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Old 3rd October 2013, 10:29 AM
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sven sven is offline
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Join Date: Dec 2009
Member of: FT Schalkhaar / SSV Ons Genoegen
Location: Arnhem, The Netherlands
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Originally Posted by kieran turner View Post
Just for the record and to throw another cat amongst the pigeons.

In theory 40fps variation down range would equate to massive POI changes and 40fps shot to shot variation would equate to massive POI changes, agreed?

Well how come then when admittedly this isn't air rifle related but still related to slinging lead down range. How come when using centre fire rifles (in this case 250gr .338 lapua) extreme spread over a 5 shot string was if memory serves me right around 50 fps ( chrono was approx 5ft from muzzle) yet the rifle(s) in question was still producing sub 1/2"MOA out to 800y and then around 1MOA at 1000y.

So in theory these rifles shouldn't of grouped as well as they did, somebody with far more intelligence explain that to me please.
The answer to this "high accuracy with high velocity spreads" problem might be: Positive Compensation.
It has been shown for .22 Long Rifle by Geoffrey Kolbe from Border Barrels. See this well written (but beware, it might cause headaches to some readers here ) article:

In short: Positive Compensation is caused by barrel vibrations in combination with a well tuned setup (i.e. a combo of stock/bedding/barrel and cartridge). And from what I understood (and I'm still only making my own mind up, so you might read something else yourself) it comes down to the fact that in a well tuned setup a slower bullet leaves the barrel when the vibrating barrel is pointing higher than when a faster bullet leaves the barrel. So the lower impact at target because of a lower velocity is compensated for by the higher pointing muzzle.
Field Target Schalkhaar:
Airgun Accuracy weblog:

Last edited by sven; 3rd October 2013 at 10:34 AM.
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