HOW does one "saw off" a "military assault weapon"? Assuming the media moron is referencing a modern battle rifle, sawing it off would have the effect of disabling the gas system. It would be a single shot repeater. Not too scary. Having shortened a modern battle rifle, I can assure the media that it is an involved and exacting task not accomplished without considerable knowledge, skill and specialized tools. Nitwit urban playaz wouldn't have the faintest idea how to begin.
Doesn't necessarily mean it was shortened at the barrel end. It might have the stock removed and replaced with a pistol grip.
There's also stuff like the Sig Sauer 556 Pistol .