Sev Posted November 26, 2018 Share Posted November 26, 2018 Hi Whilst contemplating the barrel group options for a build in progress, I came upon a question I can't work out the answer to. In this build I have a cylinder with 23.8mm internal diameter and the piston stroke is 46mm. With the current 6.05mm 280 mm barrel that gives me a ratio of 2.54:1 which is close enough to the limit of 2.5:1. Luckily this build is for CQB and typical field play combined, so that'll work nicely, I think. My question comes with longer-barrelled builds. I've read that longer barrels favour a higher ratio (between 2 and 3.5) because the detrimental effects of a low ratio are exaggerated. The thing is, by my calculations, with a 6.03mm 370mm barrel you would need a stroke of 61mm to hit 2.5. If you tried that in a fast, torque-based DMR build, which is likely short-stroked, how do you gain that extra cylinder volume needed? Either my maths is wrong, my information is wrong or people using longer barrels are running seriously sub-optimal with high-tuned setups. Which is it? Link to comment Share on other sites More sharing options...
Immortal Posted November 26, 2018 Share Posted November 26, 2018 Say whaaaaaat?! I wish I understood this ratio stuff. I need to learn this! Link to comment Share on other sites More sharing options...
Supporters Adolf Hamster Posted November 27, 2018 Supporters Share Posted November 27, 2018 The short version is you don't short stroke a long barrel build. Link to comment Share on other sites More sharing options...
Sev Posted November 27, 2018 Author Share Posted November 27, 2018 On 27/11/2018 at 00:38, Adolf Hamster said: The short version is you don't short stroke a long barrel build. Expand Ok, makes sense on reflection. How would you avoid PME without shortstroking? The reason I'm keen to understand is that I am planning a DMR build for my next project :D Link to comment Share on other sites More sharing options...
Supporters Adolf Hamster Posted November 27, 2018 Supporters Share Posted November 27, 2018 On 27/11/2018 at 09:23, Sev said: Ok, makes sense on reflection. How would you avoid PME without shortstroking? The reason I'm keen to understand is that I am planning a DMR build for my next project Expand if you're running a higher fps then you'll get away with it naturally, otherwise you just accept the trade off in speed, if it's a proper dmr you're not really gonna be using full auto anyway. Link to comment Share on other sites More sharing options...
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