As the title, it is impossible to complete the reward track for arms week (unless you buy reroll chips) as hardware is not giving exp and the challenges wont give enough to reach past maybe rank 9-10.
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Hello there, Thank you very much for reaching out to us. I'm sorry to hear that you are having trouble completing the event. We've received reports of this issue and are investigating it further. For any updates on this issue, we recommend viewing our [url=http://www.x.com/Destiny2Team]X/Twitter page[/url] and our Patch Notes as they become available, posted on the [url=https://www.bungie.net/7/en/News]News page[/url].