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How To Calculate The FT/LB Of Your Airgun.


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#1 robbobsam

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Posted 16 February 2010 - 09:38 PM

To calculate the Ft/lb of an air rifle you do the following calculation.

ft/lb = Velocity of pellet (feet per second) x Velocity of pellet (feet per second) x Weight Of Pellet (Grains) / 450240

eg, 712ft per second x 712ft per second x 10.6 grain pellet weight, divided by 450240 = 11.93ft/lb

712 x 712 x 10.6 / 450240 = 11.93ft/lb

Simple !!!

#2 mickmep

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Posted 16 February 2010 - 10:15 PM

or even easier................buy a combro for around 40. :hmm:
in my opinion a must have if you have a non fac air rifle.

bought my rapid second hand and it was doing nearly 14 ft-lb when i checked it.
probably not much chance of having it checked by police, but would hate to think what would have
happened if it was while it was at illegal power.
the fact that it was bought like it would be no excuse, and to be honest for 2 ft-lb not worth the risk.

#3 mart46

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Posted 17 February 2010 - 11:36 AM

or even easier................buy a combro for around 40.
in my opinion a must have if you have a non fac air rifle.


I can second this - had a new spring fitted in my hw97 by a shop and when I got it home, it was doing nearly 15lb-ft !! Did have words with the shop owner when I returned it!!

#4 Al Downie

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Posted 17 February 2010 - 12:14 PM

Can you enter the pellet weight into a Combro??? I've had one for a few months and been measuring fps and then faffing about with my calculator! What a doofus. RTFM!

#5 mickmep

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Posted 17 February 2010 - 01:49 PM

Can you enter the pellet weight into a Combro??? I've had one for a few months and been measuring fps and then faffing about with my calculator! What a doofus. RTFM!


you can with the mk4, cant comment on the earlier ones.
after you've shot through it you can read fps or ft-lb for the shot.

if you have a mk4 you hold the top button (reset) for about 14 seconds and then can set pellet weight and a few other things.

#6 SirFox

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Posted 17 February 2010 - 01:51 PM

Don't they make those small chronographs?

#7 mickmep

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Posted 17 February 2010 - 02:31 PM

Don't they make those small chronographs?


yep.
small plastic ones you just fit to the ned of the barrel.
not suitable for rimfire, but ok for fac air rifle.

they are a great bit of kit, can buy direct from combro for 40.
worth it for the peace of mind, knowing you air rifle is not generating illegal power, and knowing
it is running near the legal limit, use mine regularly to keep an eye on the airgun.

#8 Dekers

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Posted 21 February 2010 - 06:34 PM

you can with the mk4, cant comment on the earlier ones.
after you've shot through it you can read fps or ft-lb for the shot.

if you have a mk4 you hold the top button (reset) for about 14 seconds and then can set pellet weight and a few other things.


My Crombo is about 10 years old and you can on that!




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