- Joined
- Aug 4, 2015
- Messages
- 291
OK. Things to be aware of. There are a couple (one specific) high tolerance measurement that can't be wrong. That is the pin spacing between the hammer pin and the trigger pin. Sear engagement on an AR-15 fire control groups is very touchy. Too close together and the FCG (fire control group) will bind and lock up. To o far apart and the gun could go into runaway. That's bad. Run away is when the gun is fired once and the hammer continues to fall on the firing pin over and over again without the trigger pulled (read that full-auto fire). It's a really dangerous situation if you are not prepared for it. It will scare the **** out of you when it happens and the only way to stop once it starts is either dump the magazine, or oddly enough pull the trigger. Pulling the trigger will engage the disconnector and stop the hammer from falling.
A better way is to avoid the situation all together. The way to do that is make sure that your pin holes are correctly placed. This can only be done with a full and proper blueprint. But make sure to use a correct blueprint for an AR-15 lower and not an M-16 lower. They are both available on the internet and there are differences. If you are building with a jig, it has to be verified to be correct.
Second is dry fire testing. With the firearm verified empty and a verified empty magazine (don't even have ammo in reach when doing this) put an empty mag in the firearm and cycle the charging handle. Pull the trigger and hold it. You will hear the hammer fall. While still holding the trigger in, pull the charging handle again. Once the gun has cycled you should be able to release the trigger and hear a click, then pull it again. It should then dry fire. If it does not dry fire there is a problem. The gun will quite possibly run full auto which is a huge issue. Figure out why the hammer was not retained by the disconnector. IF it does dry fire after the gun was cycled the second time, repeat the cycle of charging, pulling the trigger and holding it, cycling it again and then releasing the trigger and pulling it again to ensure that it works correctly every time.
Once you are happy with that, move on to a drop test. With the gun verified empty and a verified magazine empty cycle the charging handle and place the firearm on safe. Smack the butt of the gun on a solid object (don't beat the hell out of it but don't just tap it either). Verify that after several bounces that when you take the gun off safe and pull the trigger that it does indeed dry fire. When I say dry fire I mean you should hear the hammer fall. If you hear it fall during the drop tests or find its already fallen when you attempt to dry fire it after testing, there is an issue and you need to figure out why the hammer fell. If this can't be addressed you should consider the lower to be dangerous and destroy it.
Now, at some point you will get a hankering to build a lower from scratch. There are two things that you need to be away of. First is the number of holes in the side at the FCG. There are a total of 3 including the hole for the selector. Never have more than that. An M-16 (read full auto) lower has another hole between the trigger pin and the selector switch. This hole is to locate the auto sear. You can't have this hole in the lower legally. Simply drilling this hole even in the wrong location is called constructive intent by the ATF. It means that you were / are attempting to create an unlicensed unregistered full automatic weapon and they frown on that alot. A lot meaning 15 or so years in a federal prison. So no extra holes. Second thing. All AR-15 lowers have the area around between the FCG and the back of the lower narrowed to not allow the placement of an autosear in the location that it would normally be in if the lower was an M-16 lower. You don't want to machine that area out either, again it's constructive intent and a major no no.
When you obtain your blueprints, you will find them on the internet with a simple Google search. VERIFY THEY ARE FOR AN AR-15 and not an M-16. They are real similar and if you carve out an M-16 lower, it's gonna have too many holes and too wide a gap in the back.
To verify your jig to be correct measure the FCG holes and gap width is what's on the blueprint, if it's not call the jig manufacture. Also, make certain that the lower does not shift in the jig when drilling and reaming the FCG holes by pinning the first hole before drilling the second hole. TEST your lower a lot before putting any ammo in the firearm. Once all the dry fire testing is complete. Begin live fire testing with 2 rounds in the magazine. Test the safety works when engaged, test that pulling and holding the trigger will only allow ONE ROUND to fire. You are gonna want to put 20 to 40 rounds through the gun 2 at a time like this so you are sure that everything is working correctly before throwing a full mag in the gun. Safety first. Any machining is fun. Being able to go out and fire a gun that you built from a block of metal is very fulfilling. But be vigilant about being legal.
I have read some comments in here that are great stuff. Creating and engraving a serial number in your creation is a good idea. Having an unserialized firearm of your own making is legal. But local police types don't always know this. A simple traffic stop during a range trip may get weird if you have a gun with no numbers. Allowing a friend to use your mill to build a firearm is sort of a grey area, but the minute you so much as turn the mill on for them, you cross a line. Use of your equipment by them should be cleared by the local ATF office. They are actually friendly folks for the most part and field all sorts of questions on a daily basis. They don't want you doing it wrong any more than you want to do it wrong, so talk with them. They are the ATF and they DO have all the answers. Legal questions on guns should only be directed to them and ANY advice from ANY internet source that is NOT the ATF web site should be taken with a grain of salt, including mine. If you ask a question of them and they provide an answer, ask for it either in writing (they will email typically) or have them direct you to the specific ATF ruling number that applies to the question. Again, this is what they do, let them help you avoid problems.
(edited for grammar and spelling)
A better way is to avoid the situation all together. The way to do that is make sure that your pin holes are correctly placed. This can only be done with a full and proper blueprint. But make sure to use a correct blueprint for an AR-15 lower and not an M-16 lower. They are both available on the internet and there are differences. If you are building with a jig, it has to be verified to be correct.
Second is dry fire testing. With the firearm verified empty and a verified empty magazine (don't even have ammo in reach when doing this) put an empty mag in the firearm and cycle the charging handle. Pull the trigger and hold it. You will hear the hammer fall. While still holding the trigger in, pull the charging handle again. Once the gun has cycled you should be able to release the trigger and hear a click, then pull it again. It should then dry fire. If it does not dry fire there is a problem. The gun will quite possibly run full auto which is a huge issue. Figure out why the hammer was not retained by the disconnector. IF it does dry fire after the gun was cycled the second time, repeat the cycle of charging, pulling the trigger and holding it, cycling it again and then releasing the trigger and pulling it again to ensure that it works correctly every time.
Once you are happy with that, move on to a drop test. With the gun verified empty and a verified magazine empty cycle the charging handle and place the firearm on safe. Smack the butt of the gun on a solid object (don't beat the hell out of it but don't just tap it either). Verify that after several bounces that when you take the gun off safe and pull the trigger that it does indeed dry fire. When I say dry fire I mean you should hear the hammer fall. If you hear it fall during the drop tests or find its already fallen when you attempt to dry fire it after testing, there is an issue and you need to figure out why the hammer fell. If this can't be addressed you should consider the lower to be dangerous and destroy it.
Now, at some point you will get a hankering to build a lower from scratch. There are two things that you need to be away of. First is the number of holes in the side at the FCG. There are a total of 3 including the hole for the selector. Never have more than that. An M-16 (read full auto) lower has another hole between the trigger pin and the selector switch. This hole is to locate the auto sear. You can't have this hole in the lower legally. Simply drilling this hole even in the wrong location is called constructive intent by the ATF. It means that you were / are attempting to create an unlicensed unregistered full automatic weapon and they frown on that alot. A lot meaning 15 or so years in a federal prison. So no extra holes. Second thing. All AR-15 lowers have the area around between the FCG and the back of the lower narrowed to not allow the placement of an autosear in the location that it would normally be in if the lower was an M-16 lower. You don't want to machine that area out either, again it's constructive intent and a major no no.
When you obtain your blueprints, you will find them on the internet with a simple Google search. VERIFY THEY ARE FOR AN AR-15 and not an M-16. They are real similar and if you carve out an M-16 lower, it's gonna have too many holes and too wide a gap in the back.
To verify your jig to be correct measure the FCG holes and gap width is what's on the blueprint, if it's not call the jig manufacture. Also, make certain that the lower does not shift in the jig when drilling and reaming the FCG holes by pinning the first hole before drilling the second hole. TEST your lower a lot before putting any ammo in the firearm. Once all the dry fire testing is complete. Begin live fire testing with 2 rounds in the magazine. Test the safety works when engaged, test that pulling and holding the trigger will only allow ONE ROUND to fire. You are gonna want to put 20 to 40 rounds through the gun 2 at a time like this so you are sure that everything is working correctly before throwing a full mag in the gun. Safety first. Any machining is fun. Being able to go out and fire a gun that you built from a block of metal is very fulfilling. But be vigilant about being legal.
I have read some comments in here that are great stuff. Creating and engraving a serial number in your creation is a good idea. Having an unserialized firearm of your own making is legal. But local police types don't always know this. A simple traffic stop during a range trip may get weird if you have a gun with no numbers. Allowing a friend to use your mill to build a firearm is sort of a grey area, but the minute you so much as turn the mill on for them, you cross a line. Use of your equipment by them should be cleared by the local ATF office. They are actually friendly folks for the most part and field all sorts of questions on a daily basis. They don't want you doing it wrong any more than you want to do it wrong, so talk with them. They are the ATF and they DO have all the answers. Legal questions on guns should only be directed to them and ANY advice from ANY internet source that is NOT the ATF web site should be taken with a grain of salt, including mine. If you ask a question of them and they provide an answer, ask for it either in writing (they will email typically) or have them direct you to the specific ATF ruling number that applies to the question. Again, this is what they do, let them help you avoid problems.
(edited for grammar and spelling)
Last edited:
Steve Shannon 
