May not be a new idea, but I love shooting rubber blunts at stumps and such.  I just switched to wood from carbon and was trying to figure out how to get adequate weight from a rubber blunt.  I shoot a 160 field point and broadhead.  A rubber blunt is approx. 100 grains.  What I did was take a dremel tool to a 125 glue on field point.  I cut the pointy end of the field point off just in front of the internal taper.  It was now basically a steel blunt, more or less, that weighed 80 grains.  I then glued the point onto a wood arrow.  Finally, slip the rubber blunt over the steel point and wahla, a 180 grain rubber blunt.  YEAAAAAAAA!

Bret

Or use an untapered arra, slip a .38 casing on it(65 grains) after filing the rim down, and then your blunt.

Even better, I have some .38's too.  You just may be a genius.  By the way, nice name.

Bret  

More of a copycat than genius in this case...  

or a 357 case over a 23/64 shaft.

Another idea, is to buy a regular steel blunt, can really crank out some weight in a hurry by doing it.