Every item (including ammo) needs a tech, so, yes, you need to add a new tech entry (but you can create new ufo files for your new tech/items/wathever if you want), you might want to look at the assault rifle techs as an example, maybe you also want to take a look at researched_list.ufo
An ufopaedia entry isn't strictly needed, (but would be cool, wouldn't it?) you can write a short description if you like.