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Old December 2nd, 2009, 08:49   #1
youngguns
 
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BB's and Velocity

Is there a formula or something to tell you what FPS a bb will shoot with a different weighted bb when you crony at .20?

For example. Standard Crony is using .20. My gun shot 360 fps. What would it shoot using a .28?
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Old December 2nd, 2009, 09:30   #2
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Not really...but there's been a couple of threads on it. CDN_Stalker posted a bunch of stuff in a thread called "BBBastard...something, something...."

I did some testing last year as well...can't recall exactly, but I believe that it was along the lines of:
0.20->0.25 drop 30-40fps
0.20->0.28/0.30 drop 100fps

There's a gabizillion posts about how simply dropping FPS by increasing BB weight does not:
- make the rifle safe or under MAX field limits...FPS is measured/noted with 0.20g BB weights (i.e. if the limit is 350fps...and your rifle is shooting 360fps, simply using heavier BBs to shoot under is not fair)
- there may be some debate about this (don't know why)...but, IMO, lighter BBs do not hit as hard as heavier BBs at any practical range. FPS limits are established so that the risk of injury at close range is reasonable.

Hope that helps,

Tys
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Old December 2nd, 2009, 09:32   #3
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Well there are theoretical formulas, but they never work in real situations. The problem is, a BB can come out of the barrel with a certain muzzle energy with one type of BB (0.5*m*v^2). If you then used a heavier BB, it should theoretically be the exact same muzzle energy. However, heavier BBs tend to have a larger amount of energy imparted on them by the system, and will therefore come out with a higher muzzle energy.

Your best bet is to do the theoretical calculations ( (0.2)*(360)^2 = (0.28)*v^2 solve for v), and then assume that it is going to be a bit more than that.
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Old December 2nd, 2009, 09:34   #4
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When they Crony, they use a series of shots and then divide by the numbers shot which gives the FPS speed right? They dont just shoot one and that is the FPS do they?


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Originally Posted by m102404 View Post
Not really...but there's been a couple of threads on it. CDN_Stalker posted a bunch of stuff in a thread called "BBBastard...something, something...."

I did some testing last year as well...can't recall exactly, but I believe that it was along the lines of:
0.20->0.25 drop 30-40fps
0.20->0.28/0.30 drop 100fps

There's a gabizillion posts about how simply dropping FPS by increasing BB weight does not:
- make the rifle safe or under MAX field limits...FPS is measured/noted with 0.20g BB weights (i.e. if the limit is 350fps...and your rifle is shooting 360fps, simply using heavier BBs to shoot under is not fair)
- there may be some debate about this (don't know why)...but, IMO, lighter BBs do not hit as hard as heavier BBs at any practical range. FPS limits are established so that the risk of injury at close range is reasonable.

Hope that helps,

Tys
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Old December 2nd, 2009, 09:38   #5
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Using an online airsoft calculator it says that 360 fps with .2 bbs is 1.2 joules of energy.

At 1.2 joules a .28 bb should travel at 304 fps.

These figures are from the ASG calc V2.7

Hope this helps

http://asgcalc.hollved.com/us/
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Old December 2nd, 2009, 09:44   #6
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Great Software.

Thanks
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Old December 2nd, 2009, 10:02   #7
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Yeah...there's usually 5 or so shots taken. If the majority of the shots (i.e. 4/5) are under you're good to go.

Note: For gas pistols and rifles...the power stuff goes out of whack. With a heavier BB in a gas gun, the expanding gas behind it has more time to do it's thing and you'll end up with a higher Joule for a heavy BB than a faster lighter BB out of the same gun.

Theoretically AEG systems are constant...GBB can be variable. With a NPAS system the shift to redirect gas backwards only happens when the BB is out of the barrel...the longer it's in the barrel, the more gas is dumped down towards the muzzle. We're talking slivers of time here...but it does make a FPS/Joule difference.

Stick to the simple rule:
- use a real chrony...no lame pop-can tests
- use 0.20g BBs...if you're just using them to chrony with...a bag will go a long, long way and there's no question as to the result.
- at games/events where chrony-ing is strict...simply have a loader ready with 0.20's...have the player step up with a mag, fill with 8-12 0.20 BBs (that's about 2-3 plunges from the average loader) and then chrony.
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Old December 2nd, 2009, 10:21   #8
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That airsoft FPS calculator is accurate. My G&G 550 was shooting 350 fps/w .20s
I put a tightbore in it, and it went to 360fps/ .20s
Chronied at my last game with .28s and the FPS was 300 - 304 fps
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Old December 2nd, 2009, 10:47   #9
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http://www.airsoftcanada.com/showthr...hlight=bastard

http://www.airsoftcanada.com/showthr...hlight=bastard

Easiest way to find them is to search in the reviews section for bastard.

Most of the time a rough rule of thumb is best. Calculations and formulae are fine, and sometimes actually reflect reality, but actually trying weights and chronying is the best way. Factors like air density, etc. come into play at times.

Nutshell, as Tys pointed out, ~30fps drop between 0.20g and 0.25g BBs (I'm basing all this on BB Bastards BTW).

I also found there was little if any fps drop when going from 0.28g BBs to 0.30g Bastards, but interestingly, there was a ~20-30fps drop from Bastards to 0.30g SIIS BBs, weight wasn't the difference, Bastards are just bigger and more precise in size/shape.

And most of my testing has shown a ~100fps difference between 0.20g and 0.36g BBs.

So those are the 'rules of thumb' I go with daily.
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Old December 2nd, 2009, 13:11   #10
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There is a calculator and a lot of information at my website at:

http://www.bbbastard.com/index.php?o...d=54&Itemid=59

and the calculator at

http://www.bbbastard.com/index.php?o...d=53&Itemid=57
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Old December 2nd, 2009, 13:28   #11
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would there be any interest in a VBscript FPS calculator? I need to make some random program for school and I am thinking of either doing this or recreating my D&D character generator.
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Old December 2nd, 2009, 13:34   #12
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Quote:
Originally Posted by Bissa View Post
would there be any interest in a VBscript FPS calculator? I need to make some random program for school and I am thinking of either doing this or recreating my D&D character generator.
Thats already on my site - its javascript, but its there. See the second line.
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Old December 2nd, 2009, 13:37   #13
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damn, beat me to it. and that is impressive.
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Sergeant Gerry Boyle: I don't want to see it. Babies all look the same. The only time a baby doesn't look like every other baby is when it's a really ugly baby. So, unless it's a photo of a really ugly baby, I don't want to see it.
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Old December 2nd, 2009, 14:29   #14
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It's been there for a few months now LOL. I guess we need to get some better promo going on that site.

It's called the MSED Calculator (Minimum Safe Engagement Distance -from the online Airsoft Trajectory Project), but it shows lots of other parameters, and the science is also posted if you have questions on how the calculator works in the background.
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Last edited by Blackthorne; December 2nd, 2009 at 14:37..
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Old December 2nd, 2009, 14:44   #15
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oh I understand exactly how it works in the background. I know physics to first or second year university level for momentum and stuff like that. I have already written an FPS calculator on my TI84+ I was just wondering if people were interested in a standalone program that can be run without internet access to do basically all the math there.
I think the TI84+ version would be useful for a person doing cronies so they can convert current velocity at the field in a couple seconds and not have to type in the equation every time.
and as for the program being there for several months, since I am still not AVed I don't get out to many games. and I am in BC where we don't really deal with BBbastard as much, so I don't go to his site too often and so I didn't see that till he pointed it out.
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