Chronograph Best At The Moment

[Gambo]

FPE Formula is Pellet weight (gr) x FPS x FPS divided by 450240 or 450436.7

I've never heard about dividing by 450436.7 before......can you elaborate please Travis? Thanks.


I have been using a Skan for years, it's been superb.

[angrybear]

I've never heard about dividing by 450436.7 before......can you elaborate please Travis? Thanks.


I have been using a Skan for years, it's been superb.

How about dividing by 450800 ???
this is from the Helston Forensics Standard Airgun test;

[ballisticboy]

How about dividing by 450800 ???
this is from the Helston Forensics Standard Airgun test;

The "formula" at the top of the page is completely wrong, it is 2 x G, not G squared. They have also used an old incorrect value for G. The calculation has used G + G which is not G squared and the way it is written would not give the answer they have if the calculation is carried out in the correct order. Also, grams and grains are measures of mass not weight, so basically whoever wrote that "formula" or carried out the calculation is mathematically ignorant. Unfortunately, only too common of people in the commercial forensic laboratories based on the evidence I saw when working.

The value 450436.7 comes when the internationally correct accepted value for acceleration due to gravity is used.

[Travis299]

I've never heard about dividing by 450436.7 before......can you elaborate please Travis? Thanks.


I have been using a Skan for years, it's been superb.

450240 is 2 x velocity of gravity x 7000, (2 x 32.16 x 7000 = 450240)
450436.7 is 2 x velocity of gravity x 7000, (2 x 32.17405 x 7000 = 450436.7)
The constant 450240 or 450436.7 depends on which value you use for the velocity of gravity.
32.16 ft/s/s or 32.17405 ft/s/s. There are 7000 grains in one pound.
The difference does not matter which ever constant is used for the FPE calculation.

[Gambo]

Thanks for the reply Travis.

[Shed tuner]

450240 is 2 x velocity of gravity x 7000, (2 x 32.16 x 7000 = 450240)
450436.7 is 2 x velocity of gravity x 7000, (2 x 32.17405 x 7000 = 450436.7)
The constant 450240 or 450436.7 depends on which value you use for the velocity of gravity.
32.16 ft/s/s or 32.17405 ft/s/s. There are 7000 grains in one pound.
The difference does not matter which ever constant is used for the FPE calculation.

good info, I'd only ever seen the 450240 figure before.

The difference between that and the 450437 is around 0.04% though, so not really relevant and certainly less significant that a one fps chrono error...

[ballisticboy]

450240 is 2 x velocity of gravity x 7000, (2 x 32.16 x 7000 = 450240)
450436.7 is 2 x velocity of gravity x 7000, (2 x 32.17405 x 7000 = 450436.7)
The constant 450240 or 450436.7 depends on which value you use for the velocity of gravity.
32.16 ft/s/s or 32.17405 ft/s/s. There are 7000 grains in one pound.
The difference does not matter which ever constant is used for the FPE calculation.

It is not a "velocity of gravity" it is the acceleration due to gravity. As I said before, the second value 32.17405 is the ft/s/s value of the internationally accepted value for the acceleration due to gravity, which is actually 9.80665 metres per second squared.