- Joined
- Aug 4, 2015
- Messages
- 291
Saw this pop up so I figured that I would through in my two cents.
If you have a mill and a lathe, you are way ahead of most people that are playing with the 80% lowers.
THe available jigs are meant to be used to complete a lower with a drill press and a positioning table sold at harbor freight and not a mill.
The lowers don't have the milling completed for the fire control group (trigger mechanism). The jig allows the person completing the lower to drill multiple holes at a controlled depth into the area being milled out and then with a 1/4 mill to cut between the holes to open up the area. Of course with a proper mill, you can just mill the area out. The second thing you need to do is drill the lower for the two pins that hold the fire control group in place in the well. The placement of these holes is very critical as they position the hammer and trigger sear engagement. Having these loose or in the wrong place can result in anything from a gun that don't shoot to a runaway where the gun goes full automatic with no control until you either dump the magazine or drop the magazine out of the gun. Having an AR-15 go into run away is some scary stuff if you are not expecting it.
As far as the jigs specifically. Buy one. Biggest reason for a jig as opposed to just getting an 80% lower and milling it to the spec you can find on the internet is the fact they are perfect for clamping the lower into the vice for milling operations. Trying to clamp irregular items into a vice can be an interesting proposition. Add to that the item is hollow and can be crushed, the jig is really the way to go.
Two pieces of advice.
One is if you are getting your diagram off the internet KNOW what you are getting. The diagrams are out there for both the AR-15 and the M-16.
The M-16 diagram is different. The most obvious difference is a third hole for the trigger group. That third hole is for the autosear parts that make it full auto capible. DO NOT EVER drill that third hole. That third hole makes your lower a machine gun in the eyes of the ATF and can result in going to prison, having all your guns taken away and all sorts of other bad stuff. They refer to drilling that hole as intent to construct. They get all crazy about that. There are some other differences but that third trigger group hole is the main one.
Other piece of advise for the budding gunsmith doing his first 80% lower dry fire it multiple times. Dry fire it and then with the trigger pulled cycle the bolt, release the trigger and pull it again and verify the hammer drops again. And the first few times you live fire it, load it with a maximum of 3 rounds. This will ensure that if something is wrong withthe hole placement or anything else that it can not fire more than 3 rounds if it goes into a runaway situation.
Have fun and be safe
If you have a mill and a lathe, you are way ahead of most people that are playing with the 80% lowers.
THe available jigs are meant to be used to complete a lower with a drill press and a positioning table sold at harbor freight and not a mill.
The lowers don't have the milling completed for the fire control group (trigger mechanism). The jig allows the person completing the lower to drill multiple holes at a controlled depth into the area being milled out and then with a 1/4 mill to cut between the holes to open up the area. Of course with a proper mill, you can just mill the area out. The second thing you need to do is drill the lower for the two pins that hold the fire control group in place in the well. The placement of these holes is very critical as they position the hammer and trigger sear engagement. Having these loose or in the wrong place can result in anything from a gun that don't shoot to a runaway where the gun goes full automatic with no control until you either dump the magazine or drop the magazine out of the gun. Having an AR-15 go into run away is some scary stuff if you are not expecting it.
As far as the jigs specifically. Buy one. Biggest reason for a jig as opposed to just getting an 80% lower and milling it to the spec you can find on the internet is the fact they are perfect for clamping the lower into the vice for milling operations. Trying to clamp irregular items into a vice can be an interesting proposition. Add to that the item is hollow and can be crushed, the jig is really the way to go.
Two pieces of advice.
One is if you are getting your diagram off the internet KNOW what you are getting. The diagrams are out there for both the AR-15 and the M-16.
The M-16 diagram is different. The most obvious difference is a third hole for the trigger group. That third hole is for the autosear parts that make it full auto capible. DO NOT EVER drill that third hole. That third hole makes your lower a machine gun in the eyes of the ATF and can result in going to prison, having all your guns taken away and all sorts of other bad stuff. They refer to drilling that hole as intent to construct. They get all crazy about that. There are some other differences but that third trigger group hole is the main one.
Other piece of advise for the budding gunsmith doing his first 80% lower dry fire it multiple times. Dry fire it and then with the trigger pulled cycle the bolt, release the trigger and pull it again and verify the hammer drops again. And the first few times you live fire it, load it with a maximum of 3 rounds. This will ensure that if something is wrong withthe hole placement or anything else that it can not fire more than 3 rounds if it goes into a runaway situation.
Have fun and be safe
