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adjustable rate of fire for BBMGs?

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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Unread postAuthor: ammosmoke » Wed Apr 02, 2008 1:11 am

jackssmirkingrevenge wrote:This is a misconception - the vortex is only there to aid feeding, it's the pressure accelerating the BB down the barrel that gives it its velocity. If what you were saying were true, why bother with a barrel at all?


Because it helps with accuracy? XD JK. Anyways, venturi effect anyone?
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 02, 2008 1:48 am

Joking apart, it's frustrating to see people think they can dramatically increase the performance of a BBMG just by playing around with chamber configurations. If you want to up the power, use as long a barrel as you can manage, with the maximum flow of gas into the chamber and up the pressure - Brian certainly had the right idea.
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Unread postAuthor: Lentamentalisk » Wed Apr 02, 2008 2:33 am

so almost all of the air that comes out of the inlet goes straight to the barrel? If that is the case, I find it quite interesting that it will forgo neutralizing a pressure gradient so completely in order to keep its momentum. Is that the case, or is there actually a lot that slips out?
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 02, 2008 2:46 am

As far as I've seen, there is no discernable difference in terms of muzzle velocity between a vortex or cloud BBMG that have the same barrel length, pressure, valve and chamber volume.
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Unread postAuthor: Lentamentalisk » Wed Apr 02, 2008 2:49 am

so is there any reason for anyone to go through all the extra work of making a vortex, when a could works just as well?
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 02, 2008 2:54 am

It's a feeding issue more than a performance one.
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Unread postAuthor: Lentamentalisk » Wed Apr 02, 2008 2:58 am

gotcha! Wow it makes a lot more sense to me now! Thanks for clearing up that whole thing.
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Unread postAuthor: Davidvaini » Wed Apr 02, 2008 3:39 am

ROF will increase with a vortex over a cloud but as Jack said velocity isnt really increased... its such a small difference in velocity but ROF is greatly improved..
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 02, 2008 3:55 am

Davidvaini wrote:ROF will increase with a vortex over a cloud


I was under the impression that it was the other way round, as the vortex tends to add a "mechanical delay" to the feeding process.
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Unread postAuthor: Davidvaini » Wed Apr 02, 2008 4:01 am

nope... since the air spins it acts kinda like a tornado in which it actually sucks in the bb's faster than a cloud... A cloud is exactly like the name suggests... a cloud of bb's that get sucked by a straight vacuum...

A spinning vortex of air will actually have more suction with the same amount of pressure than a straight vacuum would (cloud)...

Also another misconception is that ROF increases with a shorter barrel... Once the bb leaves the vortex it has already been fired... the barrel just acts as a straight passageway for the bb to travel... Though barrel length doesn't change ROF it will effect velocity.

You will get a higher velocity and better accuracy the longer the barrel... but If you go too long you will get friction which will actually decrease velocity...

The higher the pressure being used the longer the barrel you can go without hitting friction... With pressures around 120PSI I have found that with a standard inline vortex it is best to have your barrel at around 12-14 inches.. When you start to increase that to higher PSI such as with the unregged co2 inlines that people are making now you find that your optimized barrel length is longer. Depending on how "tight" your barrel is your coefficient of friction will vary.

The only time a shorter barrel would increase ROF is if you have a gas blow back cycling issue cause from too much recoil.

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Unread postAuthor: bob-a-lu » Wed Apr 02, 2008 6:04 am

this could work but you would have to find a really weak spring because if you use a pen spring it could be too tight and wont let the flow of bbs through thus getting a jam and wasting time and air.
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 02, 2008 6:21 am

Davidvaini wrote:Also another misconception is that ROF increases with a shorter barrel... Once the bb leaves the vortex it has already been fired... the barrel just acts as a straight passageway for the bb to travel...


I disagree, the next BB is sucked into the barrel because the previous one has left the muzzle, causing the pressure to drop and a subsequent rush of air down the barrel. When the barrel is shortened, this process takes less time and the rate of fire therefore increases.

this could work but you would have to find a really weak spring because if you use a pen spring it could be too tight and wont let the flow of bbs through thus getting a jam and wasting time and air.


That's the point of having the bolt to adjust spring strength ;)
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Unread postAuthor: c0rpse » Wed Apr 02, 2008 10:04 am

Is it that bbmg's like clouds and vortexs are inefficient or they just shoot so fast you need a large volume of air to shoot them for more than a few seconds? I am trying to decide whether I should build a launcher based on ant's hammer valve auto principle or try this adjustable detent system. I really like the simplicity of the bbmg, but I know for a fact that the hammer valves are efficient. I would just rather stay away from making a sear for a trigger.
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 02, 2008 10:53 am

Using a detent should technically make it much more economical with air, as flow is highly restricted (not a perfect seal but leaks will be minimal for a tight-fitting barrel) when the BB is held by the detent. Also, you should get a benefit in terms of muzzle energy, as the delay will allow more pressure to build up behind the BB before it's fired.
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Unread postAuthor: Davidvaini » Wed Apr 02, 2008 11:46 am

I have played around with different barrel lengths and I have found that ROF doesnt get changed... the air flow is constantly putting pressure behind the bb and therefor it doesn't slow down.. the main force for the reason the bb is going in and out of the barrel is not because of suction but because of the air pressure that is being presented inside the vortex and the pressure behind the bb being pushed... Its mainly the push of pressure behind the bb that causes it to be fired the only time "suction" has an effect in a vortex is when its in the actual act of spinning... the vortex of air will cause a suction force that carries the bb's into the stream of air... then the air pressure behind the bb does the work..
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