[Smith & Wesson Man]

I have a threaded 58cal breech plug, but I can't get threaded nipple out of it. I think the old owner never took it out. You can take the breech plug out with turning the nipple. I picked up a 209 conversion nipple for it, but I can't get that old one out. What can I do?

[arcticap]

Have you tired submerging it in good penetrating oil for 2-3 days?
Also put it in boiling water and then try to loosen the nipple while it's still hot.

[Smith & Wesson Man]

I have tried hot water for a few minutes, but not the oil. What kind of oil should I use?

[mete]

WD-40 or Liquid Wrench are designed as penetrating oils.Be patient ! Then if it needs help , apply heat with a propane torch .

[arcticap]

There are more ideas in this thread, PB Blaster is mentioned as is putting it in heated transmission fluid.

http://thehighroad.org/showthread.php?t=238579&highlight=%22penetrating+oil%22

If you do an advanced search for "penetrating oil" using the search function above, you should find more suggestions.

[Smith & Wesson Man]

I got it. Soaked it in WD-40 for awhile, and I grabbed one of those rubber wrenchs and finally got it off. Man it was dirty. I cleaned it out which took me about five minutes. Thanks for the suggestions everyone!