Frank, that "plug" is the tail-end of the extractor. <img src="/forums/images/graemlins/smile.gif" alt="" /> You should be able to insert a small screwdriver into the groove and pry it out, or push from inside the ejection port.

Early BHP's had the same type extractor before the design changed to the external type.

You did real good there BTW. Since you have it apart, and want to shoot it, why not replace the springs with new ones. Any big gun shop in your area probably has them in stock, or GOOGLE Wollf Springs and order from them. Brownell's would be another place to order from.