How close is your trajectory profile?

To be honest I've never been a good enough shot to really know, but of late I've had access to a farm to do a bit of trial and error testing.

Up until now I've mainly used a 7stw for long range and it just did what it was told! I must have got lucky as I never had any issues all the way out to 1100. But that's been sold, so I'm using a 7mmwsm, which was fine out to 600, but I knew my velocity values were a bit wrong so error started to show in my predictions (groups were always good but somewhat pointless if not on target), so I put some time aside to fix this.

Using a G7, and after lots of fiddling in the ballistics program I'm getting about 0.25moa error at 400, bang on at 500, and bang on at 800. This is the best I can get it. I can't stretch it any further safely on this property so beyond 800 is an unknown. Absolutely stoked with my groups, all <0.5moa at all those ranges.

The weird thing is that the Litz programme recommended using 2940 as my velocity, but that would have had me up to 0.5moa up/down of centre. So I played around and if I use 2970 it gets me within 0.25moa.

Anyway, how's everyone else finding their predictions, are they one the money...our do you to find a bit of fiddling around is required?

Kj

Sorry, cant help. i had Norm at NZ Hunters team do my head scratching ( yes it cost ) but my come ups are on the money.
Pity it dosnt always equal results !
Im not ready to do a writeup of my long weekend Jap hunt yet (still sulking ) but after shooting a small 8pta at 520yds on sat i thought i was the man and then nek minit i videoed myself miss a ripper wall hanger.
cry,cry,cry,cry,cry,cry,cry,cry,cry,cry,cry

Yup, shootings a confidence game if ever there was one. Some days you're on fire...others you wish you'd just slept in:)

have a go using pointblank on www.huntingnut and see how it compares...I just use the online version but haven't heard any negatives from system at all.

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Originally Posted by Micky Duck

have a go using pointblank on www.huntingnut and see how it compares...I just use the online version but haven't heard any negatives from system at all.

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Cool, thanks for that. I was using shooter and after a bit of playing around I'm getting what I want/need. It's just that for this load its not been as straight forward as it usually is.

Well try that program and see how it goes. But well continue to use shooter app on my phone now it's pretty much sorted.

I think two main issues are likely to be my chrony and possibly my range finder. But it doesn't matter now as ling as I only use that range finder, as the load and everything else is all dialed in tune with each other.

Cheers for letting me know about other app though.

Kj

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Originally Posted by Micky Duck

have a go using pointblank on www.huntingnut and see how it compares...I just use the online version but haven't heard any negatives from system at all.

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Cool, thanks for that. I was using shooter and after a bit of playing around I'm getting what I want/need. It's just that for this load its not been as straight forward as it usually is.

Well try that program and see how it goes. But well continue to use shooter app on my phone now it's pretty much sorted.

I think two main issues are likely to be my chrony and possibly my range finder. But it doesn't matter now as ling as I only use that range finder, as the load and everything else is all dialed in tune with each other.

Cheers for letting me know about other app though.

Kj

Just finished watching the applied ballistics dvd, disc three covers exactly this topic. It was awesome, clarified my issues and I'm now very happy with what I did to fiddle my trajectory curve.

Wish I had watched it a week ago!

Kj

Out of curiosity, did you have to fiddle with the BC to get it to fit?

To me that would seem the only solution if it's bang on at a couple of ranges but out at others.

There is a truing function in the app that i've used, but it didn't quite fix a couple of issues I had. Still need to play with it more if I ever get a chance at long range on a nice still day.

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Originally Posted by MattyP

Out of curiosity, did you have to fiddle with the BC to get it to fit?

To me that would seem the only solution if it's bang on at a couple of ranges but out at others.

There is a truing function in the app that i've used, but it didn't quite fix a couple of issues I had. Still need to play with it more if I ever get a chance at long range on a nice still day.

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Yeah Ive used that mv calculation tool previously and it worked magic straight away, but on this load it was both high and low which had me buggered.

So I doubled checked the scope movements, which were verified as a true 1.0moa, so that ruled out the scope.

The bc was a Litz bc value, so I simply accepted this as true.

The range...well who knows, but in previous tests my rangefinder is always within a metre or so of everyone elses, so I pretty much acept that as true enough

The kestrel gives me good atmospheric data, so I accept that.

That pretty much left mv. The Litz tool helped but I had already stumbled upon a possible solution that gave better results for this range of results (real life test data). Litz mv tool suggested 2940fps, but by upping that to 2970fps which gave me zero error at my longest range, everything else at closer ranges basically fell into line.

Not sure about longer ranges like 1000y plus, at this stage, will have to verify this later

Kj

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Originally Posted by kimjon

Using a G7, and after lots of fiddling in the ballistics program I'm getting about 0.25moa error at 400, bang on at 500, and bang on at 800. This is the best I can get it. I can't stretch it any further safely on this property so beyond 800 is an unknown. Absolutely stoked with my groups, all <0.5moa at all those ranges.

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If you are shooting smaller than 1/2 MOA groups at 400, 500 & 800 you need to come show the guys in the NZ team a couple of tricks...

Care to post some proof ? It's real easy, take an A3 page. Put 5 dots on it. Shoot 5 shots at each dot. Take a photo and post it...

Why 5 shots? why not 3 or 30?

OK VC, you can do 30, the rest of us will go for 5 :D

You know why ... 3-shot group is one thing. Consistently shooting 5-shot groups is exponentially harder. If you really want to see what you can do, shoot 10-shot groups - that seems to be the norm for most recognized forms of "accuracy" competitions - smallbore, NRA fullbore, olympic ISSF etc.

So if ten shot groups is "most recognized" as a test of accuraccy why only shoot 5?

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Originally Posted by ebf

If you are shooting smaller than 1/2 MOA groups at 400, 500 & 800 you need to come show the guys in the NZ team a couple of tricks...

Care to post some proof ? It's real easy, take an A3 page. Put 5 dots on it. Shoot 5 shots at each dot. Take a photo and post it...

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Im no where near NZ team standard, but I had an exceptional day with zero wind and probably a bit of luck too. I was only doing three shot groups to validate my trajectory, not trying to compete at the Olympics:) ... but I can hand on heart say my groups were all less that 0.5moa. But I get your point, these would open up the more shots fired for sure.

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Originally Posted by kimjon

But I get your point, these would open up the more shots fired for sure.

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Would probably change your observed mean point of impact a bit too

Hmmm another little trick you can use is increasing the zero range...

Think about it this way...

If you had a "100 yard zero" and I asked you how much you would hold over to shoot a target at 140-150 yards? You would say none because it's a a pretty flat shooting caliber.

However punch this into the calc and it will change things considerably.

It is also better than fiddling with the BC and MV as it shifts the predicted trajectory rather than changing its curve.

:)

We had trouble with a long range rigs impact when getting out past 400 yards. We looked at all possible explanations as to what may be causing the inconsistency between the ballistic readings and the actual impact point.
We then changed to a different crony and discovered 170 fps difference in the velocity readings which made a huge difference to the dialling and subsequent impact point.
Also wonder what distance is the optimal distance from the muzzle as the bullet will take a bit to reach max speed. Chronograph instructions seem to be quite flexible in directions about the distance from the muzzle.
Another interesting observation when firing factory ammo through 2 different 300wm's was the large variation in velocity between the barrel lengths. One rifle with a 24 inch barrel was achieving velocity of 3225 fps with 150 grain projectiles and the other with a 27.5 inch barrel was getting up to 3400 fps.

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Originally Posted by yogi

We had trouble with a long range rigs impact when getting out past 400 yards. We looked at all possible explanations as to what may be causing the inconsistency between the ballistic readings and the actual impact point.
We then changed to a different crony and discovered 170 fps difference in the velocity readings which made a huge difference to the dialling and subsequent impact point.
Also wonder what distance is the optimal distance from the muzzle as the bullet will take a bit to reach max speed. Chronograph instructions seem to be quite flexible in directions about the distance from the muzzle.
Another interesting observation when firing factory ammo through 2 different 300wm's was the large variation in velocity between the barrel lengths. One rifle with a 24 inch barrel was achieving velocity of 3225 fps with 150 grain projectiles and the other with a 27.5 inch barrel was getting up to 3400 fps.

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3400 fps ? What factory ammo was it!!?

I emailed the Crony people a couple of years ago about the distance from the muzzle
they told me 15 feet

Hornady American whitetail. On the box it said 3250 fps. Out of my Tikka it was doing 3225 and up to 3400 fps from my mates rifle.
Seemed mighty fast but then velocity from my rifle was fairly close to what was suggested on the box.
It shot very well consistently hitting a 12 inch steel plate at 600 yards.

Hi Kimjon,
It will be interesting to see if anyone posts their actual trajectory and also ideas for getting it right.

I've used the Shooter app and a program on CD which came with Litz book Applied Balliastics 2nd Ed. These give the same results. I think Shooter uses Litz method but now that Litz has his own app maybe they will diverge.

In simulation terminology, you "train" your model with a preliminary set of data (Data on previous engagement). In the case of ballistic models, this training is adjustment to the BC & MV till you've got a good fit with your own personal dope. Then you try it out it with new "test data" to see how good the predictive value is. Then you can go out and apply the model and shoot deer with it. Sounds a bit mathematical but its common sense really.

I only ever used a chrony result as a starting point for velocity and adjusted inputs manually till a number of 2820 (860m/s) matched the trajectory I'd observed.
I've estimated the G7 BC of my 140 gr BT bullet from Litz published figures for Nosler BT in 120 and 150 gr. As suggested above a different BC might bend the trajectory differently further out and fit third points better. But, I decided that for a start, trying to adjust two input parameters at once would just be a way to getting lost. I'll try out a few scenarios later but don't have time tonight.

Here are my principles for collecting dope:

• Check each distance with a rangefinder and write it down.
• Get the tightest group you can. You might not want to ever shoot 1 MOA targets but if you can tune your trajectory better than that its very helpful. A 10" group at 500 yd i great for hitting gongs or deer but not much help for predicting trajectory at 800 yards.
• It goes without saying you need to use the same shooting technique especially rests, bipods and positions at all ranges.
• Always establish a very exact 100m zero before you start a session. This needs to be with 5 shots at least. Small errors like 2-3 cm here will leverage out to significant uncertainties about velocity and BC at longer ranges. Preferably finish with another 100m group to verify there has been no zero change during the session. Again, 2-3 cm might not seem much but when did it move - was it before or after the 500m group ? This is also where it becomes difficult if you have progressive barrel heating or fouling issues. Shooting a 5 shot group is one thing but establishing dope is another level of challenge.
• You require absolute control of your sights. They must dial the point of impact up and down just what you expect. It doesn't have to be exact 1/4 moa or IPHY but you need to have verified and proved it for yourself with the whole system, shots on paper.
• Use one load and stick with it. Load developments and trajectory doping are incompatible.
• Record key ballistic variables at each session, specially temperature and altitude. I once did some testing at 400 and 600m ranges at 1100m ASL and later when adjusting my nominal MV put those figures back into shooter to see which value gave the observed trajectory at altitude. If at all possible, shoot 100m and two longer ranges at the same session, on the same day.
• Use paper. Gongs and even electronic targets are too temporary. You need to take the paper home and apply rulers to it a few days later when you are calm again. The results always look better and more comprehensible after a good night's sleep.

Here are pics of a recent check at "short range", before the Ruahine Biathlon.
First target is re zeroing at Taupo NZDA range on the way down. Altitude 400m 15 C and sunny. Virtually no wind, from 6 oclock. I couldn't resist spending a couple of leisurely hours there. A calm good shooting day in the hand is worth two in the bush.
http://i812.photobucket.com/albums/z...20Bnchrest.jpg
The bottom group of 5 is the last. Then I packed up all my gear and was off to the Taihape branch range. I didn't want to muck to muck around on the 100m range, just set up and shoot once. The land owner kindly showed me to the "400" target frame and back to the giants' bench. It was now 7 degrees C and raining lightly. Altitude was 750m.
For 356 m I dialled up just past my 350m value glued to the rifle butt, using 1.9 mRad. It was too cold and wet to get out the phone for the app.
http://i812.photobucket.com/albums/z...20Bnchrest.jpg
Wind about 2-3 m/s apparently from 11 o'clock so I had made no allowance, but after seeing the paper perhaps it was corkscrewing around ...
I also wonder now whether there could have been some lift from the wind as the firing point is at the top of a slope (a bit like some places at Hangawera) and the first 100m could have been subject to perhaps a quarter value wind updraft.

Seeing this result and having had some higher than expected groups in the past, I decided to allow about 0.1 less than my chart, which served me well the next day when I hit 9/10 gongs at 290m (skite I know but it feels so good to hear that thwak ! that I just have to tell you about it). I wasn't the top score but equal to Phillipo, who only beat me by running faster.

So, my trajectory was good enough out to 350m anyway.

Mate, what an awesome reply. I really appreciate the effort you've gone too.

Kim