In equipment_missions.ufo the comment says

> // 1b. Select an ammo:<BR>
> // There is an equal probability to get any ammo in equipment definition that fits the weapon obtained in 1.a.<BR>
> // The number of ammo added (weapon being already loaded) is the number entered in equipment definition.<BR>
> // Note that writing 'plaspistol_ammo 0' is not the same than writing nothing: in first case weapon will be<BR>
> // loaded, in last case it won't.<BR>

This:<BR>
<BR>
> item (plasrifle 100)
> item (plasrifle_ammo 1)
<BR>
correctly always gives a Plasma Rifle which is already loaded and an additional ammo.<BR>

If I understood the comment correctly, this<BR>
<BR>
> item (plasrifle 100)
> item (plasrifle_ammo 0)
<BR>
should give a Plasma Rifle which is already loaded, but no additional ammo, while writing<BR>
<BR>
> item (plasrifle 100)
> // item (plasrifle_ammo 1)
<BR>
should give a Plasma Rifle without any ammo.<BR>
<BR>
Right now, while the first case (standard) works fine, in the latter two cases the alien will simply get no Plasma Rifle at all.<BR>