I assembled the 516446780 rifle kit yesterday, but ended with an extra spring & detent (pictured close up). Everything otherwise moves like it should. My lower has a closed trigger guard so that packaging was unopened.
Where do these go?
That is your safety selector detent.
The spring without seeing them side by side, the spring is likely the safety selector detent spring, or the takedown pin spring.
My money is on the safety selector detent spring.
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PSA is also known to put in extras. 
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usually psa puts in an extra takedown detent and detent spring as they are most usually to be muffed up on the first try to novice builders especially on the front takedown pin. i’d be curious if you accidently put in the wrong safety detent versus a spare takedown pin detent.
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Thanks everyone for your expertise and quick replies.
Now that yall mention it, the Safety Switch does not feel as confident as it should. These must be for that, and I mistakenly used some extra parts in there.
After swapping in this spring & detent, the safety works much more decisively. I must’ve grabbed some of the extra parts accidentally.
Tons of lessons learned and great learning experience from the build and all the knowledge on this forum.
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no problem thats what we are here for, to learn to share, and have fun! glad you got it figured out! where are the photos of it?!?!?!?!
you’ll have to let us know how the bad boy shoots.
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Heh well the rifle is just the kit at the moment so not very photogenic yet, but when all the upgrades come in it will definitely get a thorough range day & photo shoot.
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All my kits came with 1 extra like you have there.
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Extras? no they are AR seeds.
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After your first few builds, you will need a designated parts box. I suggest you buy at least 2 “oops” kits because you will surely need them. I have saved myself and several friends from having a gun down for over a week waiting on a $2 part. Just be sure to replace any part used ASAP. I probably have $200 worth of AR parts on hand.
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I have no box of parts. Somehow a spring turns into a new gun…
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