AG1212 Posted June 26, 2011 Report Share Posted June 26, 2011 The set up of my new project gun will allow me to swap between a 20~ inch (509mm) and 8.5 inch (???) barrel with ease, but this creates a problem in terms of cylinder volume. As I understand it if you have too little a volume of air you will suffer from poor FPS or ''suck-back'' (if that even exists), and if you have too much it may cause extra strain? are both true/untrue or just the one? So in short what cylinder should I use when switching from a 20~ inch barrel to an 8.5 inch barrel? Thanks! Link to post Share on other sites
Krut Posted June 26, 2011 Report Share Posted June 26, 2011 8.5 inches is equal to 215.9 millimeters. Some people say that a type 0 cylinder works fine in all guns, and others say it doesn't. However, if you use a 509mm barrel, you need a type 0 cylinder. Conventional thinking would tell you would need a type 2 cylinder for the 215.9mm barrel. Link to post Share on other sites
Krut Posted June 26, 2011 Report Share Posted June 26, 2011 But in my opinion, it would be better to use a type 0 for both, than a type 2 for both Link to post Share on other sites
RSM Posted June 26, 2011 Report Share Posted June 26, 2011 A no hole cylinder will probably work best as stated, with the shorter barrel all the excess air volume from the cylinder will just go into the air on leaving the muzzle, I think the gun may sound louder but you will also lose some power...G&P do this on their stubby killers as a lot of people reported a jump in FPS when installing longer barrels so you'll want to factor that into your build. Link to post Share on other sites
AG1212 Posted June 26, 2011 Author Report Share Posted June 26, 2011 Cooleo, The FPS drop shouldn't be a problem as the 8.5 inch is obviously going to be for CQB, thanks! Link to post Share on other sites
Docv400 Posted June 26, 2011 Report Share Posted June 26, 2011 ... if you use a 509mm barrel, you need a type 0 cylinder... Don't agree My Son's JG AUG A3 has a 509mm inner, and uses a ported cylinder. It was firing at 420 when we got it, and to get it to 350 I had to cut the spring down until it fitted into the box with no virtually no preload at all. There was a discussion here a while back questioning the conventional cylinder-to-barrel matching idea. Link to post Share on other sites
ctres94 Posted June 27, 2011 Report Share Posted June 27, 2011 Yup, I am pretty sure that nearly every stock tm designed/cloned aeg has too much cylinder volume, probably to compensate for poor compression, or maybe just miscalculation during design, idk. As Docv400 said, you don't necessarily need a 509 mm barrel, you actually may gain a higher fps efficiency with a ported cylinder, however, you would probably want to perfect compression as much as possible beforehand. I think the main thing to remember here is that you probably don't want a lack of volume. You will be better off with a cylinder suited for a 509mm barrel (whatever type of cylinder it is that you find best) than one with the correct volume for a really short barrel. Link to post Share on other sites
Krut Posted June 27, 2011 Report Share Posted June 27, 2011 Yeah I agree with that, use the better suited cylinder for the longer barrel Link to post Share on other sites
Alaskanairsofter Posted June 27, 2011 Report Share Posted June 27, 2011 Food for thought volume of a cylinder=3.142 x r 2 x H volume of a full type cylinder (h=72mm )= 35347.5mm3 volume of a ported type cylinder (H=42mm)= 20619mm3 volume of a inner berrel length 509mm and with of 6mm =14393mm3 Also the closer the volumes of the barrel and the cylinder are the quieter the pop at the end of the barrel will be. Link to post Share on other sites
AG1212 Posted June 27, 2011 Author Report Share Posted June 27, 2011 Food for thought volume of a cylinder=3.142 x r 2 x H volume of a full type cylinder (h=72mm )= 35347.5mm3 volume of a ported type cylinder (H=42mm)= 20619mm3 volume of a inner berrel length 509mm and with of 6mm =14393mm3 Also the closer the volumes of the barrel and the cylinder are the quieter the pop at the end of the barrel will be. Now I'm just confused, when it comes to airsoft there seems to be a lot of conventional science behind various things, then someone comes a long and disproves everything.... Are you saying that if I had perfect compression I should actually be using a ported cylinder? also I was wondering mainly about whether having too high a cylinder volume (relative to the barrel) would it cause any additional wear the the piston head or something? Link to post Share on other sites
Docv400 Posted June 27, 2011 Report Share Posted June 27, 2011 I don't think you can apply simple calculations to this, as there are too many variables to take into account. Air, as we all know, is compressible, it also changes density with temperature, a particular day's atmospheric pressure, and altitude. Add to that the many different permutations of parts you can use in an AEG that affect the air pressure produced (and how efficiently that pressure is utilised), and the frequency and amount of maintenance it gets (or more importantly doesn't), and I'd say the best you can hope for is to use the volume idea as a basic guide. Then you have the age-old question of . . . "at what point does the BB start to move...?" to throw into the mix. As I'm sure we've all experienced at some time, you often get AEGs which perform well above, or below, the expected, for no apparent reason. You only have to look through some of the topics on here to see that Link to post Share on other sites
Alaskanairsofter Posted June 27, 2011 Report Share Posted June 27, 2011 Now I'm just confused, when it comes to airsoft there seems to be a lot of conventional science behind various things, then someone comes a long and disproves everything.... Are you saying that if I had perfect compression I should actually be using a ported cylinder? also I was wondering mainly about whether having too high a cylinder volume (relative to the barrel) would it cause any additional wear the the piston head or something? I see no reason for it to cause extra wear on any thing I have a full cylinder in just about every gun I own some have been in use for afew years with no extra wear noticed. and yes a ported cylinder will work just fine with a long barrel but if you are trying to get a major fps jump in the system a full cylinder helps alot. but if you are not making a dmr a ported cylinder is all that is needed. I know of and have built/worked on some super high fps set ups that have the stock ported cylinders and would probably expect a 20 to 60 fps gain in them from installing a full cylinder if you still dont under stand think of this there is a small kid on a seesaw in a park and two different guys ready to jump on the other end to in effect launch the kid in the air one of them is really skinny and the other kinda heavy which one do you think will make the kid fly further . now if you think of the difference in weight between the two guys as the difference in volume between a ported and full cylinder. and if you use the same spring you can refer to gravity as the spring in this scenario. Link to post Share on other sites
AG1212 Posted June 27, 2011 Author Report Share Posted June 27, 2011 Hmm, it's starting to become a bit clearer. My setup will be using a guarder SP85 spring, which is rated (from what I have seen) anywhere from 270-310 FPS, so with good compression/air seal and a full cylinder I should be getting as close to 328 FPS without worrying about going over with changing atmospheric conditions? Link to post Share on other sites
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