Curious about the way they speed check one's WFTF rifle at major FT matches.Currently I have set up my HW97K for WFTF. I am shooting JSB Exacts 8.44 grain pellets at 799 fps average (11.96 FPE)Sometimes it goes up to 807 fps (12.2 FPE) on one or two shots out of five.What is the margin of tolerance do they allow for speed when determining FPE?Is it shot over the limit and you are disqualified?I am thinking of just entering Open Class to be on the safe side if certain venues and days where the rifle is shooting faster than 800 fps.-LeoI have not attended any major venues yet. But plan on at least going to the Crosman event in upstate NY and the Pyramyd Air Cup. Maybe the Nationals.
...As you can see clearly, the 2% variation is in the VELOCITY. Now, I do not know where Scott gets the 816 fps for an 8.44 grs. pellt, he must be using a different gravity value. Since California is a different Repubic, he may live near the galactic reactron where gravity is somewhat whimsical. For the rest of us mortals, AAFTA selected a constant to transform weight into mass that takes into account a standard gravity and that constant is 450436....
...What is the margin of tolerance do they allow for speed when determining FPE?Is it shot over the limit and you are disqualified?...
Thanks for the information. Currently I have one shim installed in the Vortek kit with Krytox grease to get 800 fps average with JSB exacts. I am hoping over time the velocity would drop as I continue to shoot it more.Is it realistic that the Vortek spring will weaken over time to get a lower velocity and be WFTF compliant?
Quote from: HectorMedina on March 13, 2016, 10:24:47 PM...As you can see clearly, the 2% variation is in the VELOCITY. Now, I do not know where Scott gets the 816 fps for an 8.44 grs. pellt, he must be using a different gravity value. Since California is a different Repubic, he may live near the galactic reactron where gravity is somewhat whimsical. For the rest of us mortals, AAFTA selected a constant to transform weight into mass that takes into account a standard gravity and that constant is 450436....Hector,Gravity has nothing to do with it.As you stated:Energy(ft-lb) = Mass(grains) * Square[ Muzzle Velocity(fps) ]450436Therefore:12fpe=8.44gr * Square[800.27fps]/450436andVelocity = square-root[12 * 450436/8.44] = 800.27fps800fps x 102% = 816fpsSo if Leo always reads under 816fps using an 8.44gr pellet, it passes according to AAFTA rules.I'm not saying that is a prudent velocity to tune for. Leo asked how they checked guns. The only "major" matches he listed in his plans were USA matches. So those are the rules (AAFTA WFTF Division) I used as the basis for my answer.
Scott,Just a joke.BUT, gravity has ALL to do with it. Without a value of gravity the constant 450436 (or any other you want to choose) has no meaning. Without gravity you are using weight (force-grains) instead of a mass (slug).Anyway. Sorry if my joke was not funny.Héctor
Quote from: HectorMedina on March 14, 2016, 10:30:35 PMScott,Just a joke.BUT, gravity has ALL to do with it. Without a value of gravity the constant 450436 (or any other you want to choose) has no meaning. Without gravity you are using weight (force-grains) instead of a mass (slug).Anyway. Sorry if my joke was not funny.Héctor"Without a value of gravity the constant 450436 (or any other you want to choose) has no meaning."The jokes are a good segue to educate those that still believe in a relationship between gravity and kinetic energy. So thanks Hector.For those interested, if you don't know the joke: 450436 is a result of unit conversion in the formula: KE = 1/2mV^2The mass of a pellet is usually given in grains. The unit of mass that we need for KE in the imperial system is slugs.1 grain = slugs/225218https://www.google.com/search?q=slug+grainWhen we substitute grains for slugs, in the KE formula, we get:KE = 1/2 * ?gr/225218 fps * fps = grains * v^2/450436That is where the 450436 comes from. It's the same on earth. moon, mars, or in deep space. Gravity plays no part.450436 is the correct denominator when calculating the FPE of grain projectiles. So don't believe someone if they say it depends on where you live on earth - because they either don't know any better, or they are making a joke.
Being simple minded I just use this...........http://airguns.net/calculators.phpAnywhoo.....me thinks that airgunners get too hung up on the minutia of "numbers" that often have little bearing on accuracy or performance since the projectile itself (those lead badminton birdies called pellets) aren't very consistent after weighing and measuring thousands of even "top brand" pellets.LOL....even IF everything were "perfect" for one shooting session, this "perfection" is easily upset by uncontrollable things the next shooting session like atmospheric conditions.
Quote from: nced on March 15, 2016, 09:47:47 AMBeing simple minded I just use this...........http://airguns.net/calculators.phpAnywhoo.....me thinks that airgunners get too hung up on the minutia of "numbers" that often have little bearing on accuracy or performance since the projectile itself (those lead badminton birdies called pellets) aren't very consistent after weighing and measuring thousands of even "top brand" pellets.LOL....even IF everything were "perfect" for one shooting session, this "perfection" is easily upset by uncontrollable things the next shooting session like atmospheric conditions.Ed,You can use that calculator and it will get you close enough. The underlying constants are slightly off however. They probably used gravity in the equation (a poor method), and chose the wrong value of gravity. If gravity is used, it has to be "Standard Gravity". That's why the answers that they get will be off in about the third decimal place.The reason that some still do it that way is because someone used outdated science in the past and never bothered to correct it. You will see other justifications for using a denominator of 450,240. Those arguments are easily refuted.450436 is correct.450240 is very close, but wrong.
Man, metric world is a lot simpler. If you insert the SI units for weigth (kg) and velocity (m/s) into the formula (KE = 1/2mV^2), you get the resulting Joules directly. No strange multipliers needed.Example:JSB Exact 0.547g = 0.000547 kgMv 240 m/sKE = 1/2mV^2 = 0.5 x 0.000547 x (240)^2 = 15.8JOh.... and concerning the energy limit. Take into account the higher velocities on warmer days. On colder days like in this season it is safe not to tune much above 11 fpe. In summer it will go to 11.5-12 fpe. There is a 6 m/s difference with my 97k between a 5C and a 25C day.