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Pellet Arc Help

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WCT_Editor

WCT_Editor

Member
Jul 10, 2015
116
23
Ohio
I need help figuring out the pellet arc with some pellets I'm collecting data for. The first problem I have is that I'm not sure I'm even asking the correct question so please bear with me if I screw this up. I'm using Chairgun Pro and taking the defaults for everything except muzzle velocity, zero range and end range. The data I'm using is for the .25 JSB Kings at 25.4 gr with a program BC of 0.0360, MV of 460 FPS, zero range of 30 yards (data set 1) and 50 yards (data set 2) and an end range of 50 yards for both data sets.

For data set 1 (30 yard zero), Chairgun shows that the pellet arc maxes out around 1.24" high at 20 yards with the zero at 30 yards and a drop of -8.67" at 50 yards.

For data set 2, (50 yard zero), Chairgun shows that the pellet arc maxes out around 5.20" high at 30 yards with the zero at 50 yards.

My question is what is the pellet arc high point and where is it located for data set 1 for a 50 yard shot?

Is there an option in Chairgun that I can choose to factor this or does it require one of the many math/physics wizards here to figure out? Am I overthinking this and it's a simple math problem as I can't see how the arc would only be 5.20" at 30 yards (like when zeroed for 50) when I have to compensate for an 8.67" drop when zeroed for 30 yards?

Before someone makes a comment about why so slow, the 460 FPS is with my S510 set on the lowest power possible which should generate around 9.79 FPE at 30 yards and 8.5 FPE at 50 yards. I feel this is a better setup for shooting house sparrows, starlings and pigeons inside a building than doing full power at 820 FPS and generating 30.92 FPE at 30 yards and 27.16 FPE at 50 yards and worrying about building damage and ricochets. On the downside, the 460 FPS is going to have a much greater arch than the 820 FPS which means shooting through openings may be more of a challenge so I'm trying to figure out in these scenarios if it is better to zero at the most common shot distance (i.e., 20 or 30 yards) and then hold over for the longer shots or zero for the longest shot and hold under for closer targets. I can see pros and cons with both options which is why I'm trying to figure out the arc height and distance so I can understand when to choose one over the other.
 
Chairgun has it correct. Sighted at 30 yd you need to holdover 8+inches for 50 yd. Sighted at 50 yd your trajectory apex/apogee will be 5+ inches above line of sight and that is the overhead clearance you need for the shot.
An interactive Demo is worth 10.000 words :) .
Open this Demo #6. http://www.arld1.com/trajectory.html
At the bottom you will see "CLICK HERE ..." to open in new window. So click that.
Now you have an interactive window. ... Edit : click the blue triangle "Next"
Above and below the rifle shown, you will see +ZR and -ZR for you to play with your Zero Range.
Firstly set the zero so that the trajectory coincides with the 30 yd and either measure the drop at 50 yd on the screen, or eyeball it with memory for apparent drop.
Now set the zero for 50 yd and then either measure the apogee/apex of the trajectory at its highest point above the line of sight (at about 32 yd); or remember the previous 50 yd drop (at 50 yd) for a comparison. You will find the comparison to be in the order of 5:8.

Now for the important part you left out of your actual "shooting in the barn" equation: When shooting at high targets or at low targets you will impact higher (above) the point of aim than you would for a target on the level with the rifle. The higher, or lower, the target is the more you will have to aim low in order to connect.
That is another thing you must consider.:

Demo # 21 http://www.arld1.com/targetplottrajectory3.html
 Demo # 18 http://www.arld1.com/stevescompensatingsight.html  This was a special compensating sight/base that I tested for Steve Woodward years ago. It worked satisfactorily but was rather delicate at the time and he did not proceed to market it.

If you wish to acknowledge the author/s then Steve Woodward (Steve_ in_NC here in this Forum) is the maths brains behind all the Demos. Perry Babin transposed them to interactive Demos about 10 maybe12 years ago. The whole suite can be found in the dropdown of the "Forum Rules" on the Yellow Forum, as "Airgun Demos".
http://www.arld1.com/

I hope this helps. Best regards, "Yrrah" (Harry).






 
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In my response above I have added Demo # 21 to show how shooting up into trees etc or downhill causes high shots; and the effects of cant are also incorporated.
Please let me know your reactions to these excellent graphics and whether they were useful in answering your original question Demo #6; and the extended question relating to inclined shooting. .................. Regards, Harry.
 
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Thanks Yarah,

If I'm understanding this correctly, when sighted in for 30 yards and you take a 50 yard shot, the trajectory apex/apogee will be the same as if you were sighted in for 50 yards. If this isn't correct, is there a formula I can use to calculate it?

As for the demos,the really didn't show me anything I wasn't already aware of, but were pretty cool anyway and I'd think very useful especially with new shooters. Demo 6 is very easy to understand, but I can't enlarge it take measurements like you recommended.So while it shows how trajectory changes based on distance, I couldn't do more than make the trajectory move up and down. Demo 18 took a bit to understand with the red and green lasers intersecting the trajectory with Demo 21 being the most difficult as the cant shows up very easy, but the angle doesn't become noticeable until you get around 20+ degrees.
 
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When you think about it, the pellet has to take the same trajectory from the muzzle to the target if you want to hit same, regardless of whether the rifle is sighted for that range; or you have it zeroed anywhere else and hold over, or use mildots or hash marks or other. If the pellet did not take the same path it would not hit your target. So the trajectory is the same , the barrel must point the same, and from any practical viewpoint, the light from the target has to come through your scope with a similar relationship to the pellet's trajectory.
As your rifle is at present, velocity and pellet, and sight height above bore 1.80", if you sight in at 50 yards the apex of trajectory will be roughly at 27/28 yards. Scope height above bore line makes a little difference as does pellet velocity .. If you sight in at 30 yards and hold over to bring the trajectory to intersect the 50 yd target, the apex will still be roughly at 27/28 yards and about 5+ inches high of the sight line. So you will need say 6 inches clearance under a beam at 28 yards to be safe.
Other readers with other rifles shooting at other velocities will have different parameters.

Edit: Ref shooting at elevated targets ( or downhill ) up to about 20 degrees you really don't have to worry much about hitting too high. The nearer you get to vertical the more it matters. If you didn't make any allowance, at 90 degrees the pellet would land behind you when it came down as it would have an inverted trajectory. ........... Kind regards, Harry.
 
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Yes, I slipped that in as I was unsure of what his scope height is (and for others) ... " ... Scope height above bore line makes a little difference as does pellet velocity" ..
Perhaps I should have emphasized it more. Silhouette shooters here often have very high scope mounting to make use of the further-out single point zero in enables.
Your field target shooters may or may not do that also. I can see an argument for both higher and lower mounts for them. ... Regards, Harry.
 
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