Long range airgun shooting

[Terry D]

And Terry to go back to an earlier question, is there any defined pattern in your grouping, is it the vertical or horizontal measurement screwing up the sizes, or are they random. Tis the horizontal that always bigger when I'm giving this a go.

Horizontal mate, at least for the vast majority of the outdoors ones. The indoors ones were more circular. Has to be wind I guess.

After vowing never to drive myself bonkers again with this long range shooting lark, I'm actually itching to give it another go now.

No hope for some of us, really.

[Terry D]

… and what was the velocity, air temperature/pressure/elevation, pellet weight and the resulting BC value?

Hold on Dave, I'll just reach over and grab my weather station database readouts for those days......

Erm...I know we used weighed and selected Baraccuda Match in the 30 ft.lb. guns, and Ben kept all the data because he brought the picnic hamper and bottles of pop.

Hope this isn't too much ballistics for yuz.

[oldwun]

I think we should now shut the rest of the forum down, apart from the sales department that is used by the none profit making dealers/dabblers as there does not seem to be many posts any where else today.
Stirred up a small storm didn`t our now banned poster from down under, i have also noticed the odd couple of posts from the main objector to his posts being almost APOLOGETICK. For give my spelling/grammer but if the admin can use Gr8 i am certain a bit of thought will be considered before dragging me over the coals.

goodolddad

[Harry's Lad]

Hold on Dave, I'll just reach over and grab my weather station database readouts for those days......

Thanks. No worry, I'll wait ...

Erm...I know we used weighed and selected Baraccuda Match in the 30 ft.lb. guns, and Ben kept all the data because he brought the picnic hamper and bottles of pop.

So that was a H&N Barracuda Match in 0.177 was it? That would explain the differences. Poor BC even in 0.22 compared to JSB Exact, worse in 0.177.

“Apples and Oranges” as Gary C said …

Dave

[Harry's Lad]

I've just run the numbers through ChairGun(3) using the data available.

Harry’s JSB Exact:
0.22 JSB Exact (15.9 Grain), BC=0.037 (0.032 @ NTP = 0.037 @ 4000 Ft), MV= 874 Ft/s … 27 Ft-Lbf

Terry’s Barracuda: (I’ve made some assumptions here since Terry hasn’t supplied his velocity data)
0.22 Barracuda Match (21 Grain), BC ~ 0.024, MV= 803 Ft/s … 30 Ft-Lbf

From Graph:

• Energy equal @ 31 Yards = 22.5 Ft-Lbf
• At 100 Yards, JSB has 15 Ft-Lbf remaining, Barracuda has only 11.6 Ft-Lbf
• At 150 Yards, JSB has 11.2 remaining, Barracuda has only 7.3 Ft-Lbf
• JSB @ 12 Ft-Lbf ~ 139 Yards, Barracuda @ 12 Ft-Lbf ~ 98 Yards

I’ve uploaded the graph here

It’s all because of the BC difference. BC value is derived from exponential equations so that small differences (when the BC value is itself small) are significant. The increase in Harry’s BC value - by virtue of the 4000 Ft altitude – makes it even more so.
That is; 50% difference in BC (when the BC is only 0.03) leads to huge differences in downrange velocity/energy/POI whereas a 50% difference when the BC value is 0.5 is barely noticeable.

Again – because of the difference in BC value – Harry’s JSB would be a lot less affected by crosswinds …

This ballistics stuff is good, init?

Dave

[Terry D]

I've just run the numbers through ChairGun(3) using the data available.

I ran my .22 Baraccudas through a chrono'. Are you saying that ChairGun outranks that method, Dave?

Just curious, really.

[Sid]

The thing is, we don't know what conditions Harry was shooting under, apart from the 4,000ft elevation. Vaguely remembered from my flight training the density altitude ( which is what the pellet sees ) is derived from some other stuff like humidity and the pressure altitude ( rather than simply height above sea level )

I don't know how much difference this would make, but I personally would be inclined to trust TD's chrono, no offence Dave.

[Harry's Lad]

I ran my .22 Baraccudas through a chrono'. Are you saying that ChairGun outranks that method, Dave?
Just curious, really.

Of course not – the use of a chrono is essential for the intelligent use of ChairGun or any other ballistics software. ChairGun (or any other …) won’t give you any information that you couldn’t get ‘manually’. Personally, I've got better things to do. Accurate velocity estimation (at a couple of places in the trajectory) is essential. From the velocity (and a couple of other measurements) ChairGun will show you the shape of the trajectory, velocity & energy curves, etc. in graphical or tabular form.

ATB
Dave

[Zico]

Should be attending JG on Sunday....looking forward to giving it a go in the wee windless valley.

Anybody putting up £20 if it gets done there?

As far your challenge, 94 yards from sitted at the bench and my lucky bunny as support.....and no wind may take ya up on that

Had a wee blast again yesterday up at Kypeside, will let Zico post his thoughts on it.

http://pccures.pwp.blueyonder.co.uk/pics/windy.jpg

http://pccures.pwp.blueyonder.co.uk/pics/range1.jpg

http://pccures.pwp.blueyonder.co.uk/pics/range2.jpg

http://pccures.pwp.blueyonder.co.uk/pics/target.jpg

Yep, The breeze was non existant at home, phoned John suggesting it would be ideal conditions to give it a blast. I decided to try the vice with the Vermy clamped lightly on the front part of the trigger guard to allow for the light recoil but to ensure it muzzle flipped vertically only with the vice acting as a hinge.
My very 1st 3 shots were within aprox 1.2 inch (iirc John?) the breeze picked up a little.. I then got a few wind affected shots that took it out to about 4 iches The highlight of this 8 shot group was 3 shots through ONE ragged hole!
Great, we thought, looks promising!.. but it all went a bit pete tong from there as the breeze had really picked up and started doing all sorts of things.

JB started producing better groups in this unpredictable eddying breeze by trying to read the wind and aiming off... was getting better groups with his pro-sport than my (still clamped at this point) Vermy.. I unclamped it and copied his approach but the breeze became more blustery and my FPS had fallen enough to require a top-up.

I believe the ragged 3 shot single holer from my very 1st group of 8 hints at what could be possible if the conditions had allowed for it. Overall.. very encouraging!

[Harry's Lad]

The thing is, we don't know what conditions Harry was shooting under, apart from the 4,000ft elevation. Vaguely remembered from my flight training the density altitude ( which is what the pellet sees ) is derived from some other stuff like humidity and the pressure altitude ( rather than simply height above sea level )

Yes, of course. Altitude is used as a first-order estimate of pressure and hence density (which is what makes the difference to the drag/BC value). The temperature also plays a part but since we humans can only comfortably tolerate a narrow range of temperatures, I think we can safely ignore the temperature aspect of the density calculation in this particular argument. What say you?

I don't know how much difference this would make, but I personally would be inclined to trust TD's chrono, no offence Dave.

No offence taken but your last remark suggests that you misunderstand the current point (no offence ). A few pages back, bengarzy stated that he was inclined to disbelieve Harry’s claims because his (Ben’s) energy data was considerably different to Harry’s. Ben implicated Terry D in that message. Meanwhile, here in sunny Spain, my estimate of Harry’s ballistic data corresponded well with Harry’s estimate. Therefore (since the Laws-Of-Newtonian-Dynamics-As-We-Know-Them are the same as in Oz) it was clear that the pellet that Ben was writing about was not Harry’s JSB Exact. It turns out that Ben/Terry’s pellet was a H&N Barracuda Match – which has an inferior BC value and different dynamics/trajectory/energy retention to the JSB Exact under discussion. Post #184 explores the differences.

I think that it can be reasonably extrapolated that Ben’s original inclination to disbelieve Harry’s ballistics because they were not in his experience was, er, perhaps a little foolhardy. Maybe it's just me ...

Dave

[Sid]

No offence taken but your last remark suggests that you misunderstand the current point (no offence )

Dave

Well that's a definite possibility, I'm trying to pick out the ballistics stuff from among the personal stuff and it's slightly headache inducing
If it wasn't so interesting I would have given up by about page 4

[cpt-vera]

I ask this question regarding this Harry chap,
he was warned fair and square to comply to the rules we all have to, he didn't, and subsequently hes gone,

"who really gives a ?"

Barry

[Born Again]

That is; 50% difference in BC (when the BC is only 0.03) leads to huge differences in downrange velocity/energy/POI whereas a 50% difference when the BC value is 0.5 is barely noticeable.

Again – because of the difference in BC value – Harry’s JSB would be a lot less affected by crosswinds …

Who'd have thought it ?

[Harry's Lad]

Who'd have thought it ?

Que?

[Born Again]

Que?

Sorry, me being sarcastic. I was referring to some posts about Harry getting better BC because of altitude.

I understand that Harry tested the ballistic mathematics for Chairgun in association with the equations American author.

Ben, do your own figures allow for 4000ft altitude and the air temperature that Harry shoots at ?

Another point, does anyone have a formula to calculate how much wind effect on a pellet/bullet will be decreased at 4000ft ? It must have less effect, the air is much less dense.

I know it will have an effect, but the effect must be reduced. If we know by how much the effect is reduced we can apply a fudge factor to our group sizes to see if we can match Harrys.

The air density at 4000ft is 0.886 of that at sea level, humidity makes a difference too. I can't remember what Harrys BC was, I think he said 0.037..

0.032 (JSB Exact) / 0.037 (Harrys result) = 0.865

And while you're here, why bother with "flight time in a vacuum", if the pellet is at a constant velocity due to no wind resistance why not just incorporate muzzle velocity into the equation ? I think "flight time in a vacuum" is a red herring myself.

Steve,
(not argumentitive, just curious and enjoying hearing your expert opinions - not in a sarcastic way)