The only disadvantage to Welch type plugs is that they're only available in steel, which rusts out. I've been tinkering with an idea to make a set of forming dies so I can fabricate brass plugs of the same design, using an arbor press or a hammer and anvil. 3/32" brass flat stock is available, and it would just be a matter of getting the right dome shape formed to make it expand and seal properly.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!