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Thread: Idea on blowback/chop design

  1. #1
    Join Date
    May 2001
    Perth, WA, Australia

    Idea on blowback/chop design

    It's a quiet day today and I've been thinking, what with the recent posts from AGD about a new RT valve with a longer bolt design and their research into the blowback/chopping situation being related to the barrel id.

    (May need to read carefully as these ideas are just popping around in my head)

    I was thinking, even if AGD brought out the new valve with the much longer powertube/bolt design, wouldn't it still be susceptible to blowback anyway. If the bolt design will still remain the same except longer that is, when the bolt is released the release of gas is almost instantaneous and would shoot out to the front of the bolt very quickly and wouldn't allow the bolt to travel in far enough into the barrel.

    Ok I was thinking about the powertube spacers and the different sizes. Wouldn't the smallest powertube spacer produce less blowback than a larger powertube spacer, by increasing the distance the bolt needs to move forward before it clears the powertube o-ring to release the gas. In effect allowing the the bolt to travel further forward into the barrel. Of course the differences in size between powertube spacers is small and would probably not have that much of an impact at all. But what if we magnified the size differences, say 1cm difference or more from one spacer to the next size down/up. That I believe would have some sort of effect.

    (I hope I'm making myself clear)

    Now from what I just said, what if we alter the bolt design a little bit. What if we extended the bolt stem, ie make it longer. like below:

    |---------------------------------| <-- Extended Bolt Stem

    So basically the extended bolt stem would partially be inside the air chamber.
    By doing this it should allow the bolt to travel further into the barrel before releasing the gas, and result in less blowback. As the distance for the bolt stem to clear the o-ring would be increased, and hence the time for the gas to be released through the bolt. And the good thing would be that you can still use your current valve.

    How about a combination of the extended bolt stem and a much smaller powertube spacer? Within reason, obviously as the bolt can only move forward so far.

    I may be totally way off course here.
    Last edited by st6212; 09-26-2001 at 07:43 AM.

  2. #2
    Join Date
    Nov 2000
    Mobile Al, USA
    well, i see what your geting at. And, as i was thinking about it, it sparked another question in my mind. "where is this blowback gas comming from?" I could think of two possible solutions: 1. that it was primiairly from the front end of the bolt- - and blowing back up the breach because of the bolt clearing the breach too fast. a longer bolt should help this problem, and apparently it has, a little bit. Why not completely, though? Thats when I started thinking about another answer to my original question=== 2. what if the blow back gas originates primairly from the back of the bolt? Ill try to explain my line of reasoning. . . when the gun fires and th bolt clears the power tube o-ring, most of the gas is expended directly out through the front of the bolt, effectivly taking the champered paintball with it. Is this 100% of the gas released? i dont think so. . . what if, when some of the gas released flowed up through the power tube, but didnt make it out the front of the bolt- -- what if it backflowed between the inner wall of the bolt and the outer wall of the powertube-- flooding next around the outside of the bolt, from the bottom up. this expanding gas would affect the pressure immediately above the bolt(where the next paintball is resting) potentially exerting a force on the next ball i.e. blowback. a longer bolt would not stop this. considering the way gases behave under pressure, i believe this is completly possible- - - there are no airtight seals in the are i just described. the amount of blowback experienced would vary depending on the amount of space available between the power tube and bolt, as well as the amount of available space between the outer lip of the bolt base and the inner wall of the mainbody. All of these variables would explain why some people report "problems with chopping due to blowback", while others do not- - - - it would be a combination of the specific tolorences to which the bolt, powertube, and mainbody meet. . . different production runs of these parts would surely NOT be completly identical- - - in the sense of open spaces that a gas could flow through- - - it really wouldnt take much space at all.

    now, assuming that tom and the folks at AGD know what im talking about, and they test and verify this, the nect logical question would be "how does one fix it". well, simply put, prevent the air from either 1. escaping from the back of the bolt, or 2. preventing all of this escaped air from ever coming around the bolt to cause problems. I dont think that the first solution is really practical, considering that i believe the second could be so much eaiser to fix.

    theres a couple of ways this could work.

    1. (i started thinking about an autococker bolt, w/ the 2 o-rings which ensure the gas maintains its intended path.)
    what if you could put an oring or some type of seal on the outer lip of the bolt base. . a moving seal (like the orings on the 'cocker bolt) that would prevent any escaped gas from coming pass from the outside base of the bolt. . additionally, this would indirectly ensure that more of the gas was directed out the front of the bolt- - potentially increasing gas efficency.

    2. place a seal in a machined groove on the inside of the mainbody. . at the point at which the bolt base stops in its forward movement. this would accomplish basiclly the same thing, but would be more expensive to implement. However, it should work longer than choice #1, because the oring itself woul not move. . it would be basiclly the same kind of seal that exists between the powertube oring and the bolt stem. it would seal this back area offonce the bolt reaches its fully extended point. another downside is that you would still have some escaped gas - - from when the bolt stem clears the power tube oring, but before the new mainbody oring engages the bolt base. - - - so, results might not be that great. . once agiain this would have to be tested.

    3. Place the oring seal inside the bolt. . . it would be located at the base of the bolt, and would engage the outside of the power tube - - providing a very effictive, moving seal == directing all the expanding air out of the front of the bolt

    So, in conclusion, I propose that an additionally modified bolt would be most effective in solving this problem. perhaps one of the extended nose bolts, with an oring around the inside base of the bolt.

    one last thing -- - all this is just some random ideas floating through my head that have started this theory. . . . so, if ive missed somthing completely obvious, please point that out to me.

    Additionally, I hope everything makes sense.. . its like 2 am here, and im tired. will be glad to clarify anything that sounds weird when my brain is working properly.

    -- CARL

    P.S. if you think about this, it also accounts for the barrel question. . the id of the breach end of the barrel will either allow a larger gap for air to pass through from the rear of the bolt, or a smaller gap. . once again explaining why some people report exceptional problems, and others do not. . . if you had a barrel that the breach was just a little too short, and the id was a little big, comined w/ loose tolorences inside the mainbody, with a bolt that didnt seal off on the OUTSIDE of the powertube. . youve created a hiwaay for gas to flow out the back of the bolt, around the front ring in the mainbody, either and flood the breech area. . . == blowback problems.

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