Started over the last couple of days on a  15 build. I am using a SGT Freedom 80% lower a ?flattop upper and a CNC gunsmithing jig for the holes.Tools are  basic hand tools,dremel and a dril press .i have been using the builder squad project  info page for  starting this.  So i  have been working on the lipstick/file to fit lower to upper stage ,and i have the following problems.

1]At the rear of the lower where the buffer tube is tapped in,there is a flat plane on the top of this.When i have the upper mounted,i have a rise of 1.5mm appx on the upper where the charging handle  goes.Are these two surfaces supposed to be flush?I dont want to remove any more metal as I already have a gap in the rear curvature of appx 1 piece of paper[dunno what that is ,i dont have a feeler gauge small enough to go in.] It isnt bottoming out with the rear takedown pin lug either.
2] Drilled the fnt takdown pin  holes in the jig.when the upper is installed i have a gap  as well on the ejector side of again  1 piece of paper.On another board it was suggested to ream  the holes[done, and use a larger pin].The pin supplied with the lower kit now slides/falls out with no problem.Where do i get a larger pin?Also  I have light showing thru in some parts of the upper/lower mating.iwant to keep the tolerances as good as possible.Will this gaping affect the workings,ie dust & crud or have I screwed this up badly and would be better off getting another lower and start again? Or i was thinking of rebuilding the lower where it is gapping with chemical metal and using the upper to impress on the lower,remove and then refile to fit?

help!!!hinking.gif
Thanks
Irish

Heres some more good reading on machining lowers.

http://www.5bears.com/sta/stage2.htm

http://users.wfeca.net/rbrandes/ray-vin/disclaimer.htm

http://www.biggerhammer.net/ar15/cad/ar15_receiver.pdf

The third link is the most important. Its the blueprint for the lower just in case you don't already have it.
As for the upper to lower gap, not too critical. Sounds like you took a little too much off the top plane. As long as your pivot and takedown pin holes were located correctly the rifle should function fine. Just a cosmetic blemish you can fix by building up the top plane if you feel the need.

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