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Posted: 6/21/2009 4:45:01 AM EDT
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Alrighty,
So I'm thinking of picking one of these up. Is there any reason to avoid a SS LPK? Metallurgy OK? etc. |
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R-Guns makes them, is what Brian at AIM said. |
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Recently in my materials engineering course we did some hardness testing of different types of steels with a Rockwell hardness tester. The stainless was about 8-15% less hard than the carbon steels (1018, 1045, hot and cold rolled, etc).
It also pulled apart easier in a tension tester. Not that this is anything new, but it was cool to actually see the difference in real testing. ETA: I believe the stainless was 304. ETA2: go with the standard LPK, imo. |
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Recently in my materials engineering course we did some hardness testing of different types of steels with a Rockwell hardness tester. The stainless was about 8-15% less hard than the carbon steels (1018, 1045, hot and cold rolled, etc). It also pulled apart easier in a tension tester. Not that this is anything new, but it was cool to actually see the difference in real testing. ETA: I believe the stainless was 304. ETA2: go with the standard LPK, imo. As SS is softer than carbon steel, it is more elastic, meaning it can "flex" and return to its original state better than carbon steel (in other words, it's less brittle). Is there any advantage to this in a LPK? |
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Recently in my materials engineering course we did some hardness testing of different types of steels with a Rockwell hardness tester. The stainless was about 8-15% less hard than the carbon steels (1018, 1045, hot and cold rolled, etc). It also pulled apart easier in a tension tester. Not that this is anything new, but it was cool to actually see the difference in real testing. ETA: I believe the stainless was 304. ETA2: go with the standard LPK, imo. As SS is softer than carbon steel, it is more elastic, meaning it can "flex" and return to its original state better than carbon steel (in other words, it's less brittle). Is there any advantage to this in a LPK? I doubt it. I have never heard of anyone having issues with their standard LPKs being brittle or having fracturing or anything like that. I don't see how a softer metal would give any advantage. If anything the stainless is probably more likely to deform over time. The stainless was cool to watch get pulled apart. It definitely was more elastic before it started necking. It elongated more than the other steels as well. Had a more "silly putty" look to it (when under 15kN force anyway) than the other metals tested. |
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Recently in my materials engineering course we did some hardness testing of different types of steels with a Rockwell hardness tester. The stainless was about 8-15% less hard than the carbon steels (1018, 1045, hot and cold rolled, etc). It also pulled apart easier in a tension tester. Not that this is anything new, but it was cool to actually see the difference in real testing. ETA: I believe the stainless was 304. ETA2: go with the standard LPK, imo. As SS is softer than carbon steel, it is more elastic, meaning it can "flex" and return to its original state better than carbon steel (in other words, it's less brittle). Is there any advantage to this in a LPK? I doubt it. I have never heard of anyone having issues with their standard LPKs being brittle or having fracturing or anything like that. I don't see how a softer metal would give any advantage. If anything the stainless is probably more likely to deform over time. The stainless was cool to watch get pulled apart. It definitely was more elastic before it started necking. It elongated more than the other steels as well. Had a more "silly putty" look to it (when under 15kN force anyway) than the other metals tested. I too performed that test in my materials engineering class at VA Tech. Was pretty cool. ETA: in the test, do you remember at what stress the stainless steel yielded at versus the carbon steel? I wonder what stresses these lower parts ever actually see? I still think there could be an advantage to SS parts, but like I said, it all depends on what stresses and strains they are subjected to. Anybody know what grade (strength) carbon steel is typically used for lower parts? |
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Almost all stainless steel used in firearms is ferrous (check w/ magnet) and will therefore also rust. We made some gearboxes out of SS for a marine application (mini subs) and that stuff was very hard to machine, usually SS cuts like butta'.... but not that stuff. I dont recall the grade as it was 15+ years ago.... but they held up nicely and we had a few more small orders for spares, quicker to swap out a complete unit vs repairs.
For the $$, I would stick w/ standard LPKs..... |
| not sure what kind of stainless steels you guys worked with, but in general most stainless steels are a bitch to machine compared to regular cold rolled steel. When you start working with the duplex stainless steels like 2507 or even the nitronic stainless steels stand the fuck by and prepare for work hardened hell. |
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Recently in my materials engineering course we did some hardness testing of different types of steels with a Rockwell hardness tester. The stainless was about 8-15% less hard than the carbon steels (1018, 1045, hot and cold rolled, etc). It also pulled apart easier in a tension tester. Not that this is anything new, but it was cool to actually see the difference in real testing. ETA: I believe the stainless was 304. ETA2: go with the standard LPK, imo. As SS is softer than carbon steel, it is more elastic, meaning it can "flex" and return to its original state better than carbon steel (in other words, it's less brittle). Is there any advantage to this in a LPK? Not necessarily true. That's not an apples-to-apples comparison. You could compare the same "grade" (chemical composition) of carbon steels heat treated to different hardnesses that way, but you can't compare a stainless steel to a carbon steel in the same fashion. There are far too many factors to take into consideration. Not that you'd want your LPK flexing anyway. 
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Think it would depend on the type SS. I've used Carpenter Custom 475 on some pretty demanding orthopedic devices with good luck:
http://cartech.ides.com/datasheet.aspx?&I=101&E=326 Wonder if R-guns would tell us what type of SS they use in their LPK. |
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not hard enough, wont hold up. I figured it was a gimmick to get unsuspecting buyers to purchase a substadard product.It would look good on some guns.I would'nt want it on any of mine.I thought if it's so good why are they waiting till now to come up with it. |
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not hard enough, wont hold up. I figured it was a gimmick to get unsuspecting buyers to purchase a substadard product.It would look good on some guns.I would'nt want it on any of mine.I thought if it's so good why are they waiting till now to come up with it. Because it's not mil-spec. 
SS has been used in firearms applications for a long time. Long enough to know what works or doesn't. If these parts are manufactured using that experience then I'd be willing to bet they are GTG. |
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Quoted: Quoted: Quoted: not hard enough, wont hold up. I figured it was a gimmick to get unsuspecting buyers to purchase a substadard product.It would look good on some guns.I would'nt want it on any of mine.I thought if it's so good why are they waiting till now to come up with it. Because it's not mil-spec. SS has been used in firearms applications for a long time. Long enough to know what works or doesn't. If these parts are manufactured using that experience then I'd be willing to bet they are GTG. GTG? Would you trust this kit in your weapon system if you just paid $500 for a tactical carbine course and were counting on this LPK to perform? |
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not hard enough, wont hold up. I figured it was a gimmick to get unsuspecting buyers to purchase a substadard product.It would look good on some guns.I would'nt want it on any of mine.I thought if it's so good why are they waiting till now to come up with it. Because it's not mil-spec.
SS has been used in firearms applications for a long time. Long enough to know what works or doesn't. If these parts are manufactured using that experience then I'd be willing to bet they are GTG. GTG? Would you trust this kit in your weapon system if you just paid $500 for a tactical carbine course and were counting on this LPK to perform? It was an If/Then statement. Running them hard would be the only way to find out for sure about reliability. I would certainly have a spare along anyway even if my main gun was from a kool-aid maker.
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The material in Rguns LPK is not going to Gal, its not pure SS and is just as hard as any other LPK I would bet. You're basing this statement on what info other than the magnetic properties someone else here observed? I've used stainless that was noticeably magnetic in some marine equipment that wasn't necessarily so because it was a nifty alloy, it was just shitty quality. |
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not hard enough, wont hold up. This LPK or one made of SS in general? I wonder, trigger/ hammer components for firearms have been made from SS for a long time, have never heard of any wearing out before a non SS part. I would not think an AR lpk is under any more stress than say a hammer/ sear in a SS 1911. |
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Depends entirely on what grade and how it was worked. You can get SS to be just as hard as most firearm grade carbon steel, but you tend to have 20% more cost in material and about 50% cost increase in the mfg process of the part. yup. incidentally, 304 was an interesting choice for the instron tests in class, about 73ksi FTU and a Vickers Hardness of 129 check out something like 17-4PH, cond H1150 stainless with 144ksi FTU and a Vickers Hardness of 325 for comparison, 4140 Oil quenched is 140ksi FTU with a Vickers hardness of 301 I'm not a materials guy but I know when I'm looking for something with strength at work, 300 series doesn't enter the equation since it just doesn't cut it. at my last place with valves and manifolds, yeah, lotsa 300 series stuff especially in medical stuff. As NVBGear said, the stainless stuff is usually more per pound. For quick example, looking at one source online, uncertified, annealed 17-4 stainless, 2in bar is $77 per foot. annealed 4140 the same size is $36 per foot. assuming the heat treat process was the same, it's still almost 2X the material cost. yeah, i know, 4000 series steel will rust and 17-4 needs to be passivated etc, but just trying to shed some light in a very short space on likely why more parts aren't high end stainless. and like the machinist from earlier said, some of the stainless is a bitch to machine, some of it is gummy, some stringy, etc. For what it's worth, i use as much stainless as i can when designing things for its corrosion resistance and amenability to welding, but yes, need to be wary of galling issues. |
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