The Sigma is pretty much a airgun firing 6 mm's airsoft ammo, being much more powerful than most airsoft guns I handled. Most likely, there are no available upgrades to the Sigma with the exception of a couple KWC parts that include a longer inner barrel and a suppressor. KWC also have spare magazines in the catalogue, as seen in the website, but these aren't available in the UK.

 

The energy level is far higher than reported. Rated 1.0 J in the box and slide, a small sticker inside point to 1.5 J and the chrono reports it even higher at 1.6 J. This represents near 415 fps with .2 g bb's and is more than acceptable for a close range backup gun.

As the energy level isn't variable, the gun keeps shooting between 1.5 and 1.6 until the canister start to be almost empty.

Specifications
Action Single Action *
Overall Length: 184 mm
Barrel Length: 114 mm (4.5in)
Weight: ca. 960 g empty
Capacity: 39 rounds