As far as I am aware the only way to get that again is to re-level a warlock with the gunsmith and do it again. I suggest liberal use of the "R3" lock in the future it has saved many of my weapons.
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I honestly didn't realize what it was. I saw it as a fusion rifle and said, meh. I have a better one. so I thought. Clearly didn't see that last perk (face palm)
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That sucks man, sorry about that