to fight through some weeds to find one that flew astray