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Old 03-08-2013, 11:01 PM #22
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.688 is what I use right now it's the only bore I have. I want to make my DM12 efficient for NPPL so I was reading Hesse threads for pointers and knowledge. I might pick up a .684 back in the near future. Didn't realize how much bore size affected efficiency.
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Old 03-08-2013, 11:06 PM #23
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Quote:
Originally Posted by JohnTrav View Post
.688 is what I use right now it's the only bore I have. I want to make my DM12 efficient for NPPL so I was reading Hesse threads for pointers and knowledge. I might pick up a .684 back in the near future. Didn't realize how much bore size affected efficiency.
to me 688 is just a perfect size, until it's either really hot or cold then you have to bore bigger. to prevent barrel breaks
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Old 03-08-2013, 11:12 PM #24
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I'm playing in 40 degree weather so it's a bit chilly right now. I'll have to do some tuning Sunday at the field and see how efficient i can get it.
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Old 03-12-2013, 08:12 PM #25
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Quote:
Originally Posted by 98Pro View Post
Lower coefficient of friction will allow less breakaway force meaning faster acceleration with less force. Less force does not mean less acceleration and also if the dump chamber seals then it means the gun has a metered amount of air... Most DMs end up shooting the whole dump chamber. So intact none of what I said was false. A polished bolt at 2.5 turns will still cycle faster than a a stock bolt at 3 turns. Proof: see how much lower you can set your dwell on the polished one opposed to the stock. It will be much shorter cause its average velocity is higher, meaning the air is released quicker and more efficiently. Will you be able to see the difference too much? Probably not, but it is there. Like others have said get an eigenbarrel they work amazing for efficiency. Like I said 7 pods on a pm8 with a 45/45 so you should net a good 10 with one. Hope lurker gets that eigenring soon for the 12+
I dont think you understand how air pressure works. the higher the pressure in any given space, the faster it will try to equalize. so less pressure means less violent equalization so yes in fact less pressure =less acceleration. there are so many experiments done to prove this is high school physics its not even funny. ( ya know... F=m*A) We see this manifest in the LPR. the bolt's speed will be directly correlated to the pressure output of the LPR. polishing the bolt does nothing to change how fast that air wants to expand. Its the speed of the air expanding against the bolt sail that drives the bolt. polishing the bolt only allows us to overcome newtons first law at a lower pressure. but remember that the air is also expanding slower. therefore the bolt also moves slower
Once we've overcome the bolts desire to rest, then a polished bolt will only help keep it moving easier. because bask to newtons first an object in motion wants to stay in motion. it has momentum. it takes more pressure to overcome the bolts resting state than it does to continue moving it. please tell me in what worlds does less force equal MORE acceleration. then prove it with math. if F=MA, then A=F/M.
If you have one Giant long can to test this you would see that it may take X pressure to get the bolt moving and y pressure to keep it moving and y will ALWAYS be less (and directly related to )X.
now that we know that, lest go back to your claim that a polished bolt moves faster. No matter what you've done to make that bolt smoother, it can never move faster than the air behind it. what that means is that at 75 psi, a stock bolt will move X fast. at 75 PSI a polished bolt will move the same speed. it is the air pressure that determines this speed.
your proof is using a paintball to determine how fast the bolt is moving. correlation does not equal causation.
If I take out a sock dm12 core, and drop in a polished one, you will see no difference to a minor one. the curve of acceleration is mush shorter than the distance the bolt travels. it accelerates, plateaus and moves at whatever speed the air behind it tells it to, then stops. Again the polishing only allows us to break away at a lower pressure (LPR) lengthen that curve (because lower pressure air equalizes less violently) and maintain it easier. that curve lengthening in combination with a slower bolt speed is what creates the smoother feel. the slower bolt also means the bumpers are hitting the can with less force too.

now about how much air is used in the dump chamber. no gun will EVER use all of it. thats what we call a vacuum. but lets say that we just call fully equalized air "all of the dump chamber air available"... saying that the DM fires on a metered amount of air is saying that you're using the exact same amount every time. if that were the case then dwell would have no effect on velocity. the dump chamber fills to approximately 145 PSI. the Dwell determines how long that 145 PSI has to equalize with the air in the barrel. more time means more pressure used. SO if it fired on a metered set of air. 18 MS would equalize to the same pressure as 21. it doesn't. we see it manifest in the FPS of the paintball. we all know that if you raise your dwell without touching your regs you will see velocity increases. that tells us that more air is being used with each ms. this will hold true until you've reached the point where either A the ball has left the barrel, or B until the air is equalized 100%. Id be willing to be with a much longer barrel we would see velocity increased in to the 30-40 ms. (translated it should take approximately 30-40 ms to completely equalize the dump). that number is an educated guess based on some other mechanical engineering I've done with regards to air pressurized actuators on robots when I was a student at the university of michigan.

short version : there is a set amount of air that could be used (about 4ci@145), but through dwell adjustments we can change how much air is used. we can let it equalize 10% (down to 131psi) with a VERY short dwell or it can equalize more like 50% (down to 77PSI) with a longer dwell. what those relationships are exactly I don't know, but its observable and provable that the dump chamber is not emptied every shot.

the original shocker bolts did not seal the dump chamber. when the bolt fired the barrel had a direct path to the HPR output. its why they created the HE bolt.


as for underboring and barrel breaks:
Im just going to leave this here. its just real world observable proof that underboring does not significantly increase barrel breaks.
methodology:http://www.punkworkspaintball.com/index.php?p=7&id=6
and the data :
https://spreadsheets.google.com/pub?...sMnf44CEWQxNDA
and another one showing that under boring will increase you velcity consistency.
https://spreadsheets.google.com/pub?...en&output=html

its odd to me that you're a lurker fan and don't read punk works, or know about lurker's penchant for using a 679. I will use a 682 or 684 this weekend in dallas. paint should be around and 88.
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Last edited by TherealInsomniac : 03-12-2013 at 08:17 PM.
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Old 03-13-2013, 06:45 AM #26
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Just so you know under boring falls apart around 6 or 7 thou for semi auto play. Once you hit a critical squeeze level you get seam pops.

Source: feedback from 1000s of barrels sold
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Old 03-13-2013, 07:26 AM #27
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Originally Posted by 98Pro View Post
Lower coefficient of friction will allow less breakaway force meaning faster acceleration with less force.
Maybe a nit-picky thing here, but typically in oring data the friction coefficient relates to the running friction, not the breakaway friction. The difference being that typically the higher durometer will have a lower running friction number yet a higher breakaway friction due to the compression/ "squeeze" of the oring.
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Old 03-13-2013, 09:07 AM #28
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Quote:
Originally Posted by Lurker27 View Post
Just so you know under boring falls apart around 6 or 7 thou for semi auto play. Once you hit a critical squeeze level you get seam pops.

Source: feedback from 1000s of barrels sold
In lots of paint, the seam width is different then the off seam width. I'm wondering which is the more critical measurement. Should I underbore relative to the biggest seam or the smallest one (or shoot the middle)?

The last paint I got was off by as much as 4 thou difference between the seam and the off seam... depending on the underbore sizes that you have available, you could, easily, get in the danger zone by trying to underbore the minor width. In that case I just went with a nice overbore, to be safe. I'd be interested to see some data on ob-long paint going through different underbores and seeing if there was a difference in break frequency... but that would be a hellofa crappy test to conduct.
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Old 03-13-2013, 09:21 AM #29
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I tend to think of it as the seam diameter because i tend to find what matched is for the day with barrels or a sizer and adjust from there.

Not sure to what degree very oblong paint increases tolerance to squeeze
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Old 03-13-2013, 12:47 PM #30
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I ended up never using my .680 barrel. I sold it and run only 684 now unless the paint is huge, then I use my 692 and deal with the loss of efficiency.
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