AegisDei 2 Posted October 31, 2006 Report Share Posted October 31, 2006 Tony is awesome enough to help me out in my forever-ongoing project to combine physics with guns by hookin' me up with an aluminum piston. So the question is...what will happen? Aluminum has a density of ~0.1lb/cu-ft vs. steel's ~0.3lb/cu-ft, but on average is about 1/2 as hard. Will it get all bent out of shape and fail miserably? Or will it let me reduce the weight of the piston thereby improving cycling-rate and reliability? Exciting times! I love science projects... Quote Link to post Share on other sites
rebelyell76t 0 Posted October 31, 2006 Report Share Posted October 31, 2006 Tony is awesome enough to help me out in my forever-ongoing project to combine physics with guns by hookin' me up with an aluminum piston. So the question is...what will happen? Aluminum has a density of ~0.1lb/cu-ft vs. steel's ~0.3lb/cu-ft, but on average is about 1/2 as hard. Will it get all bent out of shape and fail miserably? Or will it let me reduce the weight of the piston thereby improving cycling-rate and reliability? Exciting times! I love science projects... Depends on what grade aluminum you use for it. I would probably start with at least T6061. It's a bit harder than 3000 series aluminum. You might even think about getting it hard annodized which means that it will have to be machined just a touch under size. This should help to reduce wear. Quote Link to post Share on other sites
gunboy69 50 Posted October 31, 2006 Report Share Posted October 31, 2006 Tony is awesome enough to help me out in my forever-ongoing project to combine physics with guns by hookin' me up with an aluminum piston. So the question is...what will happen? Aluminum has a density of ~0.1lb/cu-ft vs. steel's ~0.3lb/cu-ft, but on average is about 1/2 as hard. Will it get all bent out of shape and fail miserably? Or will it let me reduce the weight of the piston thereby improving cycling-rate and reliability? Exciting times! I love science projects... Very cool project! I assume if it works, Tony will have even less time to himself. Quote Link to post Share on other sites
AegisDei 2 Posted November 1, 2006 Author Report Share Posted November 1, 2006 Depends on what grade aluminum you use for it. I would probably start with at least T6061. It's a bit harder than 3000 series aluminum. You might even think about getting it hard annodized which means that it will have to be machined just a touch under size. This should help to reduce wear. The tolerances for a piston are within 0.002". Is it even possible to hard annodize to that strict a tolerance? And how much weight would it add? The mass savings are so slight as is, I hate to do much to increase them. I was thinking about titanium instead, but since this is still in experimental stages I can't justify that kind of money. Maybe if the aluminium proves to improve cycling but lacks hardness, but for now we'll see what happens with the aluminium. Quote Link to post Share on other sites
BattleRifleG3 16 Posted November 1, 2006 Report Share Posted November 1, 2006 If anything should be made from titanium it would be a piston - A surface much easier to grind. About piston tolerances - since when was a gas piston supposed to be within 0.002"? What on earth does it fit inside that requires that sort of tolerance - certainly not the gas tube? Quote Link to post Share on other sites
AegisDei 2 Posted November 1, 2006 Author Report Share Posted November 1, 2006 If anything should be made from titanium it would be a piston - A surface much easier to grind. About piston tolerances - since when was a gas piston supposed to be within 0.002"? What on earth does it fit inside that requires that sort of tolerance - certainly not the gas tube? That's word on the street...maybe I added an extra "0." Perhaps it's 0.02"? Maybe if the aluminium is noticably better than steel I'll up the anti and go with Ti. I thought it was a PITA to lathe though. Quote Link to post Share on other sites
BattleRifleG3 16 Posted November 1, 2006 Report Share Posted November 1, 2006 Hence the grinding. That's the way to get good tolerances on Titanium. Use a grinder for the final surface. That's how Tapco finishes their stainless SKS pistons. Quote Link to post Share on other sites
AegisDei 2 Posted November 7, 2006 Author Report Share Posted November 7, 2006 Wow! Thanks Tony!!! I got the piston today and it's SIGNIFICANTLY lighter. I don't have a scale, but I would predict that it's ~1/2 the weight. Just holding each I can feel a difference. I can't wait to see it in action and see if it makes any difference. I'll not get to go shooting until December 22nd (not that I'm counting the days or anything), so I'll post a report then. Quote Link to post Share on other sites
IndyArms 10,186 Posted December 25, 2006 Report Share Posted December 25, 2006 DECEMBER 24'th.... WELL??!!?!?!?!?!? LOL Quote Link to post Share on other sites
AegisDei 2 Posted December 25, 2006 Author Report Share Posted December 25, 2006 DECEMBER 24'th....WELL??!!?!?!?!?!? LOL Actually...after some work my gun ran great for the first time ever!!!! I went through about 100rounds of ammo with a ton of problems (FTE, FTF, etc), so I started looking closely at what was going wrong. After every shot I dropped the magazine out and looked from above and below to see what the issue was. I noticed that the rounds were being chambered without the rims slipping into the bolt and thus they weren't being properly extracted. So I figured it might be the buffer messing with the travel of the bolt carrier and thus it wasn't properly racking the next shell. So I removed the buffer and tried again to no avail. So I worried that perhaps the bolt was coming back too quickly and too far (is that even possible?). Perhaps the bolt carrier was coming so far back that the next shell slipped into battery in front of the bolt (or so I imagined with my ever so finite wisdom of guns). So I swapped out the reduced tension recoil spring with 5 coils removed for the original factory spring. And guess what happened? BLAM BLAM BLAM BLAM BLAM BLAM BLAM BLAM BLAM BLAM BLAM as fast as I could pull the trigger. Usually it FTF or FTE once every 5 shots at a slow pace, and the ratio of FTE/FTF to success worsened as rate of fire increased. But this was 11 rounds rapid!!! Unfortunately, at this point the neighbors were pissed (I had also gone through about 100 rounds of .223 and about 100 rounds of .357) so it was time for me to quit. I'm not sure if it's possible, but I think the enlarged ports and reduced spring tension caused the bolt to come back too quickly and too far. So while I did not get to try the aluminum piston (yet) I now have a gun I trust again. I have to shoot it some more to be sure that wasn't a lucky fluke, but it really did feel as reliable as my old S12 for those 11 shots. Using an aluminum piston is a method to get the bolt to come back "better", which I'm not sure is now needed on my S20 since I think it might cycle reliably. But I'll still try it out as a learning experiment just to see what happens. The goal is to decrease reciprocating mass to negate the need to open the gas ports. If it works on my S20 without destroying the piston (aluminum is more brittle than steel) then I'll cut my S12 back to 18" and see if an aluminum piston can make her cycle without enlarging the gas ports: a $35 piston swap is easier than getting that darn gas tube off. So I'll swap pistons out next time I go shooting (within the next week or so) and post my observations. I'm sad I didn't get to do my learning experiment, but I'm stoked my S20 ran better than ever. Quote Link to post Share on other sites
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