If you’re trying to make the weapon for the newer N17 version then you’ve linked to the incorrect tool section. We have two sections, one for original Necro and one for the new.
Here’s the link for the N17 (also called ‘Underhive’ in the tools)
https://yaktribe.games/underhive
To create a custom weapon like a master crafted Lasgun, follow these steps-
Underhive tools >Customise >Custom weapon stats.
Click the blue ‘add’ button in the top right corner. From this drop down, we can create and name the weapon profile (for example, Master Crafted Lasgun), and input the weapon stats. These are the same as the normal weapon basically, as master crafted isn’t a weapon trait and doesn’t change anything about the regular weapon except for its price
[edit- since the House Of… book series, Mastercrafted is now a weapon trait].
Next we need to create the actual item, so we go to-
Underhive tools >Customize >Custom equipment.
Click the blue ‘add’ button in the top right corner. From this drop down we will create the actual item entry as it will appear in your weapons lists.
Name the weapon (Master Crafted Lasgun for our example), and calculate the cost (basic + 25%, rounded up to nearest 5. For a Lasgun, this means add 5 to its basic cost, so the total cost would be 10 for Escher if using their House list price, or 15 + 5 = 20cr if you don’t, or for any other house).
The ‘section’ drop down determines where this weapon profile will appear. Although it’s a status weapon, I would put it in ‘basic weapons’ but you can put it where you want. Remember though that this determines which drop down box you will find the weapon in when you try to add it to a fighter.
Set the weapons rarity, and then select the weapon stats. Look for your custom ‘master crafted’ version of the weapon. We could simply use the regular version of the weapon stats but if we do, the weapon won’t appear as ‘master crafted’ on the fighters card, though it will appear as master crafted on the detailed fighter screen.
Set ruleset to global, shared to ‘campaign’ or ‘friends’ as appropriate (this allows others you play with to use the weapon entry), and set the campaign availability restriction to ‘none’ if you want it to be available in all campaigns, or if it is a weapon specific to a custom campaign choose the campaign you want it to appear in.
And that’s it! The weapon profile will now be available to buy under whichever drop down you selected during the ‘section’ step.
Hope this helps!