jester_s1
Member
Disclaimer: I'm posting what worked for me and me alone. The information is free and might be worth exactly what you paid for it.
I have had an AR for a while and wanted a lighter, smoother trigger as many if not most do. My only problem is that I'm cheap. The issue with stock triggers is that they have lots of positive angle in the trigger/hammer engagement area that adds to the pull weight. The finish can also be rough too.
It's been covered numerous times online how to recut this angle, so I didn't take any pics for that part. Basically, all I did was stone the nose of the trigger to 90 degrees relative to the pivot hole, then I assembled the trigger and hammer using the holes outside of the rifle to check the fit. I then stoned a slight change in the angle of the hammer hook to match.
The only problem with doing this is that these are case hardened parts, and stoning away that material cuts through the case hardening. That was verified when I reassembled the rifle and dry fired a few times. The trigger felt good for the first 10-15 pulls, then started getting rough and mushy toward the end of the pull because of wear on the soft metal.
So I cleaned up the cuts again and rehardened the metal. I first contacted some heat treating companies to do it but they all made sure to price themselves out of the job due to liability concerns. So I went at it in the backyard. My reasoning was that I will discover a problem when I dry fire the gun if there is one, and if I still haven't hardened it up enough the trigger will get rough and mushy again long before it actually fails and causes doubling.
I packed the hammer and trigger in a steel can (green beans I think) with finely ground oak charcoal that I made on the grill. The can just needs to be big enough that the parts can be surrounded by charcoal and not touching the sides. I filled the can all the way up with charcoal, then sealed it with clay on the open end and put the metal top back on. Good case hardening depends on a no oxygen atmosphere for an extended period of time, so the sealing is the most important part. Then it was time for the heat.
These are the pics of my highly scientific super accurate heating apparatus.
It's basically a charcoal starter and a camping pump with a piece of steel pipe taped to it. I used to do blacksmithing and learned the basics of fire management and how to judge proper heat, and I knew that a pile of charcoal could get hot enough. The goal was to hold the can at 1700-1800 degrees for two hours. It's ok if it gets too cold during the process. You just extend the time to make sure you get that much time at temp. There will be no carbon migration below critical temp (around 1600) and if it gets up past 1900 things start melting (the can first, then the parts). In low light but not nightime, 1700 is a bright orange color, similar to how a sunrise looks when it's all the way up. The darker the ambient light, the brighter 1700 degrees will look. 2 hours at 1700 degrees should yield around 10 thousandths of surface hardening, which is very close to how these parts are leaving the factory. You maintain that heat by blowing air in from the bottom just like in a blacksmith's forge. You also need to have a small pile of charcoal getting ready to use when you start. Do not add fresh charcoal to the fire. It will suck the heat right out of it and delay the process. Get coals ready to use then drop them in as the fire burns down. Also be very gentle with the can once it's hot. At 1700 degrees, it is as fragile as tissue paper and if you move it around much as you add charcoal it will tear open.
I did the heat, and because of letting the fire burn down too much at one point it took 3 hours total to get the whole 2 hour soak done at heat. I then dumped the whole works out on the grill, and tore the can open and dumped it out in my wife's colander (she wasn't home!). I found that I had damaged the can during the heat by moving it, but I went ahead and seperated everything out and found the hammer and trigger and dropped them straight into my quenching water. I then did a 350 draw in the oven for an hour.
I had to do some very basic polishing to the parts after the process, and then I coated them with CLP since the original phosphate coating was long gone. I've done 100 dry fires so far with no change in the trigger feel. It's a smooth 4 pounds now and perfectly acceptable for my uses. I could get it lower with a reduced hammer spring or with one of the adjusters to remove sear engagement, but it's good enough for me now.
I'd love to hear from anyone else who does this. I can't say it was worth it just from a financial standpoint, because I could have bought the Bushmaster match trigger (trigger only) for about $40 and accomplished the same thing. But it was a fun experiment to do and I have kept all of the stock sear engagement so safety isn't a worry.
I have had an AR for a while and wanted a lighter, smoother trigger as many if not most do. My only problem is that I'm cheap. The issue with stock triggers is that they have lots of positive angle in the trigger/hammer engagement area that adds to the pull weight. The finish can also be rough too.
It's been covered numerous times online how to recut this angle, so I didn't take any pics for that part. Basically, all I did was stone the nose of the trigger to 90 degrees relative to the pivot hole, then I assembled the trigger and hammer using the holes outside of the rifle to check the fit. I then stoned a slight change in the angle of the hammer hook to match.
The only problem with doing this is that these are case hardened parts, and stoning away that material cuts through the case hardening. That was verified when I reassembled the rifle and dry fired a few times. The trigger felt good for the first 10-15 pulls, then started getting rough and mushy toward the end of the pull because of wear on the soft metal.
So I cleaned up the cuts again and rehardened the metal. I first contacted some heat treating companies to do it but they all made sure to price themselves out of the job due to liability concerns. So I went at it in the backyard. My reasoning was that I will discover a problem when I dry fire the gun if there is one, and if I still haven't hardened it up enough the trigger will get rough and mushy again long before it actually fails and causes doubling.
I packed the hammer and trigger in a steel can (green beans I think) with finely ground oak charcoal that I made on the grill. The can just needs to be big enough that the parts can be surrounded by charcoal and not touching the sides. I filled the can all the way up with charcoal, then sealed it with clay on the open end and put the metal top back on. Good case hardening depends on a no oxygen atmosphere for an extended period of time, so the sealing is the most important part. Then it was time for the heat.
These are the pics of my highly scientific super accurate heating apparatus.
It's basically a charcoal starter and a camping pump with a piece of steel pipe taped to it. I used to do blacksmithing and learned the basics of fire management and how to judge proper heat, and I knew that a pile of charcoal could get hot enough. The goal was to hold the can at 1700-1800 degrees for two hours. It's ok if it gets too cold during the process. You just extend the time to make sure you get that much time at temp. There will be no carbon migration below critical temp (around 1600) and if it gets up past 1900 things start melting (the can first, then the parts). In low light but not nightime, 1700 is a bright orange color, similar to how a sunrise looks when it's all the way up. The darker the ambient light, the brighter 1700 degrees will look. 2 hours at 1700 degrees should yield around 10 thousandths of surface hardening, which is very close to how these parts are leaving the factory. You maintain that heat by blowing air in from the bottom just like in a blacksmith's forge. You also need to have a small pile of charcoal getting ready to use when you start. Do not add fresh charcoal to the fire. It will suck the heat right out of it and delay the process. Get coals ready to use then drop them in as the fire burns down. Also be very gentle with the can once it's hot. At 1700 degrees, it is as fragile as tissue paper and if you move it around much as you add charcoal it will tear open.
I did the heat, and because of letting the fire burn down too much at one point it took 3 hours total to get the whole 2 hour soak done at heat. I then dumped the whole works out on the grill, and tore the can open and dumped it out in my wife's colander (she wasn't home!). I found that I had damaged the can during the heat by moving it, but I went ahead and seperated everything out and found the hammer and trigger and dropped them straight into my quenching water. I then did a 350 draw in the oven for an hour.
I had to do some very basic polishing to the parts after the process, and then I coated them with CLP since the original phosphate coating was long gone. I've done 100 dry fires so far with no change in the trigger feel. It's a smooth 4 pounds now and perfectly acceptable for my uses. I could get it lower with a reduced hammer spring or with one of the adjusters to remove sear engagement, but it's good enough for me now.
I'd love to hear from anyone else who does this. I can't say it was worth it just from a financial standpoint, because I could have bought the Bushmaster match trigger (trigger only) for about $40 and accomplished the same thing. But it was a fun experiment to do and I have kept all of the stock sear engagement so safety isn't a worry.
