Photon rifle

The gun is actually not what's badass about this pic.

Photon rifles are a common weapon used by the Autobot army. Transformers who use such weapons include Optimus Prime, Jazz, and Bumblebee.

Notes

One notable aspect about Optimus Prime's Generation 1 and Generation 2 toys was that the hands could not hold the photon rifle by the handle, instead being held by the ammo casing, and because the large rifle butt, the rifle could only be pointed at an angle.

References

From Teletraan I: The Transformers Wiki, a Wikia wiki.