It's totally worth it! I use 2-liter soda bottles or similar since diff soda bottles have diff thicknesses. It won't leave any plastic debris as long you do it correctly. An alum can is a bad idea imo, I can't imagine the alum working very well or it surviving, which one member here confirmed with bits of alum everywhere. You can also use spring tar which works very well, but very messy and costs you power which may fluctuate as it moves around. If you get some I'd get the black, not the clear. I had assumed I sent you my guide with the following in it but hard to keep track. So this is from my tuning guide and the pix shows a generic B18 Crosman, and the last pix is a Diana.
Piston liner / spring sheath : If you have a coil spring gun then I recommend something to dampen the annoying twang when the gun is fired. One way is to make a plastic liner that fits inside the piston so the spring isn’t as loose a fit and to eliminate metal to metal contact. Most importantly is it greatly reduces the annoying spring twang when fired, but also eliminates the klink klink klink sound when cocking and any other metal to metal sounds like scraping and groaning. It also reduces friction and wear, and keeps the spring straighter when cocked. It should make more power too but probably not much. The main point here is to reduce noise and increase smoothness. Cut out a section of a 2-liter bottle to match your piston. For a standard Crosman I’d cut out a piece about 2.6" x 5.7" with the curve matching the picture. You should sand the inside of the piston first to remove any high spots, roughness, or edges left from the stamping process. Those imperfections will make inserting the tight liner difficult and high spots will come thru and reduce smoothness when fired. I deburr the cocking slot first, then use sandpaper (320) on a stick (see pix) driven by a Dremel to smooth the pistons ID. You also want the inside edge of the cocking slot to be smooth and straight to minimize wear on the cocking shoe and help overall smoothness, so do that now before the liner is in. I also sand the outside of the spring with 600 paper which reduces friction and wear against the plastic since the oem spring can be a bit rough. I also sand both sides of the plastic. The piston side so it can better stick to the sanded ID of the piston to help prevent any shifting once installed, and the spring side so it can hold lube. I usually use 320 to sand each side. I sand by hand just enough to break all the shine leaving a matte finish. Making the liner the perfect width to tightly fit the piston can be a pita and you may screw up a few times before getting it right, so with that in mind you might consider sanding the plastic after you get the fit good because the plastic is tough and sanding takes some time and effort. The finished size of the piece pictured was 2.4" wide (I think), but the pistons ID and even length can vary. For example the next one I did was 2.5” wide which is quite a difference. Many Canadian pistons can also be much longer so adjust accordingly. Basically just measure the ID of the piston and x by pi (3.14 outta do it), then maybe add a bit to be sure. You can also make a thin strip of say 1/2" wide and cut until a nice tight fit, then you have a much better idea, which is especially handy if you don't have a good tool for measuring the ID. Once the width of the plastic is perfect for a tight fit, and by that I mean you work it into the piston with the ends butted together and it's a tight fit all the way down. Ideally so tight you can barely get it all the way in. Keep your mind out of the gutter... This is ideal but not required, a looser fit should still work but the liner won't be perfectly round in there and the looser it is the more likely it may move around or the ends become unbutted. I've never made one that loose so I can't say what will happen, but I suppose worst case is it'll come out and get tore up and jammed in the gun, so annoying but nothing serious. A typical 2-liter bottle is ~.012-.015", even .018 thick, but usually that's not enough to make the spring a tight fit in the piston, but it does work wonders in noise reduction. A typical Crosman spring is ~ .730" OD and the piston ~.790", which means a liner of .015" plastic will only reduce the space between spring and piston by half, so if you want a tighter fit you have room to do it. You could make a sheath from thicker plastic, or make a second sheath to fit inside the first one. If you have a Canadian spring that has a smaller OD then your gap between the spring and piston will be even greater. Other kinds of bottles like Vinegar or smaller soda/flavored water bottles may have thicker plastic. Look in the grocery store for options. Plastic from packaging will work too if you can find a section large enough to use. Also note that the spring should expand a wee bit when compressed, but it's not much and shouldn't be enough to cause problems. I'd be surprised if the OD expands more than .010", so I'd only be concerned if the relaxed spring is a snug fit. Once your plastic piece is sized to fit perfectly in the piston, you need to make the teeth end shown in the pix. Bend one end about 8 to 10mm back to make a 90 degree angle, then cut notches in it like the picture to make teeth. It's ok to have gaps or be uneven, you just don't want any teeth to overlap when it's rolled up in the piston. With this end being held under the pressure of the spring, and the liner being a tight fit, hopefully it'll never move. Optionally you could put a dab of super glue or epoxy between the piston and plastic at the skirt end so the liner can't rotate. Just wedge a toothpick or whatever between them to get in there. If the liner is not tight it'll likely rotate, and my version of tight is likely different than yours so it's hard to say how tight is tight enough. All I can really say is when I install the liner it's pretty friggin tight, like any tighter and the plastic may buckle rather than go it. Combined with both surfaces being sanded I think it's locked in. Maybe if grease works it's way in there maybe it'll move but I don't use that much grease so I guess I'll never know. You'll probably need to grind/sand down the OD of the spring hat to fit inside the liner. I had to take about .010" off the OD for one liner of 2-liter bottle, plus bevel the edges and it fit perfectly. Thicker or two layers you'd need to grind more. You don't want the hat to be so tight you can't get it back out, but you don't want it very loose either. Mine is tight enough that I need to hit the piston against my hand a few times to get it out. With the plastic sheath in place, put a little grease on the edge of the spring hat and force it down in there as tight as you can using the spring or a dowel etc. The idea is to forcibly shape the end of the plastic to match the piston and hat. Kinda sorta, but once put together it'll do that on its own. Note that extra plastic will shorten the overall compressed height of the spring, which should not cause any issues unless you had planned on using shims or increased the guns stroke. But if it's a problem you'll find out when you try to cock it. Now you should have some excess plastic extending out the skirt end of the piston. You don't want the spring to catch the plastic when cocking so you have two options; one is cut it off flush with the end of the piston and bevel the inside edge, or leave 1-2 mm sticking out and flare it a bit. If you leave some out be sure it doesn't hit when cocked because some guns the piston skirt hits the trigger assy or whatever is back there when cocking. So being plastic should eliminate the clink clink sound of coils when cocking, but beveling/flaring will make certain of it and should eliminate any feeling of them catching. The liner should be a fairly tight fit and shouldn't move once installed, but keep an eye on it while trimming and beveling. I like to dry lube the inside of the liner, then grease it, or you can simply grease it. Install the sheath before greasing it because it's much easier to work with dry. Do not grease the inside of the piston or the outside of the sheath, you don’t want it slick there and causing the sheath to shift during use. You may want to coat the inside of the piston with something to prevent rust, preferably something light meant for protection, not something slick. I use penetrating oil similar to WD-40 that protects but isn’t slick. I live where it's pretty dry and have virtually no rust issues anyway so I guess use good judgment. While this liner reduces spring twang quite a bit, it typically won’t do it as well as spring tar, but tar is horribly messy, reduces power, and costs about $8 + shipping. It all depends on the sheath and guide tightness vs qty of tar, but while the sheath does an outstanding job on the piston end, it does little to nothing on the guide. Tar will do an excellent job on the guide. If done well I think the sheath can be as quiet as tar but each gun and work done is different. If you’re looking to be as quiet as possible you can always do this mod and put a little tar on the guide. I’ve never tried tar with this mod, no need, but it will certainly quiet any remaining guide noise. How much power you will lose by adding tar I can’t say because it is again dependent on the gun and how much you use, but with the sheath and guide dry lubed and greased I suppose you wouldn't lose much.
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