There seems to be an issue with unlocking the anti barrier sidearm rounds in the artifact.
Going through the steps i have now reset my artifact 4 times and i unlock the anti barrier sidearm first and continue through the other mods i want but when you close the artifact interface/screen it deselects the anti barrier sidearm and does not refund the unlock point.
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It's currently disabled due to bug. https://twitter.com/BungieHelp/status/1530407271309508608