These booots, though useful, were originally created as part of a well-known bait-and-switch scam in the retailer shipping industry that frustrates thousands of I.T. specialists per cycle.
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Boot Loader
Wondrous item, technomancy, uncommon
You can rearm certain weapons by sliding them across specialized hooks and linear electromagnetic nodes on the side of these boots. While you wear these boots and aren't restrained, you ignore the Loading and Reload property of basic weapons with which you are proficient.
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Prosthesis Variant. This version of the item is a prosthesis instead of a wearable boot, which replaces a lost leg or foot. While you wear it, it functions identically to the lost body part. You can also attune to this prosthesis; if you do, it cannot be removed from you against your will and it grants access to an internal space that can store and conceal one basic weapon with the Loading or Reload property, which you can draw that weapon as part of an attack you make with it. This concealment can be discovered by a creature that uses an action to examine the prosthesis and succeed on a DC 15 Intelligence (Investigation) check.
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DESIGN COMMENTARY
The name is a play on the computing term.
This item has less to do with conventional technomancy than the others, but still has the tag because it is 1) meant to be a "smart" item and 2) shouldn't be available in a basic store. It fulfills a pseudo-Terminator fantasy in which a character reloads a weapon by doing something cool; in this case you hook it to the boot and reload it (loudly, presumably).
Its usage is very simple and offers enough given it has no attunement cost. The Reload property of futuristic weapons already have little effect in conventional combat. However, Loading weapons (typically crossbows and railbows) get to remove their Loading property. Despite 5e's restrictions and the existence of Crossbow Expert, the lack of Loading property doesn't change much because 1) crossbows are not much different compared to their shortbow/longbow counterparts, and 2) those only proficient with crossbows only benefit from a lack of Loading if they have a means to make extra attacks , which usually means they already have martial proficiencies.
Either way, I'm sure there's a way to exploit it, so keeping it at uncommon rather than common is fine.
If your character wears it as a prosthesis, you also get to attune to it, granting additional (but ultimately minor) benefits.