From VG247: “There are quite a few challenging hoops youll need to jump through to access the Volundr Forge in Destiny 2: Black Armory.
The majority of the activities in Black Armory require a Power level of at least 595 600 to do any real damage, as the Power cap has been raised to 650 in Season of the Forge. The level requirement was lowered by five points over the last week as many players felt Black Amory was inaccessible due to its high Power recommendations.”
Source: N4G PC Destiny 2: Black Armory – Machine gun frame and Volundr Forge guide