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Old 3rd October 2013, 10:10 AM
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Brian.Samson Brian.Samson is offline
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Member of: Pontefract, Doncaster Airgun Range
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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.
I'll come up with some answers for you at lunchtime K.. but just quickly, we don't agree with the first bit.. 40fps downrange can (we think) in theory still hit the same POI. But.. it would depend on the velocity it started at (which we don't know)

Secondly, the lapua example.. The smaller the variation in MV as a percentage of the total velocity will have less effect.

So, for example, if you're getting a 50fps variation against a velocity of say 780 fps, the difference in POI will be much greater than if you're getting a 50fps variation against a velocity of 2000 fps. How much difference it makes would need to be calculated, but it might not be huge. Dunno?..

Anyhoo.. I'll see if I can come up with a sensible answer for the 40fps hitting the same level later on. If I had to put money on it though, I think the answer will be - either Si's reg is seriously foooked or he pulled the shot, or the chrono reading was wrong, or maybe there was some weird wind effect. Oh, or ballistics is wrong
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