Don't know if this really helps....but I heard something of charge time and welding....
At our signmaking shop we use this one to weld bolts, and stuff to almost any material....mostly aluminium
http://soyer.cc/de/index.php?option=...120&Itemid=163 ok....it's a german site
....but take a look....you'll find an aequivalent product in the U.S.....
It has a recharge time of about 5 secs.....to be honest it depends on your fingers, cause it's a "single-shot"....(don't know if these welders you talked about come with endless wire or somethin'
).....
But we "shoot" hundreds of bolts......even on smallest parts, without any problems....
Not cheap, but worth a calculation for peeps, who do the big jobs....
Greetinx Alex