11th August 2013, 06:40 PM
Join Date: May 2009
Member of: Harriers FTC
Originally Posted by Brian.Samson
I decided to put the theory to the test yesterday and the results are quite interesting I think. I won't go into all the facts and figures because it would be a long post that most people probably wouldn't be too interested in reading.
Anyhoo... I have two batches of pellets that I use - some AA Fields and some Daystate Selects. The Selects are mega in my rifle. I also have the feeling that they don't seem to take as much wind either (difficult to prove, it's just my perception). The AA Fields I use also shoot very well (the best I've found apart from the Selects) and they also seem to group quite well at 55 yards - maybe not quite as good as the Selects, but not much difference between them as far as I can tell.
So... I thought I'd put my money where my mouth is and go out and do some downrange velocity tests with both batches of pellets and these are the results :
Both batches are pretty consistent over the chrono at the muzzle - average about 775-780 fps and a very consistent spread.
At 55 yards in a very light wind (practically nothing), 10 shots with the AA Fields gave a low of 567fps and a high of 597fps. The Selects did 605fps - 613fps.
That gave a range of Ballistic Coefficients of 0.0206 to 0.0243 for the AA's and 0.0255 to 0.0270 for the selects.
I think what most people use as a starting point average BC for 8.4's is around 0.022 / 0.023 which corresponds with my highs and lows with the AA Fields.
So to the calculations and theory... What that all means is that with the Fields, I should expect to see a variation in POI of 0.32 inch and a variation in a 5mph 90 degree wind of 0.6 inch - so the theoretical best group I could ever hope for with the Fields at 55 yards is about 1/2 and inch (I'd be happy with a 1/2 inch group at 55 yards)
The Selects however have a theoretical POI variation of just 0.07 inch and a variation in windage of 0.1 inch. So the theoretical best sized group I could put in with the Selects is practically pellet on pellet, certainly less than a 1/4 inch group at 55 yards!.
Now when it comes to testing pellets based purely on group sizes.. I'll be honest, I'm not a good enough shot to put in a pellet on pellet group at 55 yards with 10 shots, I'm not even good enough to consistently put in a 1/2 inch group.
I've had the odd group that I can cover with a 5p piece but it's not the norm. I'm basically more than happy if I can put in a group that I can cover with a £1 coin.
I think what I'm saying here is - I'm not a good enough shot to be able to reliably tell the difference between a good batch of pellets and a mega batch of pellets.
So from actual group sizes that I'm able to shoot - both sets of pellets seem to be about the same, I can potentially notice a slightly better group with the Selects, but I don't know how much of that is psychological or not.
But... the theoretical difference in wind drift is quite different!. Although the variation for a 5mph wind is 0.1 for the Selects and 0.6 for the Fields - the difference in wind allowance between the Fields and the Selects is about 3/4 inch.
So for two batches of pellets that both seem to group quite well (to the best of my abilities) I could potentially be gaining 3/4 inch drift by using the Selects instead of the Fields.
Now that's two batches that both seem to group well - if I'd compared a batch of pellets that didn't seem to group as well as my mega batch - the difference in windage could potentially be much more.
The conclusion - I think I've proved (to myself at least) that there can be quite a sizable difference in wind allowance between a two batches of pellets and also that downrange velocity testing is a far better method of testing pellets than just shooting groups.
I can't disprove your air stripper theory (because I don't have an air stripper on my TX) but I'd say that it's possible that an air stripper could not only improve group sizes but also reduce the amount of wind drift. But that's also true of selecting a good batch of pellets over a not so good batch of pellets - maybe potentially more of a difference than an air stripper would give you.
Interesting implications for using one batch for practice sessions and another for matches. Or even using selected pellets from a batch for matches.