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Do you think getting shot with lighter BBs from an an upgraded gun would hurt more, less, or the same?

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Old November 4th, 2008, 05:30   #31
MadMax
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In a nutshell that's kind of correct. However I don't think the pressure really build up so much as reach an equilibrium when the pellet gets moving. Initially almost all of the pressure drop is at the valves and orifices because the pressure on the other side of the mag valve is atmospheric pressure so the initial flow rate has almost all of the pressure drop right at the mag valve.

At some point pressure builds up and gets the pellet to pop past the hopup and start down the barrel.

The pressure drops I'm describing are not due to leaks so much as actual flow resistance. For instance if you crack open a valve on your BBQ tank a 115psi pressure drop occurs across the valve itself between the inside of the tank and the environment. Flow through the valve accelerates until all of the pressure drop occurs over the valve and you have a flow rate which drives a 115psi pressure drop over the valve resistance.

Imagine applying 30psi to one of a water hose to drive the water. At one end you've got 30psi. At the open end you've got 0psi (atmospheric) so you end up driving water as fast as 30psi can deliver over the entire flow resistance of the hose. No side leaks, just the flow resistance of the hose which delivers a certain flow rate of fluid for a given pressure drop.
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Old November 4th, 2008, 05:31   #32
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Hahaha great minds think alike, I just edited with the water hose visual too. LOL
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Old November 4th, 2008, 10:59   #33
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There's an easy way to settle this. Start a bizarre internet myth so the Mythbusters test it.

Call it the Savage Cheek (pick wehever one) Test for APP (airsoft projectile pain) factor.
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Old November 4th, 2008, 11:02   #34
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Quote:
Originally Posted by mcguyver View Post
[the majority of airsoft] Guns are too inconsistant to apply a simple formula and expect to get the right answer all the time. Sometimes it works, but that's luck.
^ truth

Actually, there are a number of correct things posted in this thread...and a little misinterpretation by some of what others are trying to put forward.

I ran a bunch of velocity tests when setting up a buddy's rifle for both CQB and outdoors with a single mechbox (I found playing with the barrel length far more interesting than fiddling with other variables).

It was boring and I'm not convinced of the results. Despite efforts to keep the tests practical and consistent...there are a lot of variables that come into play. I might repeat the tests again this winter if I get really bored...but I'd have to be really, really bored and it's basically a waste of money and time.

It sounds great and simple to say..."When you switch between 0.20g and 0.25g bbs, you'll drop 30fps"...but there's such a variance that even 10fps on a 400fps rifle is just 2.5% of the overall velocity and so pretty inconsequential given the system...and anyone who has tried to do these types of tests knows how easy a 10fps spread pops up. With a lot of data you can start to see trends...but what to do with the spread/%error? The comment becomes..."when you switch from 0.20g to 0.25g bbs, you'll get a 20-40fps drop" and starts to become useless as a guide line.

Extend this to encompass the fact that one airsoft gun's compression and setup can vary wildly when compared to another...and it's a very rough guideline at best. (I.e. take Stalker's uber +/- 1fps target grade bolt action and extend the results to a Kraken)

What is valid...is for each person to try out different BB weights and then to say..."In MY setup, going from 0.XXg to 0.YYg resulted in drop/increase from ABCfps to XYZfps". Unfortunately those results are limited to your rifle...and lose validity for another.

So far as GBB's...heavier bbs work better. With all the "target"/IPSC/CAPS shooting lately...it's painfully evident that when you want to shoot better than MOB (Minute of Body), and you want to shoot a consistent sub-palm size cluster...you shoot heavier BBs. Zero controlled tests to back this up...just practical observations. So far as what weight hits harder...that's easy to see after a night at the range...heavier BBs punch though the patched up metric targets better than the 0.20g lightweights that are often stopped/stuck in the target cardboard. ***edit*** but obviously simply switching to heavier BBs won't make an inaccurate GBB shoot like a tack driver***

To address the original question...heavier bbs hit harder than lighter BB in normal field/engagement ranges. I know this because I've been shot a lot. I also know that you should load 40mm grenades with lighter BBs...because they sting like a MoFo when you get blasted up close.

Last edited by m102404; November 4th, 2008 at 11:05..
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Old November 4th, 2008, 11:15   #35
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ahah yes recently I was testing with a shit chrony and at one point I got 700 fps.
That has to be an error
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Old November 4th, 2008, 11:42   #36
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in joules

0.2g@350=1138
0.2g@380=1340
0.2g@410=1561

0.3g@350=1707
0.3g@380=2011
0.3g@410=2342

So (unless my calculations are crappy crapola) if switching to 0.3 makes you lose roughly 30 fps, you will still gain from 300 to 500 joules at these speeds (including speed decrease), while a 30 fps increase at constant weight will only add 200 joules at 0.2g and 300 joules at 0.3g.
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Old November 4th, 2008, 11:55   #37
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Uh Jimski, I hope airsoft pellets don't carry that kind of energy. Try going down about 3 powers of 10.
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Old November 4th, 2008, 11:58   #38
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Quote:
Originally Posted by Jimski View Post
in joules

0.2g@350=1138
0.2g@380=1340
0.2g@410=1561

0.3g@350=1707
0.3g@380=2011
0.3g@410=2342

So (unless my calculations are crappy crapola) if switching to 0.3 makes you lose roughly 30 fps, you will still gain from 300 to 500 joules at these speeds (including speed decrease), while a 30 fps increase at constant weight will only add 200 joules at 0.2g and 300 joules at 0.3g.
Check your units. You're off by a factor of 1000 (convert grams to kg???)

MadMax,

Have you seen this before: http://cybersloth.org/airsoft/trajectory/index.htm

I'm curious to get your take on it coming from another engineer.
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Old November 4th, 2008, 12:06   #39
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Quote:
Originally Posted by Flatlander View Post
Check your units. You're off by a factor of 1000 (convert grams to kg???)

MadMax,

Have you seen this before: http://cybersloth.org/airsoft/trajectory/index.htm

I'm curious to get your take on it coming from another engineer.
That's one of the source we used to build our sniper ballistic charts and set our standards. I'v studied the whole thing and it's very good IMO.
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Old November 4th, 2008, 12:17   #40
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Fox, I'm not trying to be condesending but were you able to understand and validate all of his theory? (because that's all I saw was theory and no empirical evidence he claims he has to support his theory). With the theory he covers you more than likely need an engineering degree to understand it; highschool physics won't suffice!

EDIT:

It's been a bit since I browsed through it but a few things I thought were off were:

- His coef of drag on a sphere: I think his theory was wrong IIRC
- IIRC he claims that the BB's will all hit their target in the same time amount reguardless of weight; seems counter intuitive to me.
- As I mentioned, the lack of imperical evidence to backup his theory which he claims he has and are damn near spot on.
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Old November 4th, 2008, 12:32   #41
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Quote:
Originally Posted by Flatlander View Post
Check your units. You're off by a factor of 1000 (convert grams to kg???)
ah yes I used grams
weird I thought the equation used m.s-1 and grams
crap wiki says it's kg
huhu
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Old November 4th, 2008, 12:34   #42
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.28's hurt like a son of a bitch compared to .20's.
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Old November 4th, 2008, 15:43   #43
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Quote:
Originally Posted by Flatlander View Post
Fox, I'm not trying to be condesending but were you able to understand and validate all of his theory? (because that's all I saw was theory and no empirical evidence he claims he has to support his theory). With the theory he covers you more than likely need an engineering degree to understand it; highschool physics won't suffice!

EDIT:

It's been a bit since I browsed through it but a few things I thought were off were:

- His coef of drag on a sphere: I think his theory was wrong IIRC
- IIRC he claims that the BB's will all hit their target in the same time amount reguardless of weight; seems counter intuitive to me.
- As I mentioned, the lack of imperical evidence to backup his theory which he claims he has and are damn near spot on.
Based on my experience, what he demonstrated by his theory and backed by his testing In real life, is a good base to start from.

You want emperical study, go ahead, make your own study. But as far as I know, his study is the only one in existance that is complete and to the point. It may be an unproven theory, but that does not make it a bad one.

If you took the time, like me, to read ALL that stuff and pull out the valued and make your own calculations, you will know that this stuff is usefull to us and it can be applyed to the game.

Since the BBs and gun are inconcistant, thoses values are ment to be used as a base line.

ex: I made range card to be used with X weight of BBs at X fps. It also has mildots indications. I know for a fact that the mildots indication on my range cards won't result in a one shot one hit, but I know that it's a good estimation on where to start to acheive a one shot, closer to one hit than a blind shot... See what I mean?

As for the joules indications, it's the first time I see charts that take into account BB terminal velocities, air dencity, energy, range.... So for setting MED (Minimum engagement Distances), I think it's the best thing we have to work with.

I don't need a physic Ph.D to use these thing. I might not be able to fully understand his calculations and do my own to validate, but I know how to interprete the values and apply the theory on my experience.
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Old November 4th, 2008, 16:11   #44
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Why not just get a chrony that can rate joules... and fire through it with the same gun at different distances with .2 and .3?

see which one retains more energy
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Old November 4th, 2008, 16:29   #45
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Quote:
Originally Posted by Amos View Post
Why not just get a chrony that can rate joules... and fire through it with the same gun at different distances with .2 and .3?

see which one retains more energy
Because it probably would not be an accurate test. It would shed some light on the relationship between exit velocities and BB weight, but the question here I understand is measuring impact energy. Some kind of test using a kind of ballistics gel with ranged tests would probably be more a long the lines of getting the answer people want. A .20gr bb will have retain more of its energy for a far greater time than say a .42gr, weight and back spin can compensate for cross-wind interference but ultimately the added weight slows down the BB dramatically when using the same power to launch the .20gr BB.

The problem I saw with Jimski's numbers before the answers, was that he guaged a .20gr compared to a .30gr with both having the same FPS. Now for what we are looking for, that is completely off the mark on the numbers. My bolt actions for instance would launch a .20 gr BB at 450fps while the .30gr would get aprox 350 out of the same energy. So the question starts to become is the reduction in speed countered by the increase of BB weight affect the outcome of overall impact strength. But I do not believe this stops simply at the exit velocity, because as I said, the heavier round will loose its speed faster than the lighter. This is why I'd think some sort of range test with a meter that can detect and measure the impact force; done at ranges of 20ft 40ft 80ft 100ft 150ft or along those lines would be more accurate to determine which is going to be "felt more".

The reason I really don't think that exit velocity is the real way to determine this is after some years I've noticed and have been talking to another local about the "Matrix effect." This is where after time you start to notice that you start tracking and instinctively start to "avoid" BB rounds as you see them coming at you. Now I'm not talking Super Neo on the rooftop here where you're over backwards cartwheeling your arms and so on. But you are able to start tracking the heavier rounds and as such it gives you a chance to avoid the round. Lighter rounds traveling faster become harder to see and as well harder to react in time at closer distances.
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