There is a formula used for your companions to select their own weapons. The formula takes into account damage, accuracy, reload speed...several factors and most single barrels will lose out to multi-barreled guns, though not in all cases; there are some single barrels that will "win" and get selected by a character, but they are probably few.
You can disable the characters auto-selecting, and you will need to manually equip them. Requires both enabling the Equip button and disabling the function the characters will use to select their own.
Program\INTERFACE\items.c, change line 175 to:
SetNodeUsing("EQUIP_BUTTON" , true);
Program\characters\CharacterUtilite.c, change line 3162:
void CharacterCheckEquipAll(ref refCharacter)
{
return; //Add this line
if(!CheckAttribute(refCharacter, "id")) return;
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