There are many schools of thought regarding the world of silencers it seems Barry.
I've seen hair curlers and panscrubs used to great effect, washers and spacers, double foamed haircurler combinations and my badly drilled washers and 5mm ring spacers, which isn't to bad really.
There are some lovely engineered ones from uk Neil which comes with a lot of recommendations!
Drilling your own doesn't sound far fetched to me :-) but I'm no expert..
Weihrauch have a great review also.