so I went to fully upgrade my red death with an exotic shard purchased from xur and instead of upgrading it completely wiped it back to the beginning. And now it takes spin metal and before it used helium
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Xûr's Upgrade section is for upgrading pre-dlc exotic weapons, which had a maximum of 300 attack, to 331 attack. And while you upgrade a weapon, it's progress is resetted. See here for more information: https://www.bungie.net/en/Help/Article/12457