unless you have expertise in assembling one, you're FAR better off with an already assembled gun- a lot of the kits are only machined to be "in the rough" or are simply parts thrown together- on the barrel link alone there's at least 3 sizes that i've seen personally- get anything that doesn't exactly "mesh" and you end up going to a smith anyway- with a factory gun, everything meshes , and it's been at least test fired , so you're starting off with a known quantity