The Omni Weapon is an object that is capable of molding itself to any weapon the user desires - with two limits. The first being that the user must understand how the weapon he desires would work; if you don't understand the science behind the weapon you wish it to mold into, then it can't change into it, as it takes the design from your own mind. That doesn't mean you have to design it in detail, but you have to understand it. 

Thus a modern soldier could mold any kind of modern weapon, even if he isn't a weapon crafter - and weapons of a similar nature. However, he cannot make, say, a plasma rifle.

The second is he must have the ability to control the weapon with his willpower; this is simulated with the Absolute Concentration limitation.
 
Omni-Weapon
(Based off Cosmic Power) [ADRU]
++Indestructable [+3/6/12]
++Endless [+2/4/8]
**No Willpower Cost [x2] [subtotal: 20/40/80]
--Focus [-1/2/4]
--Accessible [-1/2/4]
--Immutable [-3/6/12]
--Irreplacable [-3/6/12]
--All powers must have attacks quality [-1/2/4]
--Absolute Concentration [-3/6/12]
--Restricted by Concentration pool (both dice type and
dice ammount used by this power cannot exceed the dice
for your concentration check) [-3/6/12]
--Must Be conceivable by user [-1/2/4] USer must be
able to conceive of the weapon or it cannot be
replicated
Total: [4/8/16]

Total Dice: 10wd
Total Cost: 160

This weapon, thus, being used by a guy with Cool 4 and Stability 4 could use 8 regular dice from the omni weapon - and of course, you have to perform the multiple action with concentration.