greg Posted May 11, 2009 Report Share Posted May 11, 2009 So, as per the title, I was going to stick this in the VSR thread but then thought the principle could apply to other ba springers. I did a bit of thinking about the vsr cylinder the other day: Firstly, was I right in thinking it has enough volume to support a 6mm barrel approximately 850mm long? & we pair it with 303mm & 430mm barrels! If this is true, like aeg's we could port it to maximize efficiency,,,,,,,,,,,,,,,,,,,,,or,,,,,,,,,,,,,,,short stroke it. After all, this is a huge waist of energy: Pulling the bolt back 90mm. With a g-spec 303mm barrel it would possibly only have to be pulled 40mm. Any one tried or heard of this? Figured I'd ask before embarking on a wild goose chase. Greg. Link to post Share on other sites
MDK_Marshal Posted May 11, 2009 Report Share Posted May 11, 2009 There;'s a cylinder head that does this. Hang on an I'll find it... EDIT: http://www.redwolfairsoft.com/redwolf/airs...il?prodID=18234 There you go. Link to post Share on other sites
L4byr1nth Posted May 11, 2009 Report Share Posted May 11, 2009 I think this thing has another use. Could it be an easier way of fine-tuning the FPS of an upgraded rifle? I'm building a VSR at the moment... If you fully Laylax the thing, you either smack in a 150 spring, and teflon tape the HOP/whip it, and hope for 500 FPS, OR you go for a 170 spring, and try and chop it down to 500 FPS What if you just always used a 170, and instead of the Laylax Cylinder Head, throw one of these in? Ben. EDIT:: Imagine one with removable sections, to notch your FPS up and down as you needed? Link to post Share on other sites
Senor Bear Posted May 11, 2009 Report Share Posted May 11, 2009 Link to item on original PDI page I was considering this to drop my fps down on my 350 fps VSR. With the stock spring it does 352 fps which I don't quite feel comfortable with due to site limits (they trust me enough to use it there, it isn't like it is a massive way past the limit). If I put my sp100 back in this may allow me to stay just under 350. Link to post Share on other sites
banjo Posted May 11, 2009 Report Share Posted May 11, 2009 A bit to late for me as I did the whole barrel/cylinder volume balancing act aaaaaages ago, did all my guns in the same weekend , and didn't even know such a beast existed so in a similar vain if you fitted one of those cylinder heads wouldn't you then have to calculate cylinder volume and then match the barrel length to suit, for better or worse I suppose its a trade off if you fit one, you loose fps but gain a short cocking action, or do what I did and drill a load of holes in the cylinder and gain a couple of fps and a quieter muzzle report and put up with a long pull Link to post Share on other sites
thewallhitme Posted May 11, 2009 Report Share Posted May 11, 2009 ive nver thought, gee i wish this bolt pull could be shorter. guess its a problem for some Link to post Share on other sites
Stealthbomber Posted May 11, 2009 Report Share Posted May 11, 2009 Why oh why do people always seem to calculate the volume of the barrel and the volume of the cylinder but ALWAYS fail to consider how much air is bypassed as the BB is fired? As a rule you need around 1.5x the barrel volume in the cylinder. If you can be bothered, calculated the volume of a cylinder 5.91mm diamater. Now, calculate the volume of a cylinder 6.03mm diameter. Deduct one from the other and it'll show you the static bypass. Bear in mind, however, that the piston pushes the air through the barrel much faster than the BB ends up travelling. Put simply, if the bypass air is (for example) doing 500m/sec when the BB is doing 100m/sec then a static bypass of 5% can be multiplied by 5 and result in a 25% gross wastage of air. Hence the need for a cylinder with a considerably bigger volume than the barrel. How do you figure out how to accurately set up a gun to compensate for all this? I dunno. Let me know when you figure it out. Link to post Share on other sites
AnotherJesus Posted May 11, 2009 Report Share Posted May 11, 2009 That cylinder head would not act in a similar way to the port in an AEG cylinder. The port allows the piston to accelerate without any air cushion, so it's traveling with some momentum when it starts acting on the BB. So you don't loose much fps by having a short barrel. I tried porting my G-spec with a spare cylinder when I was starting out. I ended up shredding the o-ring due to a poorly rounded port. I gave up after that. Nothing to say it wouldn't work. On the short stroking front, I was considering getting one of those piston heads. It would allow you a lot of room for a very heavy taper. Link to post Share on other sites
greg Posted May 11, 2009 Author Report Share Posted May 11, 2009 Why oh why do people always seem to calculate the volume of the barrel and the volume of the cylinder but ALWAYS fail to consider how much air is bypassed as the BB is fired? As a rule you need around 1.5x the barrel volume in the cylinder. If you can be bothered, calculated the volume of a cylinder 5.91mm diamater. Now, calculate the volume of a cylinder 6.03mm diameter. Deduct one from the other and it'll show you the static bypass. Bear in mind, however, that the piston pushes the air through the barrel much faster than the BB ends up travelling. Put simply, if the bypass air is (for example) doing 500m/sec when the BB is doing 100m/sec then a static bypass of 5% can be multiplied by 5 and result in a 25% gross wastage of air. Hence the need for a cylinder with a considerably bigger volume than the barrel. How do you figure out how to accurately set up a gun to compensate for all this? I dunno. Let me know when you figure it out. Totally agree on all fronts. It's why I was seeking advice gained by previous experience. I'm glad to see (from the two examples given) that I'm not the only one to have considered this, at least there is some substance to it. I'm not out to specifically shorten the pull length, I'm just out to make the system as efficient as possible. Ie, no waste on either side of the equation. In the case of the two examples, I think they have made the cylinder head too long, hence the loss of power, they probably didn't consider the air waisted down the barrel. As already hinted, I have only done a simple mathematic comparison to get the relationship between cylinder & barrel, no calculator or paper, just the squared radius of each (100 & 9), & the bolt pull (90). Indicating approximately 900mm barrel length? I personally like trial & error but find that theory gives a good starting point. A 500mm barrel would need approximately 50mm of bolt pull. Plus your 25% wastage, 62mm? So, a 28mm plug????? Ish. Greg. Link to post Share on other sites
greg Posted May 11, 2009 Author Report Share Posted May 11, 2009 I tried porting my G-spec with a spare cylinder when I was starting out. I ended up shredding the o-ring due to a poorly rounded port. I gave up after that. Nothing to say it wouldn't work. Yes I can see that being a problem. PDI do a vented cylinder & use a series of 1mm(ish) holes on about the first 25mm of the cylinder. I guess they went for the small holes to avoid trapping & tearing the o-ring. Greg. Link to post Share on other sites
greg Posted May 11, 2009 Author Report Share Posted May 11, 2009 ive nver thought, gee i wish this bolt pull could be shorter. Me niehter. I thought, why am I pulling this back 90mm if I will get exactly the same effect pulling it 40, or so. Greg. Link to post Share on other sites
greg Posted May 11, 2009 Author Report Share Posted May 11, 2009 Double bouble. Greg. Link to post Share on other sites
thewallhitme Posted May 11, 2009 Report Share Posted May 11, 2009 im just saying, i dont see it as such a problem. if you wanted to be that efficient, then surely things like the weight of the rifle and ammo capacity would be places to start aswell. then youd end up with a .5kg rifle with 200round mag that you only hav to pull the bolt 40mm back. big deal... however, i shall leave this thread as i have nothing more to say on the subject. hope i didnt cause any harm Link to post Share on other sites
greg Posted May 11, 2009 Author Report Share Posted May 11, 2009 I think this thing has another use. Could it be an easier way of fine-tuning the FPS of an upgraded rifle? I'm building a VSR at the moment... If you fully Laylax the thing, you either smack in a 150 spring, and teflon tape the HOP/whip it, and hope for 500 FPS, OR you go for a 170 spring, and try and chop it down to 500 FPS What if you just always used a 170, and instead of the Laylax Cylinder Head, throw one of these in? Ben. EDIT:: Imagine one with removable sections, to notch your FPS up and down as you needed? Have faith, get it right & you may need one of these to get under 500 with a 150. Greg. Link to post Share on other sites
chownsy Posted May 11, 2009 Report Share Posted May 11, 2009 Yes I can see that being a problem. PDI do a vented cylinder & use a series of 1mm(ish) holes on about the first 25mm of the cylinder. I guess they went for the small holes to avoid trapping & tearing the o-ring. Greg. also PDI do the vacumn piston, this releases the back pressure off the round (just incase it the system causes suck back) thus helping to improve long range shots. Link to post Share on other sites
greg Posted May 14, 2009 Author Report Share Posted May 14, 2009 Figured a way to prototype this idea, to get max efficiency: 3/4" tap washers! I'm going to bore a few out to 10mm & stack them on the cylinder head with a bit of glue. This way I can reduce the cylinder by increments & record the power to see what happens. I wont have time to do this for a week but will keep you informed. Greg. Link to post Share on other sites
banjo Posted May 14, 2009 Report Share Posted May 14, 2009 That sounds like cracking idea, they'l also act abit like a buffer as well I did some research into barrel/cylinder volume balancing a few years back just before I did all my guns, and I found a Japanesee site that had a shed load of nice info on DIY gun upgrades, but sadly the link I have in my fav box seems to be broke or the site has disappeared into the eather , but anyhoo, after considerable testing in V2,V3 and an APS2 cylinder with different length barrels attached, they found the ideal volume of the cylinder is between 1.6 and 1.9 times the barrel volume, to take into account not only the blow by thing talked about above but also the 'squish' factor of compressing air behind a static bb before said bb starts to move. When I did all my calculations I went for a middle ground 1.7 and have never regreted doing it, I sadly did it as part of a load of upgrades so cant say whether it directly affected FPS or not, but it did make the rifle a bit quieter Link to post Share on other sites
greg Posted May 14, 2009 Author Report Share Posted May 14, 2009 That sounds like cracking idea, they'll also act abit like a buffer as well I did some research into barrel/cylinder volume balancing a few years back just before I did all my guns, and I found a Japanesee site that had a shed load of nice info on DIY gun upgrades, but sadly the link I have in my fav box seems to be broke or the site has disappeared into the eather , but anyhoo, after considerable testing in V2,V3 and an APS2 cylinder with different length barrels attached, they found the ideal volume of the cylinder is between 1.6 and 1.9 times the barrel volume, to take into account not only the blow by thing talked about above but also the 'squish' factor of compressing air behind a static bb before said bb starts to move. When I did all my calculations I went for a middle ground 1.7 and have never regreted doing it, I sadly did it as part of a load of upgrades so cant say whether it directly affected FPS or not, but it did make the rifle a bit quieter This might explain why I find the 500(ish)mm barrel the best bet in a vsr. If we are both right (Me thinking there is enough cylinder vol to go 800ish mm & you thinking 1.7), it may be that with a 500mm barrel the vsr is already at best efficiency & short stroking will only produce a negative affect. Any how the washers are 5mm thick so I'll record the results & let y'all know. I thought they'd make a good shock absorber too. Greg. Link to post Share on other sites
greg Posted May 14, 2009 Author Report Share Posted May 14, 2009 So for anyone who gives a darn, I just finished my short stroking thing: Took a stock vsr cylinder set (air break removed from the piston), mated it to two barrels (tn 509 x 6.04mm & lalax 430 x 6.03mm) reducing the stroke by 5mm & recording the results. I used 3/4" tap washers, which are 5mm thick. I bored them out to 12mm. Stacked them against the cylinder head using super glue to keep them in place. Did 10 shots& took the average. Long story short (bottom line), the fps went slightly down each time I took another 5mm away (added another tap washer) & then dropped dramatically at -35mm. With both barrels! & now the long story: TN,,, 509, stock 350, -5 348, -10 346, -15 344, -20 343, -25 342, -30 339, -35 313. Lalax 430, stock 345, -5 342, -10 341, -15 340, -20 337, -25 334, -30 332, -35 316. As the internal volume went down, so did the sound. Draw your own conclusions. Greg. Link to post Share on other sites
banjo Posted May 14, 2009 Report Share Posted May 14, 2009 I'm fairly sure you must be loosing compression due to the spare air trapped between the piston and cylinder head, in the 12mm hole in the washers On my cylinder I'm fairly sure the holes I have drilled in it are about 30mm from the front of the stopper slot, 62mm also rings a bell, and iirc that was the distance from the back of the cylinder head and damper pad to where the holes needed to be drilled. Oh, by the way I have a specialy modded 6.04 x 450mm systema barrel in. I still get all the quietness, but non of the lost fps,( I could possibly have gained some as the piston now has a chance to accelerate before it starts its compression, but I have no figures to back this up , its just speculation ), basically because the system still uses all the available air, but there is nowhere near as much spare air to make a noise after the bb has left the barrel, giving any unwanted muzzle report Link to post Share on other sites
greg Posted May 15, 2009 Author Report Share Posted May 15, 2009 I'm fairly sure you must be loosing compression due to the spare air trapped between the piston and cylinder head, in the 12mm hole in the washers On my cylinder I'm fairly sure the holes I have drilled in it are about 30mm from the front of the stopper slot, 62mm also rings a bell, and iirc that was the distance from the back of the cylinder head and damper pad to where the holes needed to be drilled. Oh, by the way I have a specialy modded 6.04 x 450mm systema barrel in. I still get all the quietness, but non of the lost fps,( I could possibly have gained some as the piston now has a chance to accelerate before it starts its compression, but I have no figures to back this up , its just speculation ), basically because the system still uses all the available air, but there is nowhere near as much spare air to make a noise after the bb has left the barrel, giving any unwanted muzzle report Yeah, I have to say (that although I am still sulking), venting the cylinder is my next 'project'. Unfortunately, I don't understand my results, so am having trouble getting my head around what is going on. This is obviously not just the relationship between the cylinder & barrel volume. If this were true, the results would have been different for the two barrels. I'm guessing it's down to the acceleration of the spring. the piston may need a 'run up' to achieve max velocity. Reducing the stroke is reducing the run up. You are right, a vent should help that. & that sudden drop off at -35mm, what's that about? Not sure what you mean about loosing compression? Do you mean air is leaking, or a reduction in volume? Greg. Link to post Share on other sites
AnotherJesus Posted May 15, 2009 Report Share Posted May 15, 2009 I'm guessing it's down to the acceleration of the spring. the piston may need a 'run up' to achieve max velocity. Reducing the stroke is reducing the run up. You are right, a vent should help that. Didn't someone mention that in relation to AEG cylinders already... I wonder who that could have been. Link to post Share on other sites
greg Posted May 15, 2009 Author Report Share Posted May 15, 2009 Didn't someone mention that in relation to AEG cylinders already... I wonder who that could have been. Yeah-yeah. Credit where credit's due. Mr 'Post #8 Clever cloggs'. But who spent 3 hours of his life opening the cylinder, adding another washer, shooting through the chrono, record the results, open the cylinder, add another washer etc. etc. Huh, Huh?????? I am such a mug. Greg. Link to post Share on other sites
AnotherJesus Posted May 15, 2009 Report Share Posted May 15, 2009 It's adding to the knowledge base. You're awesome, and we all love you. Group hug time. Great results by the way, well presented as always. Link to post Share on other sites
greg Posted May 15, 2009 Author Report Share Posted May 15, 2009 It's adding to the knowledge base. You're awesome, and we all love you. Group hug time. Great results by the way, well presented as always. *fruitcage* off. Greg. PS, aw, thanks. Link to post Share on other sites
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