Well, they do make a lot of seed, but it would take years to get those into a decent sized bulb for flowering. If you feed them after they have died back, and again about this time next year they should come up again like other bulbs.
(I leave the withered seed heads on for a while because I like them, then I cut them off and stick them in a tall vase in the house. They are pretty.)

I just have 2 in a very large wooden barrel..looking at them now I think I should have just put 1 in...would I be able to move 1 carefully out for next year show or not?

Not just now, however careful you are, the growing plant will suffer. Two in a large barrel doesn't sound too overcrowded to me, but then I can't see it? If you decide to move one, you could wait until the whole plant has died back and dig the bulb up.

Ok thankyou for that Oj :)

Its the first time for me to plant Allium Globemaster too. So I appreciate your questions and the answers. I have planted 5 together but spaced them so that hopefully the flowers wont bump into each other. I am trying to create a drift of them. I think 2 will be ok in a barrel as I am only presuming that there will be one flower on each bulb, but I could be wrong.

Yes, Marion - one head per bulb, but quite big!

thanks again everyone :) good luck Marion !