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Post by trackman800 on Aug 8, 2012 18:54:54 GMT -5
knief
If you could send it to me id appreciate it. We will make the changes immediately. I would assume that since the same amount of psi is being applied to the .2 bb (and yes i know there is more inertia with .4s) that when they were moving through the chrono at 395 we had to be pretty darn close.
If there is a miscalculation we certainly will keep it at 288 for now on.
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Post by Knief on Aug 8, 2012 19:45:16 GMT -5
It's simple Newtonian physics. You can calculate it yourself using the equation KE=.5m*v^2 and some simple unit conversions. However, it's far easier to just use Arnie's FPS calculating tool, which does all the math for you: arniesairsoft.co.uk/?filnavn=/articles/fps_limits/fps_calc.htmPlug in .20g bbs and 410 FPS and you get an output of 1.55J. Then move down the page and plug in 1.55J and .40g bbs and you get an output of 288 FPS. I don't pretend to know a lot about P*s, but as I understand it, they do some funky things at the chrono when you change bb weights. I know that Lion Claws chronos based on the bb you're using and calculates muzzle energy. That's really what we should do with all guns on the field, but its far too cumbersome. Since regular AEGs don't change muzzle energy significantly when you change bb weight, it make sense to chrono them with .20s. Since P*s allegedly do, it seems that the best solution is to use the bb weight that the player is going to use. I'll work up a quick chart to tell you what you should be chronoing to hit each FPS/MED limit with every possible bb weight.
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Post by trackman800 on Aug 8, 2012 19:56:40 GMT -5
At lions claw we got in with the same identical settings but id rather be not make people angry with polar stars. We only run. 40s so if 288 fps is it i will use it for now on. Not 295 to 300 like we are currently.
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Post by Tank on Aug 8, 2012 20:15:50 GMT -5
Lion Claws allows higher FPS than MiA. They did chrono with .25 we chrono at .20. If you take our .20 FPS and figure what it would be at .25, it would be less than what they indicated for .25.
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Post by Knief on Aug 8, 2012 20:24:04 GMT -5
I highlighted some common bb weights. Yellow for 6mm bbs, blue for 8mm.
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Post by trackman800 on Aug 8, 2012 20:31:34 GMT -5
288 it is. We will have the change made for this sunday at no limits.
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Post by Gimpalong on Aug 8, 2012 20:34:30 GMT -5
I don't pretend to know a lot about P*s, but as I understand it, they do some funky things at the chrono when you change bb weights. I know that Lion Claws chronos based on the bb you're using and calculates muzzle energy. That's really what we should do with all guns on the field, but its far too cumbersome. Since regular AEGs don't change muzzle energy significantly when you change bb weight, it make sense to chrono them with .20s. Since P*s allegedly do, it seems that the best solution is to use the bb weight that the player is going to use. I'll work up a quick chart to tell you what you should be chronoing to hit each FPS/MED limit with every possible bb weight. Knief is basically spot on. The prescription of checking BOTH energy output and FPS is entirely correct and SHOULD be common practice. Will it become common practice? Probably not. All guns change muzzle energy when BB weight is changed. In general, a heavier weight bb will result in a higher energy output. So, for example, if a gun chronos at 400 fps with a .20 (roughly 1.5 joules), its energy output will "creep" upward as bb weight increases. So if a gun chronos at 400 fps with .20s (1.5 joules) and a .40 is dropped into the system, the fps will decline, but it is likely that energy output (joules) will increase past the 1.5 joule maximum limit. This doesn't always occur due to a variety of technical factors, but this is what people mean when they generalize about "energy creep." This phenomenon is platform independent, meaning it happens to varying degrees with AEGs, GBBR and P*s. How the gun is set-up as far as barrel length, cylinder volume, etc all factor in. A lot has been written about P* users being able to adjust the DP (poppet dwell) setting on their rifles to effectively "cheat" the chrono by over-voluming their barrels. The theory goes that the P* user can chrono with a .20 @ 400 fps (1.5 joules) and then will exceed that energy when they switch to a .30 or .40 as a result of changes in the DP setting which effects the amount of air being put out by the system. While it is true that energy output will increase as bb weigh increases, it is due to "energy creep" as explained above; it has not been shown to do with changes to the DP setting. The following quote is from Angus (Kurtis Hardy) on the Pstartalk forum. He demonstrates that while energy creep does occur it is not a result of changes in the DP (poppet dwell) setting. Below is a "chart" I created (and which can be improved on) which shows appropriate velocities along with energy output.* Sites with 400 fps (1.5 joule) with .20 maximum velocity limit: Maximum FPS for someone chronoing with .40s = 285 fps (1.5 joule) Maximum FPS for someone chronoing with .35s = 305 fps (1.5 joule) Maximum FPS for someone chronoing with .30s = 329 fps (1.5 joule) Maximum FPS for someone chronoing with .25s = 360 fps (1.5 joule) Maximum FPS for someone chronoing with .20s = 400 fps (1.5 joule) Sites with 330 fps (1.01 joule) with .20 maximum velocity limit: Maximum FPS for someone chronoing with .40s = 234 fps (1.01 joule) Maximum FPS for someone chronoing with .35s = 250 fps (1.01 joule) Maximum FPS for someone chronoing with .30s = 270 fps (1.01 joule) Maximum FPS for someone chronoing with .25s = 295 fps (1.01 joule) Maximum FPS for someone chronoing with .20s = 330 fps (1.01 joule) *Created using the energy/FPS calculator on Arnie's Airsoft. In concluding, I just want to point out that I'm not a tech. expert nor an expert with P*s. Please feel free to correct what I've written or my maths if something is awry. This is all based on stuff I've picked up by reading various forums. Cheers,
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Post by Knief on Aug 8, 2012 20:45:26 GMT -5
Yeah, I'm aware of the energy creep, though as I understand it, it's less significant with traditionl AEGs and PTWs. When I get the chance, I'm going to set up my chrono and run some tests of my own. Those jumps on Angus's chart are a hell of a lot greater than what I've experienced in the past with my PTW. Sadly, the heaviest bb I own is a .30. If anybody wants to ship me a hand full of .40s, I'd gladly add them to the mix.
Guns that run on pressurized gas have some different properties than those run on a spring and piston system. The most notable example that I can cite is WA SVIs. Changing the barrel from 5" to ~6.5" raises the velocity from about 330 FPS to 400FPS. Doing the same in an AEG does essentially nothing. I wouldn't be surprised if bb weight plays a larger role in determining muzzle velocity of the system in a P* because of a similar cause.
In either case, the results that Angus posted are telling about chronoing at least P*s, if not all AEGs in general. If that creep is higher, as I suspect, then we definitely need to chrono P*s with the weight bb that the user plans on using. If that creep is similar in all AEGs, then we should do the same with all AEGs. There's a big difference between 1.49J and 1.92J. In .20g bb terms, that's the difference between 400 FPS and 454 FPS. If our limit is 400, I don't want somebody taking a 450 FPS equivalent gun onto the field with full auto and a 20 foot engagement limit.
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Post by specks159 on Aug 9, 2012 1:37:37 GMT -5
The energy creep depends on the setup of the gun. It is more pronounced with the P* than it is with AEG's. The reason is due to the fact that many P* systems are highly overvolumed, while AEG's have their cylinder to volume ratio closely matched. A .2g bb has a lower inertia than a .4g bb. The .2g bb will accelerate faster than the .4g bb due to its lower inertia. In an AEG, the .4g bb will stop accelerating within the barrel as the air behind it runs out of pressure. The result is a similar power output to the same AEG firing .2g bbs. Now in a P* setup, there is usually plenty of excess air behind the bb, allowing the .4g bb to accelerate until it leaves the barrel, thus producing a higher power output than would be produced when the gun is shooting .2g bbs.
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Post by Gimpalong on Aug 9, 2012 5:02:30 GMT -5
It also doesn't help that the common advice passed around in P* circles is that you "should use the heaviest BB available to you." As a result, a lot of people chrono with .20s, are under the field limits, load their magazines with .40s and take the field with guns shooting well over the joule limit.
On the field, they experience much better range as a result of the higher level of energy they are outputting and so, naturally, because extra range is good, the "you should use the heaviest bbs available to you" line (which results in "cheating" the chrono) get passed on and on and has gradually developed into common practice.
That said, there's nothing wrong with using heavy bbs, users just shouldn't be using them to (either intentionally or unintentionally) to "cheat" the chrono.
As Knief said, chrono P* users with the BBs they plan to use, check FPS and energy output and tag the gun's receiver with the at chrono PSI.
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Post by trackman800 on Aug 9, 2012 9:35:56 GMT -5
As p* users we should print off an FPS chart similar to the one posted above and keep it in your gun case. I don't believe field mods should have to memorize a thousand different BB weights and there effective Joules.
I plan to carry the chart with us so that we can chrono with the actual BBs we are using. It seem this will be the most effective way of limiting any on field issues.
If anybody knows where i can buy 4 field locks please post the link on the forum so that p* users can look into that also.
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Carter
New Member
GK5
Posts: 76
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Post by Carter on Aug 9, 2012 10:06:52 GMT -5
As p* users we should print off an FPS chart similar to the one posted above and keep it in your gun case. I don't believe field mods should have to memorize a thousand different BB weights and there effective Joules. I plan to carry the chart with us so that we can chrono with the actual BBs we are using. It seem this will be the most effective way of limiting any on field issues. If anybody knows where i can buy 4 field locks please post the link on the forum so that p* users can look into that also. www.tnkguns.com/Airsoft-Parts-and-Accessories.html
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Post by Knief on Aug 9, 2012 12:43:05 GMT -5
Trackman,
I put this chart together using MiA standards, but it's really simple to add in different Joule limits. If you want I could add in LC limits and basic 400, 450, 500, 550 limits, or whatever else you wanted.
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Post by X on Aug 9, 2012 15:09:10 GMT -5
The energy creep depends on the setup of the gun. It is more pronounced with the P* than it is with AEG's. The reason is due to the fact that many P* systems are highly overvolumed, while AEG's have their cylinder to volume ratio closely matched. A .2g bb has a lower inertia than a .4g bb. The .2g bb will accelerate faster than the .4g bb due to its lower inertia. In an AEG, the .4g bb will stop accelerating within the barrel as the air behind it runs out of pressure. The result is a similar power output to the same AEG firing .2g bbs. Now in a P* setup, there is usually plenty of excess air behind the bb, allowing the .4g bb to accelerate until it leaves the barrel, thus producing a higher power output than would be produced when the gun is shooting .2g bbs. Specks is spot on here. With an AEG the amount of air is always limited to the size of the cylinder. On a P* the volume is essentially unlimited. AEGs experience creep due to the fact that the heavier BB is accelerating for a longer period of time. P*s experience this AND are able to maintain pressure all the way to the end of the barrel. AEGs will lose pressure as the BB gets closer to the end of the barrel (same amount of air in a bigger space). Thus the P*s creep is more pronounced. How hard would it be to give the chrono operator a calculator and Joule limits? After the first 10 times I'm sure he would be pretty fast at it. The chart works too, I'm just throwing out another option in case the host doesn't have the chart handy.
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Post by Knief on Aug 9, 2012 15:27:57 GMT -5
He'd have to have a calculator, unit conversion table, and the formula for determining KE. Seems like tucking a chart in your chrono box would be easier.
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