Not sure why you'd want an "80%" you have to finish, I don't recall seeing any with the Fed required markings? You can probably figure out the reason...
Just buy and DROS a finished lower, build CA compliant. The lower is considered the "firearm", so once DROS'd, you just add the rest of the parts (as long as they are compliant and you don't "accidentally" assemble a "banned" configuration).
Technically an 80% isn't yet a firearm (per ATF), so no DROS or markings required, but now if you finish one in CA, you have to apply for a CA serial # and have it engraved (CA is afraid of them "ghosts"!). So you're doing a lot of jumping through hoops for no really good reason.
Just buy and DROS a finished lower, build CA compliant. The lower is considered the "firearm", so once DROS'd, you just add the rest of the parts (as long as they are compliant and you don't "accidentally" assemble a "banned" configuration).
Technically an 80% isn't yet a firearm (per ATF), so no DROS or markings required, but now if you finish one in CA, you have to apply for a CA serial # and have it engraved (CA is afraid of them "ghosts"!). So you're doing a lot of jumping through hoops for no really good reason.

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