I also like not having to attach a bunch of washers to the end of a piece of pvc. It is much nicer to glue a piece of flatstock inside of the core. However it does take some time to heat up and flatten a core.
Needless to say, there is nothing from our method here in N.O. that would prevent us from inserting counterweights into the core. In fact we were doing this back in the 1980's before we had even heard of WMA. We used to put railroad spikes in the handles of our weapons so they would handle better (people used to consider it 'cheating'!)
I occasionally actually do use some small carriage bolts under 4" to partially balance a sword today. However my friends and I found over the years that putting a rigid, heavy counterweight inside the PVC core tended to cause it to snap right at the point where the counterweight ended if it was longer than about 4-6 inches.
In the end, I am happy using the washers, they are easy to attatch and form the basis of a pretty nice wheel pommel. Also, in a real sword most of the counterweight is actually provided by the pommel itself.
Even breaking once in a while is too much for me, because I just don't have the bucks to keep shelling out for duct tape. Like I said, my padded wasters don't break. I haven't had one break in over a year, and I hit very, very hard. I'll put my krumphau up against anyones!
Ultimately of course, I don't mind if nobody else sees eye to eye with me on it. I'm glad to use my old method, maybe I'll try to incorporate shaped cores into it. There are many roads to salvation, after all! I'm just sincerely glad to see people continue experimenting.
DB