Welcome to the forum. Thats a beautiful .30 commercial. You can find some Luger history here:
http://www.lugerforum.com/history.html
Your Luger, if completely matching, is worth around $1500 +/- ; more experienced members can give a better value estimate.
Almost all Luger parts are numbered though on a Commercial they are in non-exposed places. If you break a numbered part that will reduce its value considerably. I wouldn't shoot it without replacing the extractor, firing pin and original ejector with non-numbered spares. Spares are available from forum member LugerDoc and from Gun Parts corp.
Your Luger is a piece of history; even more so belonging to your Grandfather. Congratulations on owning a fine piece.
Charlie