[Abagail]

Possible solution:

pawn Код:

public OnPlayerUpdate(playerid)
{
    new cWep;
    switch(cWep))
    {
    case 0: return 1;
    case 16,17,18,39,41,42,43: {
        if(GetPlayerAmmo(playerid) == 1) gAmmo = 1;
        return 1;
        }
}

public OnPlayerKeyStateChange(playerid, newkeys, oldkeys)
{
    if(newkeys & KEY_FIRE && isValSlot(GetPlayerWeapon) && GetPlayerWeapon(playerid) > 0)
    {
        if(gAmmo == 1) OnPlayerAmmoEmpty(playerid);
        return 1;
    }
}
stock IsValSlot(weaponid)
{
    case 0: return 0;
    case 16,17,18,39,41,42,43:return 1;
    default: return 0;
}

Untested...