I got tired of my foam chux being too light. I want to work on getting used to a heavier pair, so I decided to modify my foam ProForce chux by adding a little weight to them!

Here was my first attempt at weighting them, and it was... probably one of the dumbest ideas I've had in a long time. I guess I thought that little rubber cap would hold that heavy steel dowel while being swung around. I gave it one swing and the dowel flew out like a bullet. I'm really glad I had some common sense and tried this outside rather than in my room!
I decided to apply my experience with modifying my old cheapie foam chux (where I inserted a thinner steel rod perpendicular to the chuck tube, and used that to wrap the cord around to string them).

What I did here was cut a nail with bolt cutters, and filed the end flat with a bench grinder. The head of the nail would help keep the nail itself from somehow flying out. The metal dowel would be placed inside the chuck, and the nail would be used as a stopper to keep the dowel from flying out. I just had to cut the dowel roughly with a hacksaw, then use the bench grinder to make the dowel fit perfectly inside (there's only a little bit of rattling on one of the chux, otherwise they are a perfect fit inside)

There's the finished product with the cap and foam placed back on. The cap and foam also help make sure that nail's not going anywhere, and the dowel should stay safely inside during any practicing. The only issue is the cord I bought for stringing my chux isn't quite up to this weight, and after only a few hours of practice I see a little bit of fraying starting already. Looks like it's time to invest in some paracord! Hope this was useful to anyone.
Oh, and as a side note, the dowels take about 10 seconds to take out or put back in. they're not secured at the top (I haven't found that they need to be. The friction against the rope and the fact that the force being applied on them 99% of the time is towards the bottom means they don't need anything else to hold them up there) so all you have to do is pop the top off and slide them out!