Nice double post.
No one mods the Ultimator to shoot smaller darts because that's not what the Ultimator is for... you use it if you want your enemies to think "wtf who just threw a shoe at me?" (GunnedDown) The ammo size is the key ingredient, not to mention the badass feel of the thing.
The Maximizer (little brother of the Mattel Ultimator) also used a racheting cocking system that was copied for use on the Max Shot. Interestingly, the Mattel blasters were the only 2 that I can think of that used an expansion spring rather than a compression spring to power it.
edit: just buy a $7 Super Soaker if you want to have to "pump" a big powerful gun to prime it. Just to satiate your curiosity, you could use a series of coupler reductors to fit PVC over the barrel. No, you CANNOT cut down the Ultimator barrel at all. The expansion spring stretches all the way from the tip of the barrel.
Edited by Jangadance, 18 February 2006 - 03:23 AM.