Hangtight Posted January 8, 2018 Share Posted January 8, 2018 I've just spent an interesting couple of hours cutting a barrel down 30mm at a time to try and get a proper answer to the correct cylinder /barrel ratio for a few different BB weights, and I thought I'd share them here. The test was done with a single gun, using an M100 spring and a cylinder with a 12mm port for a compression distance of 48mm in a 23.8mm bore cylinder. I cut and roughly crowned the barrel by 30mm each time. It was not disassembled from the hop, and neither was the hop setting changed at any point. I fired a string of twelve shots for each BB weight at each barrel length to give an average and a deviation. 460mm barrel (ratio 1.60:1) 0.2g 356avg, +/- 5 0.25g 324.9avg, +/- 7 0.28g 305.1avg, +/- 3 430mm barrel (ratio 1.73:1) 0.2g 357.1avg, +/- 5 0.25g 326.6avg, +/- 4 0.28g 305.8avg, +/- 2 400mm barrel (ratio 1.85:1) 0.2g 358.7avg, +/- 3 0.25g 329.0avg, +/- 3 0.28g, 304.5avg, +/- 1.5 370mm barrel (ratio 2:1) 0.2g 353.6avg, +/- 2 0.25g 322.4avg, +/-1.5 0.28g 301.9avg, +/- 1.0 340mm barrel (ratio 2.2:1) 0.2g 348.9avg, +/- 1.5 0.25g 321.0avg, +/-1.5 0.28g 301.0avg, +/-1.0 It would appear that the ratio that gives the best efficiency is not necessarily the same as the one that gives the best consistency. More volume would appear to be better than not enough. So the numbers I've been quoting for cylinder ratio have been out, but the barrel lengths I've suggested for say, a full cylinder and 0.28g BBs have been about right. In general, it would seem that a full AOE corrected cylinder is well matched with a 363mm barrel and 0.28g BBs. I might carry on cutting down the barrel and get some more figures, but it's a nice quality TM one, and now it's about the right length for one of my project guns. Link to comment Share on other sites More sharing options...
Hangtight Posted January 8, 2018 Author Share Posted January 8, 2018 Couple of extra numbers... Piston weight is 26.1g and there is a bearing on both the guide and the piston. There's probably another 10fps in there as this is a well used gun that could really do with better lubrication. It was put together with white lithium grease before I knew any better. Link to comment Share on other sites More sharing options...
Davegolf Posted January 8, 2018 Share Posted January 8, 2018 Interesting, is that a type B cylinder, as in the ports break out the rear of the cylinder? Still relative results even if the gearbox internal spec could be costing you a few FPS Link to comment Share on other sites More sharing options...
Beowulf Posted January 9, 2018 Share Posted January 9, 2018 Wish you could have started with a longer barrel for snipers Link to comment Share on other sites More sharing options...
Hangtight Posted January 9, 2018 Author Share Posted January 9, 2018 If anything, sniper rifles actually need shorter barrels. The heavier BBs need a higher cylinder/barrel ratio. For 0.43g, a ratio of 2.9:1 is suggested. Just like AEGs they only have so much cylinder volume, so for the ratio to increase, the barrel length has to be reduced. Some of the most accurate spring sniper rifles have barrels around 300mm. Link to comment Share on other sites More sharing options...
Davegolf Posted January 9, 2018 Share Posted January 9, 2018 Hangtight would have had to start with a sniper rifle though not an AEG?? A VSR type rifle should have a much longer barrel to suit the larger cylinder available to that platform Link to comment Share on other sites More sharing options...
Supporters Sitting Duck Posted January 9, 2018 Supporters Share Posted January 9, 2018 Soz to crash but have I read the cylinder window (12mm) is 48mm from front ??? subtract 15 from 48 = 33 & multipily by 10 = 330 330 is a rough guide to matching up barrel lengths to cylinder (giving you aprox 2.0:1 ratio dooberry give or take a smidge) NOTE NOT 12MM BUT TAKE OFF 15MM FROM 48MM = 33 OR 330 BARREL AFTER X10 see here but the post I created a while back at the very end I revised the 12mm figure to 15mm (basically to allow a bit more I found for piston releasing & pressure to start building) WARNING - NECRO POST ALERT !!!! Those volume ratio calculators & even the pic of cylinder ports to M4 carbine are a bit confusing plus the 2/3 or 3/4 or 4/5 bollox is open to interpretation I thought at times - sod measure, minus 15 & x 10 Same as gear ratio malarky counting/pulling teeth - just multply the bevel turns by 3 than f*ck about loads Not quite 101% of exact volume ratio this (X -15) x10 method gives out At time of writing I was guessing @1.6 maybe 1.7 then this forced me to revise to 15 not 12 Still a bit sad looking at things in my OCD way but not quite as bad as I used to (the medication is at last starting work) Anyway good guide/test results sir especially the figures and levels of fps variation nice one Link to comment Share on other sites More sharing options...
Supporters Esoterick Posted January 9, 2018 Supporters Share Posted January 9, 2018 5 hours ago, Hangtight said: If anything, sniper rifles actually need shorter barrels. The heavier BBs need a higher cylinder/barrel ratio. For 0.43g, a ratio of 2.9:1 is suggested. Just like AEGs they only have so much cylinder volume, so for the ratio to increase, the barrel length has to be reduced. Some of the most accurate spring sniper rifles have barrels around 300mm. This seems contrary to what is commonly recommended on both the VSR owners facebook group and Airsoft sniper forums, which is to use a 430mm barrel even in a G Spec when using weights around 0.40g Link to comment Share on other sites More sharing options...
Davegolf Posted January 9, 2018 Share Posted January 9, 2018 430 is pretty golden on performance for a 500fps BASR. @Sittingduck that's a cool way of thinking to quickly work out barrel length, I think that 12 was better than 15, actually 11 because 11 gets you in the 2.1/2.2 ratio zone which is best for 330-360fps, gives max joule creep with least spring effort or over volume. Link to comment Share on other sites More sharing options...
Supporters Sitting Duck Posted January 9, 2018 Supporters Share Posted January 9, 2018 A G&G SR25 has a std cylinder not a proper longer 2.5 cylinder like SVD & L85 19 tooth thingy's In THEORY they should only be using a 455mm barrel in that sense But they can use a 510mm if setup REALLY WELL but it is pushing the volume imho Ideally for say 550 barrels you will need a longer cylinder like the v2.5 SVD L85 But even then I would not go beyond 610 barrel The volume thingy is still open to debate but the general guide is to stick with an aprox vol ratio (depends on bb weight but again it will vary a little plus the odd one that works but perhaps pushes limit) TBH I stopped studying this stuff way too much, it is open to everybody's take and instances that break mould I got a rough - and I say rough idea or method to avoid doing PhD maths n crap on gears & cylinder/barrels It seems to kinda work (so far) so I'll still continue to use an easy rough n ready reckoner on very short (mp5k) or very long (AEG SVD/L85) the correlation may not be 101% perfect but in general it works (well I think so - so far) Link to comment Share on other sites More sharing options...
Supporters Sitting Duck Posted January 9, 2018 Supporters Share Posted January 9, 2018 7 minutes ago, Davegolf said: 430 is pretty golden on performance for a 500fps BASR. @Sittingduck that's a cool way of thinking to quickly work out barrel length, I think that 12 was better than 15, actually 11 because 11 gets you in the 2.1/2.2 ratio zone which is best for 330-360fps, gives max joule creep with least spring effort or over volume. It depends on a few factors - you can correct the AoE perfectly or slightly over-correct or under-correct The Correcting of AoE bang on or smidge over/under "can" effect the stroke/volume more than any bore-up crap imho On the piston's release it is completely static,will need to accelerate to final speed the o-ring hasn't even begun to seal let alone compression starting to build properly So there must be a good 5mm of travel before any power is actually generated Hence I gave it a few more mm's to allow for the power to build from nothing As I say it open to everybody's take on stuff and stuff will vary but the maths of cylinder barrel ratios even on a easy to use online airsoft calculator or a tiny little app is open to variations or interpretation or perhaps I think hmmm nahhh I just noticed there was some correlation to gear ratio checking and also the dimension of the port to barrel it is supposed to be paired with tweak it all how you see fit but just gave a rough basic guide to consider as a foundation perhaps nothing I ever say should be taken as 101% Gospel as I often talk out of my ar$e Plus we are ALL still learning with every build - so nothing I say is set in stone Link to comment Share on other sites More sharing options...
Davegolf Posted January 9, 2018 Share Posted January 9, 2018 Totally, for the most part any additional AoE will decrease your swept volume. Youve probably noticed that unless you run a long ass barrel a full cylinder normally reduces FPS because the the piston cannot get a 'run up' to gain some speed before meeting cylinder pressure resistance. Ive found where full volume is needed a type B usually out performs a type A, whether that's down to faster piston acceleration or better piston sealing early in the strike due to the more aggressive cylinder pressure who knows. like you I can't be arsed with the math but trial and error proves what works Link to comment Share on other sites More sharing options...
Hangtight Posted January 9, 2018 Author Share Posted January 9, 2018 Total piston stroke after AOE adjusted is 60mm. The port is 12mm, so the piston only compresses air for a stroke of 48mm. Working out the ratio for each BB weight at the point where the fps variation gets really nice and small, I get 0.2g 2:1, 0.25g 2.2:1, 0.3g 2.4:1 (extrapolating a bit). This pretty much matches as a linear increase with the suggested ratio of 2.8:1 for 0.4g in spring sniper rifles. Which is about 450mm in a VSR and just over 400mm in a L96 (been a long time, had to go and check. ) Link to comment Share on other sites More sharing options...
Davegolf Posted January 9, 2018 Share Posted January 9, 2018 Yeh those ratios per weight are the perfect starting point and get you so close to where you need to be, then if you want to / can be arsed to chrono at your desired BB weight vs 0.2 reference to get as much joule creep as possible, that way you know you are transferring the maximum amount of energy into your little ball of shootyness Currently got my NGRS Scar at 2.17 with 0.28s with no loss of energy from 0.2s Not only does a gun shoot nice when all is matched it sounds so stress free as there's not tons of extra air blasting out the end of the barrel or the piston hammering the cylinder head because of lack of volume. Satisfying Link to comment Share on other sites More sharing options...
Hangtight Posted January 9, 2018 Author Share Posted January 9, 2018 That was one of the things that was most noticeable as I shortened the barrel... Just how much the shot cycle smoothed out as you got closer to the 'right' ratio. I must be doing something right, cos I hit what I aim at, and from far enough away to be accused of cheating! Link to comment Share on other sites More sharing options...
Supporters Sitting Duck Posted January 10, 2018 Supporters Share Posted January 10, 2018 Long story short.... One day if/when you get a chance, pop the top receiver say Then take a pic maybe of port with the dimension of front of cylinder to port Basically the front of cylinder to red line or front end of port please if you can We can call this distance X before we get into geeky world Just trying to see if the amount to subtract from X is 10, 12, 15 or so before multiplying by 10 More trying to see if my theory works out and if we can use a rough ready reckoner Than a calculator or app A good one is here: https://www.cynosurex.com/Software/AEG Compression Volume Calculator/ because you can mess about with figures and ratio updates as you adjust crap The stroke of 60mm might be an absolute max on AoE it could be 58 at a smidge over 12 o'clock (normally it is about 12:30 position but everybody has their acceptance of total perfection or acception) A non AoE piston you got say 4mm or so extra stroke making 63 or 64mm stroke The stroke even just a couple of mm will effect volume possibly more than any bore up kit (mess about in calculator and see it do its maths magic on exact same gun) hence to DMR mofo's sinking money into bore up kits, probably best just partially correcting AoE Anyway - soz for waffle, great test - if you get a chance post a pic with dimensions of port to cylinder head then I/we might have idea what to take off in a rough ready reckoner (please - with sugar & cherry on top) Link to comment Share on other sites More sharing options...
Davegolf Posted January 10, 2018 Share Posted January 10, 2018 Think it's worth making it clear AoE has nothing to do with volume adjustment primarily, but the more AoE you run wether it's behind the piston (old stylee) or sorbo on the cylinder head (current style) will reduce the available swept volume as a by product of its actual function. All standard cylinders are 72mm total in length. Pretty much all cylinder heads take up 6mm of that when fitted. Now we have 66mm available. Next a standard piston takes up another 6mm when fully cocked / rearward. Now we have 60mm available, the maximum swept volume possible with a type 'A' eg 'unported' cylinder. Any amount of AoE wether it's added to the cylinder head or the piston head will reduce this swept volume. Link to comment Share on other sites More sharing options...
Davegolf Posted January 10, 2018 Share Posted January 10, 2018 Here's my NGRS Scar. Red line is 53.5mm (type 'C' ported cylinder) Blue line is 10mm (6mm cylinder head with 4mm sorbo protrusion) So dimension 'X' is 43.5 X minus 11 times 10 is 325 Which is very close IMO to the right barrel length for 2.1 - 2.2 volume ratio @ 330-360fps But as you say is speculative. I mean you could strip it right back to a simple rule, barrel length is equal to FPS once you're running at or above 1j / 330fps. Then use your X tool to determine correct cylinder volume. You could work out a multiplier for different fps levels and respectively BB weight. Link to comment Share on other sites More sharing options...
Davegolf Posted January 10, 2018 Share Posted January 10, 2018 PS I'm proud of the straight finger painted lines In fact that's a worthy achievement right there I could happily go to bed now knowing the day wasn't wasted Link to comment Share on other sites More sharing options...
Supporters Sitting Duck Posted January 10, 2018 Supporters Share Posted January 10, 2018 I would have said 53.5 - 15 = 38.5 x 10 = 385 cylinder port would ok to use for up to 385mm barrel That was what I did the rough ready for What I'm trying to do is say we increase the amount to subtract (originally about 10mm is where the piston head rests on cylinder head) SAY we did 53.5 - 20 now = 33.5 then x 10 = 335 then this would be the newer setting to use up to a barrel length of 335 with a higher barrel/vol THIS is why I'm asking Hangtight to display his port position OR if you can list the length of your barrel in the SCAR perhaps This way it can refine or improve a rough ready guide for say a decent-ish 2.0:1 guide without going done the calculation route or trying a shorter barrel to improve the vol I'm just trying to see if the rough guide subtraction amount or Y or whatever can helped to be refined that was all To sum up you took off say 10 where head+sorbo was then took off 11 then x 10 etc.... What I started with was just 12 only then went to 15 to subtract there was only really one figure to subtract then x 10 etc..... (just to keep it as simple as possible I guess) I then revised this to 15mm (still lower than your 21 (10 then 11 subtraction) as 12mm was producing say 1.65 ratio so 15mm produces a more 1.8 ratio Which according to some guides is acceptable but I have reservations.... according to this even 1.42:1 is acceptable but I think that is bollox on PDI AK47 hence me trying to push for 1.75-ish at least or 1.8:1 with revised 15mm number to subtract now if that needs to increase to (X - 20/25) x 10 = ideal barrel for a 2.0:1 then fair do's Now with both your gun & Hangtight's testing you are happy with a a ratio of 2.1 - 2.25 ish Soooooooooooo if you inform us of your barrel in SCAR & Hangtight posts the pic/dimensions of his cylinder porting THEN it might be a straightforward of say 53.5 - 22.5 or something = 310 x 10 = 310mm barrel eg: sunbtract 15-ish for 1.8:1 ratio 20-ish for 2.0:1 ratio 25-ish for 2.2:1 ratio see what yields best results in shooting or proof of pudding then it might provide a fairly accurate rough/ready guide in seconds than try to enter & calculate all the variables cylinders don't vary that much and tbb Vs reg decent barrel of say 6.05 or bore up kits do not effect the final vol results THAT much excluding very wide bores or AEP cylinders most stuff is within a regular margin but the stroke just by a couple of mm can start to impact ratio a fair bit so trying to put or refine an easy checky thingy majig based upon port position etc... Link to comment Share on other sites More sharing options...
Davegolf Posted January 10, 2018 Share Posted January 10, 2018 The Scar barrel is a 6.05 320mm Link to comment Share on other sites More sharing options...
Supporters Sitting Duck Posted January 10, 2018 Supporters Share Posted January 10, 2018 25 minutes ago, Davegolf said: The Scar barrel is a 6.05 320mm Cheers - so it means that 53.5 distance if we take off 20 in total or so will give perhaps 335 @ on about 2.0:1 or a bit more vol on a slight shorter barrel or take off a bit more in calculating prior to x10 for higher volume heavier bb's So even my revised 12 to 15 seems incorrect if you seek a 2:0:1 ratio 15 might be ok for 1.75:1 volume but shooting tests might still not be ideal (like I said some of the stuff written like 1.47:1 ratio I thought was way too low tbh) as yourself & Hangtight find a ratio of 2:0:1 upwards better then perhaps the subtraction figure or Y needs to be 20 or a bit more X = port distance Y = value to subract (15 for 1.75, 20 for 2.0 or 25 for for 2.25:1) Z = barrel length (X - Y) x10 = Z (kids remember brackets or equation will be wrong as multplication takes priority over addition & crap) F*ck me my head hurts - this was supposed to simplify it but as per usual I've made way more complicated than it needs be Link to comment Share on other sites More sharing options...
Davegolf Posted January 10, 2018 Share Posted January 10, 2018 Lol! Yes I think the lowest ratio that actually performs seeing as this is what people would be considering or calculating this for in the first place is 1.9 Lots of us have arrived at a similar conclusion by our own testing... General consensus for AEG's is; 0.20g = circa 2.00:1 0.25g = circa 2.20:1 0.30g = circa 2.30:1 Link to comment Share on other sites More sharing options...
Hangtight Posted January 10, 2018 Author Share Posted January 10, 2018 I'll do the maths in a bit, but it should be possible to come up with a really simple formula that you just put the BB weight and port position in and the approximate barrel length falls out the other end. Link to comment Share on other sites More sharing options...
Sako Posted January 24, 2018 Share Posted January 24, 2018 So while just randomly looking online I found this handy website (loads of items covered, such as modifications, rebuilds, how-to guides), but at the bottom of the ‘calculations’ page is a volume/barrel ratio calculator - handy for any quick references. http://airsofttech.dk/Calculator.cshtml Link to comment Share on other sites More sharing options...
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