Hello and welcome. First off, your post is a little non-descriptive but I’ll do my best to help you. For the future however please take the time to read this post for more information on how to get a repsonse. About the Scripting Support category
Anyway, manual welds are actually apart of the old system, and it’s recommended you use the new constraints system, so how do you do that? Well it’s actually easier than the old way! WeldConstraint | Documentation - Roblox Creator Hub is the new version of manual weld, and is recommended you use it instead. So how would that work? Simple!
local weld = Instance.new('WeldConstraint')
weld.Parent = workspace
weld.Part0 = projectile
weld.Part1 = hitPart
Hope this helped! Keep in mind both parts have to be unanchored for this to work.