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 thing about Optimus Prime's G1 and 2 toys was that the hands could not hold the photon rifle by the handle, instead being held by the ammo casing.

References

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