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Posted: 7/17/2010 6:44:22 AM EDT
| I understand that you do not want to stone a trigger because you can remove the hard outer surface and then begin to shoot doubles. Has anyone tried stoning and then heat treating the trigger afterword? |
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I'm still waiting to be convinced that there is a paper thin surface hardening in trigger groups. If so, how do the manufacturers get around it? Heat treat the parts AFTER cutting the sear notches? If that's the case, why are the cuts shiny while the rest of the metal is black?
I think that the metal is heat treated to a certain hardness level prior to being cut, and that there is no "surface" hardening, but rather a level of hardness in the entire piece. If stoning metal will get into a soft gooey center, I'd better stop sharpening my knives, and thousands of gunsmiths over the past century have been idiots! How do they explain the tens of thousands of successeful gunsmith trigger jobs? Only AR triggers are made with a soft gooey center? Does that make any sense? I work all my triggers, gently stoning out any machining marks and polishing them to a mirror shine. This and a good set of springs and quality grease and I'm very happy with a factory trigger group. 
Link to a threadwith a couple pages of discussion on it.... |
| I haven't seen anything verifying that they are only surface hardened either. But the quality of metal that these standard triggers are made from is no where near a nice knife steel. Also if you sharpen your knife very much you will see that the blade will eventually get smaller, because you are removing material. You don't have much wiggle room on the trigger to remove material before things go wrong. With all the reports of rifles going double or worse I didn't want to chance it, so I took some mothers mag polish and put a dab on the trigger where the sear meets. Then dry fired it a bunch letting the hammer down easy. Then disassembled the FCG and cleaned real well. Visibly you can't hardly see a difference on the surface, but it got rid of the terrible gritty feel on my LR-308. Then I gave it the grip scew mod, and slight bend in the trigger springs with some round spinnerbait pliers. The overall difference was amazing, have yet to shoot it though. That being said I'm still going to get a Timney when I have the funds. |
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You are thinking about two VERY separate processes when comparing a knife to gun parts. When making a knife you use a process called tempering that makes a homogeneous hardness through the entire blade. This puts the steel into a mid-grade hardness level so it is both flexible and strong. You heat it to a high temp and quench it so that carbon atoms are trapped in the steel. Then you heat it to a middle temperature and allow it to cool in air. This is where the word "tempering" comes from.
When talking about stress gun parts like hammers, triggers and bolts, you use a completely different process because the stresses on a rifle bolt are completely different from a knife. It is a process called case hardening. You harden the entire part to a mid-grade hardness to make the metal resilient to beating. It is flexible, but not particularly resistant to metal on metal wear. If you stop here, you have a part that will prematurely wear, much like the Chinese M14 bolts in the link below. To stop this, the part is then treated with a surface hardener that prevents metal to metal wear. So if you grind too hard on an AR trigger, you are removing this surface hardening, increasing wear of the part over time. Metallurgy of a gun in a nutshell You'll notice in that thread that the core metal of the bolt is several points lower on the Rockwell scale than the surface. But in all the bolts, the surface hardness falls below the recomended GI spec of 50-60 Rockwell and show wear that could make the rifle unsafe to fire if not watched (much like the AR trigger that is improperly stoned). The problem isn't "AR triggers with a gooey center." Its the fact that most people don't know how much stone to use when working a trigger and end up with crap. It is possible to stone the trigger without removing all of the case hardening, but it takes a pro's hand at it. |
| I wiped my trigger on 1000grt wet sandpaper and bent the hammer spring as seen done in numerous pictures on the internet and I'm perfectly fine with my trigger. I planned to replace it with a quality aftermarket if/when it shows signs of problems but it's still looking good. I only polished it in the direction it would work against the hammer and I didn't take it down to where 100% of the machine marks were gone either. I'm sure it's okay. |
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Obviously(or apparently not) I don't think that FCG's have a "gooey center", my point was that you can carefully stone the machining marks out and polish the metal without "ruining it". I do not and have not advocated making radical changes in the sear.
I'm still waiting for someone to explain these two issues: If the FCG is case hardened and cutting it will penetrate; why is the part black or gray and the cuts for the sear surfaces shiny and bright? It apears to me that every one I have ever looked at machining the cuts was the final operation AFTER whatever heat treating process was done was completed. HOW does this not "PENETRATE" the surface hardening, yet somehow stoning will? Issue two; if stoning triggers is bad, why have gunsmiths been doing it for the last century? |
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Quoted:
Obviously(or apparently not) I don't think that FCG's have a "gooey center", my point was that you can carefully stone the machining marks out and polish the metal without "ruining it". I do not and have not advocated making radical changes in the sear. I'm still waiting for someone to explain these two issues: If the FCG is case hardened and cutting it will penetrate; why is the part black or gray and the cuts for the sear surfaces shiny and bright? It apears to me that every one I have ever looked at machining the cuts was the final operation AFTER whatever heat treating process was done was completed. HOW does this not "PENETRATE" the surface hardening, yet somehow stoning will? Issue two; if stoning triggers is bad, why have gunsmiths been doing it for the last century? I found many testimonials that state that increased wear occurred after stoning an AR trigger. Both home jobs AND gunsmiths. "I tried one similar to that which I found off a internet site and it did not take long til my trigger started to not catch. Got a few double taps. At first I could not figure out what was wrong, then it dawned on me it must have been my do it yourself trigger job. I took to much of the surface off and got through the hardener and just kind of rounded my parts off a little. It only took 300 to 400 rounds to cause it. But it was fun having it burst on the range. Big Smile It was most likely me just not doing it right, but it made me pretty nervous about doing it again. I replaced it with a Timney and it is much better than my trigger job anyway. Course it cost me $200 Brownells sell surface hardener that you can apply with a torch to harden it back up. Might be worth doing. A couple guys I know have used it on AR parts and said it works great. " From at least 10 people I can find just with Google, you don't have to make any severe changes to the sear angle. Stoning the trigger WILL lead to advanced wear once the hard layer is gone. As far as the production methods, I have no idea. There should be spec sheets floating around the internet that tell you exactly what is required. The best I can figure is the part is machined, hardened, parkerized, and some wire brush (softer than steel) is used to remove the parkerizing on selected surfaces. By using a bronze wheel, you can remove the park without fear of compromising the case hard layer. OP, there are several compounds available from Brownells that are used to harden low carbon steels. One is known as Kasenit and is pretty commonly used. It is possible to re-harden the surface after stoning, but unless you have experience hardening metals, its not recommended. |
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Quoted:
Why would tempering the whole trigger not be advised? Because tempering still raises the Rockwell on the part, making it prone to breakage. When hardened, steel can become brittle and break under the stresses you find in triggers under recoil. There have actually been several sets of early Arsenal brand US trigger groups that were too hard and fractured during firing over on the AK side. Case hardening is more like Japanese blades. The spine of the blade is like the soft core of the hammer. It provides a flexible backbone to prevent breakage, but at a much lower hardness that would otherwise wear prematurely. The edge of the blade is hardened like the outer layer of the hammer to reduce wear from abrasion. The two techniques together allow the part to be both tough and flexible and survive the relatively violent action of a firearm. It may also have to do with trigger groups being cast too. Certain steel alloys can't be hardened in the same way others can. |
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