I did it. just go to your save game, you should find this at (C:\Users\"your profile name"\AppData\Roaming\Running with rifles\savegames\"your campaign name") unhide all folders first.
Basically i just open the .person with notepad, and edited like this:
<person max_authority_reached="50.012535" authority="50.012535" job_points="1414.000000" faction="0" name="ANDREW MARTIN" version="66" alive="1" soldier_group_id="0" block="11 15" squad_size_setting="0" squad_config_index="0">
<order moving="1" target="530.983 0 629.363" class="2" />
<item slot="0" index="12" amount="1" key="xm8.weapon" />
<item slot="1" index="21" amount="0" key="medikit.weapon" />
<item slot="2" index="11" amount="4" key="hand_grenade.projectile" />
<item slot="4" index="-1" amount="0" key="" />
<item slot="5" index="-1" amount="0" key="" />
<stash>
<item class="3" index="18" key="vest3.carry_item" />
<item class="0" index="13" key="f2000.weapon" />
<item class="0" index="18" key="aks74u.weapon" />
<item class="0" index="56" key="barrett_m107.weapon" />
</stash>
<backpack />
</person>
i just type the name of the firearms in here :
<item slot="0" index="12" amount="1" key="xm8.weapon" />
yeah i did spawn with some cool gun. BUT
, when i put it on armoury it doesn't appear. so much different when i drive the cargo trucks and hit the armoury, and voila! there's some unique gun, it's automaticly registered to armoury or when i pick up stock weapon on other faction, it would registered on armoury too. My question is, is there some trigger to add some rare weapon to armoury? or else?
