Open sockets can work for weapons, and for tools for heavy-duty cutting and chopping. However, an open socket isn't as strong, and the socket walls will need to be thicker, compared with a socket welded closed. Which will make the head heavier, which is not always desirable in a weapon. But open sockets are common enough on African spears, and Dark Ages European spears.
The relevant page, with picture: http://books.google.com/books?id=AS...g=PA87&lpg=PA87
One way to check whether a possible lance head is a weapon or a tool would be to test the hardness of the iron/steel. If it's hardened steel, it isn't an ox goad. Of course, some weapon heads weren't hardened steel, but good lance heads tend to be. Without actually testing the hardness, there can be clues: if it's made in two pieces, with a point welded on to a base and socket, there's a good chance it's a hard steel point and an iron base.