Real world trajectory data

I found this out months ago. I have noticed my POA and POI were different then what Strelok said from my zero (50 yards) and under but after my zero, Strelok was spot on. I made a video on this subject. Its very tedious to go about figuring out your pellet drop but this will give you trigger time and a guarantee way to know your gun's pellet drop. I normally do this whenever I change anything on my gun (pellets, scope, and/or tune)

I did a little bit of testing today with my matador. The winds were averaging 15 mph and gusting to 26 mph and almost full value. According to Strelok, I'm suppose to hold four mils in a 15 mph wind but I was actually holding 2.5 mils at a 70 yard target.

Hi all

I make up a Dope Card , then laminate so weatherproof. One side is at 10 x t'other 20x . Do it once do it right. 

Safe shooting

I never found that Chair Gun gave a "perfect" trajectory plot with my recoiling springers. I suppose the reason is that the recoiling springer "flips" the pellet exiting the muzzle in ways that can't be calculated so I made up a simple target to check the trajectory "real world"........

LOL....this is how I know the Chairgun output wasn't a good match (or perhaps the shooter input). Still, if I need to actually shoot to verify the 'puter output, then what's the point of usin' Chairgun in the first place except for getting a "general idea" for a specific tune.

I do use my ProChrono frequently to gage the "health" of my springers by the consistency of the velocity from shot to shot and I really don't care if the actual velocity is off a couple fps one way or the other. With my shooting skill from "bucket and sticks" I found that as long as the velocity is consistent within 10fps my accuracy isn't affected. Here is a pic of a shot checking out my HW95......yep, velocity is right where it's supposed to be after a couple weeks since the last check.............

I use strelok Pro for my centerfire rifles and my airguns. I was checking my Wolverine for zero and accuracy out to 80 yds the other day and confirmed Strelok Pro is dead on with my real world hold over. My Wolverine was zeroed at 42 yds and according to Strelok Pro the pellet would have 9.3 MOA drop at 80 yds. I got set up 80 yds from the target and used the 9 MOA hold over point in my scope and hit right where it should for 80 yds. Then I tested it by adjusting the turret 9 MOA instead of holding over and again it was right on. I did that for several groups and they were right on to the drop calculated by Strelok Pro. You have to have everything correct in the data to get usable data in the field.

I didnt see it in chairgun but Strelok Pro has options for when zeroing your scope that includes what the temp, humidity and pressure is when you sight in the scope. I always include that info during my zero session and I also make sure I have those parameters set correctly for when I shot over the chrono for my velocities. Strelok Pro makes adjustments to the hold over based on those input numbers and Streloc Pro even adjust drop according to spin drift and other factors that become a problem in really long range shooting for centerfire rifles. So you have to get all that data in there correctly to get correct hold over info. Streloc Pro is a very in depth drop calculator that needs all the info to give you the correct drop. 

I shot my 34 in .177 last week from 10 to 50 yards to get my hold overs. After I finished I opened Chair gun and checked my results, 10 to 45 yards were almost spot on and 50 yards was less than 1/2 mil off. 
I'll check the 48 when I get a chance.

"fishinwrench"After a lengthy chronograph session, or more like 5 of them, the trajectory data on chairgun and strelock wasn't accurate, so here's what I did...... 
I carefully shot a 5 shot group at 30yds and another at 40yds, then accurately measured the drop. I then pulled up Chairgun, entered my projectile and scope height data and then altered the FPS until the drop between 30 and 40 yds. matched the ACTUAL drop measurement.
Ureaka! My trajectory chart is now spot on at all ranges, and I mean DEAD ON from 15 to 75 yards (and probably beyond, but 75 is as far as I will ever shoot).
Now, whether chronographs (even the very good ones) are bullpoop, or the B.C. is the reason......it doesn't matter. Who needs a damn chronograph if the numbers are unreliable ? The real world FPS of my set-up is 86 FPS different than what the best chronograph on the market says it is.

Click to expand...

I hate to tell you, but from my understanding one is supposed to "calibrate" the app to the "real world" anyway. At least that is the case in Strelok. When you look in the settings somewhere (I do not have the app in front of me), there is a section where you can correct either the FPS or the BC. For that exact reason you have pointed out. App and real world results may differ.

Kmd

fishenwrench -- I share your frustration when things don't seem to work as expected, especially when it comes to software. That said, I've often found the old adage of "garbage in, garbage out" (GIGO) is the problem.

I am a big fan of ChairgunPro and have been for many years. I don't shoot benchrest, field target, and don't often shoot off a bench for long range groupings but the data ChairgunPro provides lets me know what to expect in the field and has proven to be quite valuable to me. It may not be 'spot on' but is extremely close and I feel I need to know what to expect when in the field. I try to input the most accurate data I can and one of your comments was regarding chronograph variance made me think of things I've noted in the past.

My first chronograph was a Chrony brand when if first came out way before I got into airguns. At that time I was only shooting powder so the Chrony was roughly 7-10 feet past the muzzle It didn't have the skyscreens you see today but what it did have was two aiming guides made from some sort of paper product that had an oval cutout in the center with markings on the face to indicate where the scope and barrel should center. It also had a plastic skyscreen that fit on both the front and rear of the guides. I had to line up the oval holes in both guides which placed the projectile about the same height over each sensor (sweet spot). Given the distance away from the bench this was not so easy. The design of these short chronographs requires the projectile to be as close to equal height and center as possible or else the fps reading will be off. I think this 'might' be why you see variance in speed. A tilted sensor can also cause a variance and I know this from experience on my last Crony brand chronograph that had a loose rear sensor. The following link shows an example of what can happen.
Chronograph Accuracy Tips – 15 Practical Tips to Increase Accuracy & Reliability[/QUOTE]http://precisionrifleblog.com/2012/...ccuracy-reliability/embed/#?secret=5kNQSCYa5Q

Another measurement that can affect trajectory alot is the sight height. On a springer where the compression tube is separate from the barrel, the height of the scope above the tube is often different from the height above the bore at the muzzle. I've found the 'tin-foil' method to be the best way to get this measurement. A quick search can provide you with how that is done assuming you don't already use it.

Of coarse the BC is also important but not as critical as getting the velocity and scope height correct. I can say that it's very gratifying to see real world data correlate to ChairgunPro's output.

I believe we all try out best to input the correct data and I didn't mean to imply you don't. I'm working with what I see in this post and replied with the intent of helping. Looking at the variance in your chronograph speed to the the speed input to Chairgun to match your real world data seemed far enough out to question the methods used.

As a side note on getting chronograph data, another point worth mentioning is the light source used needs to be fairly equal on both sensors. If indoors and using one light source in the middle of the sensors can cause false data output as well. Again, you probably already know this but I mention it for anyone reading this down the road.

I have a doc appt in 25 minutes so got to run...

fishinwrench: After I got back from the doc appt and some shopping, I played with settings in ChairgunPro on several of my break-barrel springers (R9 in 177 and 22, and R1 in 22). I altered the scope height from 1.0 to 2.75 then tried all the BC profiles using the Crosman HP often found locally on each gun looking at height variance at 55 yards. Aside from two profiles (round ball and plain cylinder) about the greatest variance at 55 yards was one inch which isn't the 2" drop you see.

At the first of this string of posts, you mentioned you used three different guns and four different pellets but all showed the same result. Later you mentioned you put a new seal in a Benjamin Prowler which is the one you altered the velocity in ChairgunPro to match your real world testing. The implication is that all these guns have something in common that is affecting the variance in the ChairgunPro trajectories. If it was only one gun - one might consider how tight a seal fits the tube, a weak alive jam, bad breech seal, bad scope, loose screws, what they are resting on when shot, pellet size, and of course chronograph readings. But it's not just one gun -- all are affected so the velocity readings seem to be the most logical suspect. I don't know what chronograph model you have but you did mention it was pricey. I guess one other possibility to consider is how the gun is held but I will assume you got that covered.

You also mentioned a variance of 0.3" at 55 is acceptable but 2.0" is not. I've only shot a few long range groups at 50yards on the BLM (80 mile round trip) with both springers and PCP and the best I've ever gotten is close to .75". I would be tickled pink if I could hold it to .5" on a day with no wind. On a typical day on the BLM with light winds at 50 yards -- groups are more like 1.5-1.75" with flyers often pushing sizes to bigger groups. How the wind affects these light weight projectiles is a real eye opener.

I'm in Idaho and I wish you were closer so we could spend a day troubleshooting this but maybe you know another airgunner close by that could help. A fresh set of eyes on a problem may reveal something missed.

Good luck....

It helps a great deal also to make sure your scope’s magnification (if using SFP scope) is calibrated to reflect true mildot spacing in relation to the target. Note: Many scopes, even high-end ones, don’t have true mildot spacing at the mag level they claim.

Here’s a link that takes you to downloadable calibration sheets to use at different ranges:

http://www.anstonftc.co.uk/targets/

And here’s an excellent way to measure scope height for Chairgun:

https://airgunaccuracy.wordpress.com/chairgun-and-scope-height/

Fishinwrench, I gave a lot of thought to this reply before deciding to send it. It is long in order to give a well considered response.
I hope it is received in the spirit with which it is sent.
It may serve to give a little more credence to the use of trajectory prediction programmes, of which Chairgun is an excellent example in the airgun world, and to build a little more confidence in the use of such ballistic programmes for those who might want to try them.

Back in 2004 when this popular subject was doing the rounds I carried out the following study:
November 2004 after doing all the necessary homework and data collection I applied it to a programme that Steve Woodward had designed* and Perry Babbin had resolved into his excellent graphics models.
Dave Eades' Chairgun programme is a further development to that model and uses the GA standard rather than the G1. I had a little to do with supplying Dave Eades ( Harry's Lad) with velocity and bc data I collected from shots over a chronograph from 50 out to 200 yards to determine the progessive changes in bc with range and velocity.

November 2004: After establishing all the necessary data that of course included average mv, scope axis height at the muzzle, actual scope click value and zeroing at 50 yards under the prevailing ambient pressure, altitude, temperature and humidity, the following protocol was followed:
With my target taped to a box it was first set at 100 yards ( all yardage was laser measured ). I had been doing virtually all my shooting at 100 yards or 71 yards to that point in time.
OK one shot was fired at 100 yards; walk down move the box back to 90 yards, check the range back to the 100 and then to the chair in the shed, walk back to the chair and re-check to the box ; re-set the sight clicks for 90 yds according to the table made from the ballistic program * and double side taped along the top of the scope. Shoot one shot at 90 yrds. Walk down and reset the box to 80 yrds etc etc to 70, 60 50, 40, and 30 yards.
Shooting was done with two classical leather sand filled benchrest bags and my interpretation of benchrest technique. Before triggering each shot the rifle was set to centre the cross hairs in the middle of the 1 inch square on 16 x power. The rifle was then gently "bumped" in two or three places. If the sight moved to settle more than approximately say an eigth of an inch at the target plane it was re-adjusted and tested again until satisfactory. It was then gently cradled and the shot fired.

The target bellow shows the eight shots all impacted in the one inch x one inch square that was the criterion aiming mark.
I think that is a pretty fair indication of the potential fiield use of a ballistic programme. No shot has impacted further than approx half an inch from the POA at the middle of the 1 inch square.
Chairgun is sophisticated and developed to allow ambient data inputs enabling previously necessary real time on-the-spot preliminary testing, such as you are using, to be pretty much abandoned.

The caveat is that the full set of data input is necessary to allow it to show its best. Armed with a small weather station to give me ambient conditions of temperature, pressure and humidity (in order of importance) , my own pellet to range /ballistic pellet coefficients for my rifles and the other data indicated above, and rangefinder, I can go to any location and be confident of the results out to extreme ranges. Providing wind reading skills or lack thereof don't let the side down.

The rifle used was an FX Excalibre/FX 2000/Tarantula, which has shot over 70 sub inch 100 yd groups before and after this study; and literally hundreds of rabbits to 150+ yards . Pellets were 15.9 gr JSB Exacts shot at 900 fps average. The rifle has no regulator and so has a very tight velocity consistency in its plateaued range, 170 to 150 bar.
Please expand the target for better view. ........... Kind regards, Harry.

Nice Harry. Thanks for all the work you do with real world ballistics.

That is thw best way to verify ballistics. Plus it is useful to determine velocities if you don't have a chronograph. Just my opinion.