Excellent news, Guardsmen!
Whilst purging a Hrud infestation on the Departmento Munitorum moon vault of Yurohubb Secundus, a Militarum Tempestus fire team encountered a cache of cataclysm-grade munitions that appear to have been stored there since the Great Crusade. Among them was a stash of Nihilus-pattern Vortex Grenades!
The good news is that, after much deliberation, Imperial High Command has granted you the honour of undertaking a field test of one of these deadly munitions against the Emperor’s enemies as a reward for your regiment’s outstanding service record.* As such, you shall soon receive one  Nihilus-pattern vortex grenade.
Upon delivery, pay no heed to the ‘Use Before’ date stamped on the side of your vortex grenade’s crate.** We have been assured that there is no plausible risk.*** After all, faith, the proper application of sacred unguents, and the singing of sacred hymns can compensate for anything the meagre ravages of time can offer up.
Nonetheless, to ensure that all other relevant safety protocols are properly adhered to, you are instructed to consult this antiquated user’s guide before use, and follow it to the letter:****
++ Thought for the Day: The universe is a big place, and whatever happens, you will not be missed. ++
* Your regiment’s long record of cowardice in battle has been officially wiped for the purposes of this mission to avoid a sense of expendability.
** This is actually the ‘use by’ date of the crate itself, and therefore irrelevant to this field test.
*** Doubting the integrity of your equipment is a floggable offence.
**** Failure to do so will result in a severe flogging… and likely the obliteration of your regiment by a swirling interdimensional vortex.