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Old March 13th, 2017, 23:17   #1
BobbyDangerous
 
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Ported cylinder

I have an SHS ported cylinder now and I get a decent FPS with a 363mm inner but when I switch to a 260mm FPS drops significantly. Any recommendations on what sort of ported cylinder I need for a shorter length inner barrel?
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Old March 14th, 2017, 01:40   #2
Hectic
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this should help out.
http://s253.photobucket.com/user/air...sdsad.jpg.html
but based Ún the chart depending on the port location you could be optimal. but losing because of the light bb, try to chrony for Juels not fps.
also could just be airseal between the new barrel and hop rubber or hop unit etc..
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Old March 14th, 2017, 02:44   #3
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You've got too much volume to push out a light BB. I assume you're using .20s to chrono with the 260mm?
The BB is leaving the barrel before the air even gets a chance to really compress itself. So try chronoing with a .28 or .30 first.
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Old March 14th, 2017, 10:05   #4
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chrono value with a .2 doesn't matter as long as it is under 400 fps. The important one is you get the value you want with whatever weight you're shooting. 400 fps with .2 is 1.48J Ideally you want to shoot 1.48J with the weight you actually use. In a perfect world when you get 1.48 with a .2 the math says you will get 325 with a .3, but in your situation, you could have a phenomenon called joule creep where you have too much air in the cylinder compared to the barrel, so a heavier BB might get higher J than a lighter one.

I would check that before making any changes to the system. If you are getting acceptable J out of this setup with your shooting weight, then nothing needs changing.

If you're getting low readings, finding an even shorter ported cylinder might be a challenge, you could just drill a slot closer in if you know what you're doing... or you can find the right cylinder... or you can use a stronger spring. If you're going to change between short and long barrels, maybe it's best not to change anything.
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Old March 14th, 2017, 12:32   #5
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Chrony with .25's.

With an m110 was roughly 290 with the short barrel

340 with the 363
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Old March 14th, 2017, 13:04   #6
lurkingknight
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that sounds not quite right.. I'm pretty sure you should still be getting over 1J.

Check your compression.
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Old March 14th, 2017, 13:11   #7
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that sounds not quite right.. I'm pretty sure you should still be getting over 1J.

Check your compression.
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Old March 14th, 2017, 13:31   #8
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Originally Posted by BobbyDangerous View Post
Chrony with .25's.

With an m110 was roughly 290 with the short barrel

340 with the 363
I think it's the inner barrel itself. The 260mm has a large window. Think it's not right for my hop up. I'll try cutting down my other barre and working with that.
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Old March 14th, 2017, 15:11   #9
lurkingknight
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window shouldn't matter. Don't cut your barrel unless you have the tools to redo the crown on the end.
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Old March 15th, 2017, 10:47   #10
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Yeah I used a pipe cutter and a dremel.
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