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texas1138
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Posted: 11/20/2008 7:01:34 AM
Anyone know where I could find blueprints or CAD drawings of an 80% lower? I know CNC has the 100% drawings. However I'm not sure exactly were it becomes 80%.

shrikefan
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Posted: 11/20/2008 7:48:14 AM
http://www.ar15.com/forums/topic.html?b=1&f=5&t=785523

http://www.ar15.com/forums/topic.html?b=1&f=5&t=787412

These may help.
TxTech0011
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Posted: 11/20/2008 10:58:04 AM
Im working on trying to produce a lower with a CNC machine and came across alot of different models available for download. Gotta put my plans on the back burner for now til after finals though. He is a good site.

http://www.cncguns.com/projects/ar15lower.html

http://www.cncguns.com/downloads.html
CBR900
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Posted: 11/20/2008 12:11:01 PM
"80%" is, and always has been an inaccurate description. BATFE does not use the term and its also being re-defined all the time.

As for the latest interpretation, from 2008 and directly from BATFE, this appears to be it:

"Here is the new "standard" for 80% AR-style receivers.

"Our Branch has previously determined that dimples or other indexing marks for pivot pin holes are counted as if the holes were fully drilled. Additionally, we have previously found that if any portion of the trigger group cavity area of an AR-type receiver has been milled (regardless of whether or not pivot pin holes are present), then that receiver-blank can be recognized as a "firearm" frame or receiver."

Source: FTB Letter 903050:MMK 311/2008-650


CBR900
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Posted: 11/20/2008 12:17:59 PM
look you asked about CNC code & such. Sounds like you have access to a CNC.

Do you want to be sure your piece is "less than a complete" firearm? Really sure? Really really sure??

There is only ONE totally risk-free way: follow the above letter as best you can, and then SEND YOUR TEST PIECE TO THE TECH BRANCH OF THE BATFE.

Sorry if that seems dramatic, but I believe this area is getting more & more scrutiny; I do not think that will change for the better in the near future. In fact, I think things will get worse, as they often do.
Leon82
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Posted: 11/20/2008 12:42:12 PM
if the lower is for you, you can use any print. even for 80 percent the print is the same you just dont machine areas so the atf is happy.
texas1138
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Posted: 11/23/2008 10:14:25 AM
Originally Posted By CBR900:
"80%" is, and always has been an inaccurate description. BATFE does not use the term and its also being re-defined all the time.

As for the latest interpretation, from 2008 and directly from BATFE, this appears to be it:

"Here is the new "standard" for 80% AR-style receivers.

"Our Branch has previously determined that dimples or other indexing marks for pivot pin holes are counted as if the holes were fully drilled. Additionally, we have previously found that if any portion of the trigger group cavity area of an AR-type receiver has been milled (regardless of whether or not pivot pin holes are present), then that receiver-blank can be recognized as a "firearm" frame or receiver."

Source: FTB Letter 903050:MMK 311/2008-650




ok so no pivot pin holes and no trigger group cavity.....
CBR900
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Posted: 11/23/2008 4:52:55 PM
Essentially, yes. And do not mark or "dimple" the locations of the required holes.

BTW, I encourage any other CNC machinists to follow the above letter, and start cranking out as many partially complete lowers as possible before the inevitable happens.
texas1138
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Posted: 11/23/2008 5:48:52 PM
Originally Posted By CBR900:
Essentially, yes. And do not mark or "dimple" the locations of the required holes.

BTW, I encourage any other CNC machinists to follow the above letter, and start cranking out as many partially complete lowers as possible before the inevitable happens.


I assume you can still drill out your hole for the selector switch?
kychas
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Posted: 11/24/2008 11:34:55 AM
I think the letter is for "for sale" 80% lowers and home build is not addressed.
the machinist normally do not need 80% lowers.
shrikefan
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Posted: 11/24/2008 11:48:06 AM
"Firearm frame or receiver. That part of a firearm which provides housing for the hammer, bolt or breechblock, and firing mechanism, and which is usually threaded at it's forward portion to receive the barrel."

Buy the regulations you could do everything except mill out the FCG pocket and it would not be considered a firearm. But since when has the .gov let laws and regulations guide anything they do or say.

Just make 100% SIG 556 lowers and sell them FTF, through the mail, etc..
CBR900
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Posted: 11/24/2008 4:14:45 PM
Originally Posted By kychas:
I think the letter is for "for sale" 80% lowers and home build is not addressed.
the machinist normally do not need 80% lowers.



Yes that is what I understand too.

Just be aware that when you get to the pojnt described in the letter, it is a firearm whenther it works or is complete - or not.
CBR900
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Posted: 12/12/2008 5:44:18 PM
BTT for info on new standard to follow if buying an 80%. (Better to start from 0%).