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Old August 25th, 2019, 04:43 PM #1
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First Poly 80 build:

I've been sitting on a Polymer 80 kit for about 3 or 4 years now. Never got up the time or nerve to mill it out, but finally did this weekend. Upper is a Doublestar HB carbine lenght with USGI milspec BCG. CMMG LPK with ALG trigger group and hammer. PSA Milspec buffer and rear-end. Magpul MOE grip, UTG BUIS.

Only issue is that the Magpul mag isn't tripping the BHO, but CProducts mags and USGI mags will. Not sure what the issue is there, but it's easy enough to just use the CProducts stuff (and cheaper!)

Milling was pretty easy. Used a HF drill press and Shop Fox cross-slide to do it all. Found out (as many others have) that drilling holes to the prescribed depth with a drill bit and then using the end-mill to take out the remaining material was the best way to go about it since end-mills aren't really made for drilling straight down. Kept measuring twice and cutting once and didn't have any issues. Seems really solid. No upper wobble, everything mates up nice and tight. Looking forward to putting some rounds down range with it and seeing how it performs. Now that I've done one, I feel pretty confident in tackling an AR10 next.


Last edited by tallen702; August 25th, 2019 at 04:44 PM. Reason: forgot pic. Doh!
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Old August 25th, 2019, 07:44 PM #2
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Looks good. I’ve got 2 poly and 2 regular lowers waiting to be built! You have provided some motivation
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Old August 25th, 2019, 08:04 PM #3
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Nice work! Whole thing looks great
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Old August 25th, 2019, 09:52 PM #4
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Quote:
Originally Posted by babalou View Post
Nice work! Whole thing looks great
Thanks! Only reason the receiver is FDE is that it was $10 cheaper than the black ones when I bought it.
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Old August 25th, 2019, 11:04 PM #5
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Poly build

It took me about 4 of those to get one that worked. I had one completely built and when using it, the pin that holds the buffer back broke. Actually the pin did not break, but the plastic assembly that holds it gave way.

I messed up the others with bad hole drilling and other stuff.

I did have to get retained pin sets as the pins kept sliding out of the lower.
It does seem to work now, but I do not use is often. I do not know how long it will hold up.
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Old August 25th, 2019, 11:58 PM #6
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First rule about poly80 is don’t talk about poly80. Welcome to the club, it’s pretty awesome to know “I build that”
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Old August 26th, 2019, 12:20 AM #7
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haha

Quote:
Originally Posted by tallen702 View Post
Thanks! Only reason the receiver is FDE is that it was $10 cheaper than the black ones when I bought it.
I have seen people pay extra for FDE.
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Old August 26th, 2019, 08:32 PM #8
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Quote:
Originally Posted by owgriffin View Post
It took me about 4 of those to get one that worked. I had one completely built and when using it, the pin that holds the buffer back broke. Actually the pin did not break, but the plastic assembly that holds it gave way.

I messed up the others with bad hole drilling and other stuff.

I did have to get retained pin sets as the pins kept sliding out of the lower.
It does seem to work now, but I do not use is often. I do not know how long it will hold up.
I wouldn’t use the buffer retainer pin on a polymer lower. Don’t need it. Just remember to catch your buffer when you open the halves. Those pins can break and cause issues as it is. The way the system works, that looks like a good way to crack or wallow out the plastic of the lower right there.

I leave mine out of my GWACS lower. I do use them in my aluminum lowers.
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