Acceptable FPS. Deviation

I think it is better to demonstrate it using your numbers, 875fps versus 850fps. a 25fps difference will result in:

approximately 1cm change of POI at 50m and 4cm change of POI at 100m
which is still not bad POI spread at all.

when i recalculate with 10fps difference, it will make 4.2mm difference ad 50m and 1.7cm at 100m.

these days many guns can do single digit and behold they still get bad bad fliers. 
basically it is NOT the shot to shot inconsistency is the main cause of fliers. there are more/different factors at play. dont aske me which LOL. many

G'day sirk,

I too have always wondered about the meaning standard deviation when checking some of my rifles and appreciate your explanation.

I have some rifles, mostly 10M rifles which give SDs under 10 as you wrote: "these days many guns can do single digit and behold they still get bad bad fliers." It seems many people consider 'fliers' to be occurring mainly due to pellet defects. As someone new to shooting air rifles I attribute all my fliers to my postural inconsistency, especially the initial shouldering arms and cheek-weld leading to inconsistency of sight picture. I know I am inconsistent.

That there are defective pellets is a given - one sees the odd deformed pellet in each batch of pellets, but how many pellets which look alright to the unaided human eye are really so defective that they, alone, cause fliers?

Jim

Via Ballarat
Australia

By the way, where is SK where you live?

SD of 10 is very high!
I am pleased when ES does not exceed 10.

I read a similar thread on this site last year regarding what an acceptable SD is (sorry, don't remember who wrote it. I do remember them mentioning Field target competition and shooting at 100plus yards accurately). I believe it was determined (by more experienced, knowledgeable members than I) that an ideal SD is 1% or less than your average velocity (6 fps or less for an average velocity of 600fps). This for maximum accuracy at distances greater than 40 yards, I think. The lower your SD, the tighter you can expect your groups to be at greater distances. In my limited experience, your SD makes little difference inside 30 yards, where most average shooters hunt and plink (unless of course your SD is totally, double digit ridiculous).