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Posted: 12/24/2015 11:26:02 AM EDT
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As a datapoint, I have began using a QPQ'ed BCG, and the cam-pin is also QPQ'ed.
Here are pictures of it at about the 500 round mark, mostly suppressed: 
Here are pictures of it with another 2000ish rounds on it, almost 100% suppressed. 
Here is a Colt of mine with about 50-100 
Here is my DDM4 cam pin with around 1000 on it. 
Thus far, I am very pleased with how the QPQ'ed cam-pin resists deformation and grooving. |
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How do Hard Chrome cam pins hold up? The same as phosphate, in my experience, regarding "grooving", and better, regarding "shiny spots". The metal under the chrome is no harder, and it "grooves" in the half-moon shapes as seen on the Phosphate cam-pin just the same. I tried HC BCG's because I thought they would be better, and was not very impressed. |
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What is QPQ ??? Quoted:
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As a datapoint, I have began using a QPQ'ed BCG, and the cam-pin is also QPQ'ed. Thus far, I am very pleased with how the QPQ'ed cam-pin resists deformation and grooving. What is QPQ ??? One of the versions of Melonite, QPQ stands for Quench, Polish, Quench. |
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Tell me why these findings are anything other than cosmetic? My phosphate DD and LMT BCGs continue to chug along without cleaning or problems. The more wear the cam pin experiences, the more slop the fit in the bolt has, the more shock loading occurs during cycling. The cam pin hole is one of the common failure points on the m4 bolt. |
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The more wear the cam pin experiences, the more slop the fit in the bolt has, the more shock loading occurs during cycling. The cam pin hole is one of the common failure points on the m4 bolt. Quoted:
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Tell me why these findings are anything other than cosmetic? My phosphate DD and LMT BCGs continue to chug along without cleaning or problems. The more wear the cam pin experiences, the more slop the fit in the bolt has, the more shock loading occurs during cycling. The cam pin hole is one of the common failure points on the m4 bolt. That makes no sense. The wear pattern occurs where the pin interfaces with the BCG, not the bolt. The cam pin hole is a common failure point because it has the least amount of metal of the surrounding area. |
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That makes no sense. The wear pattern occurs where the pin interfaces with the BCG, not the bolt. The cam pin hole is a common failure point because it has the least amount of metal of the surrounding area. Quoted:
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Tell me why these findings are anything other than cosmetic? My phosphate DD and LMT BCGs continue to chug along without cleaning or problems. The more wear the cam pin experiences, the more slop the fit in the bolt has, the more shock loading occurs during cycling. The cam pin hole is one of the common failure points on the m4 bolt. That makes no sense. The wear pattern occurs where the pin interfaces with the BCG, not the bolt. The cam pin hole is a common failure point because it has the least amount of metal of the surrounding area. It makes a lot of sense. When the cam pin wears where it rides against the carrier it has more room to slam around. That could transfer shock into the weak part of the bolt |
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It makes a lot of sense. When the cam pin wears where it rides against the carrier it has more room to slam around. That could transfer shock into the weak part of the bolt Quoted:
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Tell me why these findings are anything other than cosmetic? My phosphate DD and LMT BCGs continue to chug along without cleaning or problems. The more wear the cam pin experiences, the more slop the fit in the bolt has, the more shock loading occurs during cycling. The cam pin hole is one of the common failure points on the m4 bolt. That makes no sense. The wear pattern occurs where the pin interfaces with the BCG, not the bolt. The cam pin hole is a common failure point because it has the least amount of metal of the surrounding area. It makes a lot of sense. When the cam pin wears where it rides against the carrier it has more room to slam around. That could transfer shock into the weak part of the bolt That isn't what he stated, and that isn't what happens. It makes no sense. That wear spot doesn't cause anything to flop around because it doesn't start moving until it is fully loaded to one side. All the force is to one side when it is unlocking, and all the force is to the other side when it is locking. When the bolts break at that point, they have suffered brittle fracture, and is most likely caused by improper manufacture or fatigue caused by heat cycles. That section is more susceptible because of its reduced cross sectional area. |
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had one break on me years ago when i was into heavy full auto when 5.56 was about 10 cents/round. I change them out every 5 years or so now. The bolt or the cam pin? In either case, time is irrelevant to their failure. Why would you change them every 5 years? |
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The bolt or the cam pin? In either case, time is irrelevant to their failure. Why would you change them every 5 years? Quoted:
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had one break on me years ago when i was into heavy full auto when 5.56 was about 10 cents/round. I change them out every 5 years or so now. The bolt or the cam pin? In either case, time is irrelevant to their failure. Why would you change them every 5 years? cam pin broke. no need to change them every 5 or so years, I just feel better doing it since I had one break on me. probably not necessary. YMMV as they say |
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