Good afternoon, again
As per basic rules all weapons have three firing modes - single shot/semi-auto and full auto. While single shot and full auto have obviously clear meaning, "semi-auto" is a bit confusing - what is it? IRL semi-auto weapons (like, for example, SKS carbine, Enfield L1A1 (British version of FN FAL) or M1 Garand) are capable of firing single-shots only (have no capability of firing in bursts or full auto), however the weapon uses recoil or gas engine to automatically self-reload until there are ammo left in the weapon's magazine.
And than we have the standard Imperial Guard's issue lasgun (M36 M-Galaxy short pattern) - that is said by canonical sources to be a select-fire weapon (like, say, an IRL AK-47) capable of shooting both semi-auto and full-auto ( http://wh40k.lexicanum.com/mediawiki/images/4/4b/Primer-19-lasgun.jpg - the proof is here), however, as per both Dark Heresy and Rogue Trader rulebooks lasgun have the capability of only "single shot" or "semi-auto". So the question is - what is the game's "semi-auto" actually - merely several single shots in quick succession by manually pressing the trigger each times, or it is a short "limited" burst of full auto fire, like the 3-rd burst mode on M16A2 or 2-rd burst mode on AN-94 Abakan?