Advanced Marksmanship Need some help with my dope.

[Mr Smith]

Hello and thank you for any help you can give.

Nothing had changed with my gear since the last time shooting where all of my dope was spot on for the TVP intimidator match a few weeks ago, yardages were anything between 275 yds. and 1165 yds. I actually connected with the 1165 on a second round hit after adjusting for wind. The temperature was cool 50's and cloudy that day.

I shot two different long range competitions this weekend, Rayner's long range match and the TVP Headhunter match. At both matches I used a Kestrel 4000 and the shooter app on my Ipad. I checked pressure, humidity and temperature at each stage throughout the day and edited the shooter program to reflect the changes. The pressure pretty much stayed the same all day, the temperature and humidity changed a bit.

Here is an example of the difference in my dope from actual on the fourth stage of the headhunter course.(6"w 9"h target) Most shots were around .4 to .5 mils high both days at these ranges.

dope actual
423 yards 2.6 mils 2.1 mils
514 yards 3.6 mils 3.2 mils
557 yards 4.1 mils 3.7 mils
600 yards 4.7 mils 4.3 mils
560 yards 4.2 mils 3.8 mils

Conditions at this stage: Pressure 29.13, temp. 70f, humidity 21.4, very little mirage.

Now it was not just me that was having this sort of problem, almost all of the competitors were shooting high at both ranges both days and these were no spring chickens when it comes to shooting.

I was asking some of the regulars about this and there was speculation that since it was a crystal clear day and the sun was beating down on the valleys below there might be some thermals boiling up out of the valleys we were shooting over.

My question is: would thermal convection coming off of a large valley that we were shooting over cause the air in that area to be warm and thin enough to make a .4 to .5 mil difference in my dope at 400 to 600 yards?

John.

 

[Advokaten]

IF it had been just you, it would have been likely to be rifle/shooter related, ie perhaps a poorly tracking scope, fudged zero or perhaps a copper build up in the barrel, sending your pressure way high and the bullets to.

Being that you say it was a all round problem, I would suggest that DFOOSKING is right, the sun/temp created a thermal distortion/refraction of the targets. /CHris

 

[Lukas Koukal]

The mirage could play havoc with targets for one thing, for another - are you sure about your MV? The hot day could influence your powder burn rate in the first place, sending those pills over the distance faster.

You´re using the Shooter app; go to table/graph showing you the dope, hit tools and select the muzzle velocity tool. Adjust up until the dope for the longest distance shot matches the actual data as gathered. Now check the shorter ranges - do they match, too? If it is so, the ballistic curve is correct and verfied over the distance, only for a different MV than you´ve thought.

 

[Sterling Shooter]

Did you account for slope?

 

[proneshooter]

The HH stage 4 600 yd shot is almost dead level from firing point to target.

 

[Mr Smith]

I did some playing around with the muzzle velocity in the shooter program and had to go from 2600 fps to 2714 in order to match up within a tenth of a mill to my actuals. My actuals could easily be off a tenth and still hit those sized targets. I'm shooting a 20" 308 with 44 grains of Varget under a 175 Matchking.

I did open a new 8 lb. jug of Varget recently but that should not account for that much velocity increase.

I also started using the sunshade on my scope (NF-F1) but I can't imagine that being the problem.

It has been awhile since the guns got a good bore scrubbing.

I guess the fact that almost everyone at the range was adjusting their elevations down a considerable amount with no difference in atmosphere is what confuses me.

I will have to run it over the chronograph and see if there is an increase in velocity.

Thanks for your help and any insight. John.

 

[Mr Smith]

The HH stage 4 600 yd shot is almost dead level from firing point to target.

Hey, you were there Sunday! Did you have any troubles with your elevations matching up with your dope?

 

[Changed]

I recently experienced something very similar. I had data on a 500 yard target of 3.7, which was recorded in January. In April I engaged the same target, and had to adjust to 3.2. So I calculated the deltas to be 45º temp, 30% Humidity, and ~.98 pressure. At the time I had 290 rounds since last cleaning. The only thing I can think of, aside from the atmos deltas is the fact that I had the rounds lying in direct sunlight. In fact my magazines were hot to the touch.

 

[proneshooter]

Hey, you were there Sunday! Did you have any troubles with your elevations matching up with your dope?

Yes, but nowhere as much as you. I was off by .1 ~ .2 mils.

I left halfway through but when I smacked target 5 on stage 2 (521 yds) my dope was right on what JBM said it should be.

I'd chrono your new lot of Varget and see what you get.

 

[Mr Smith]

Yea, I'm gonna run this new lot across the chrono and see what I'm working with. It seems like a lot of speed for just lot to lot variation. Who knows could be all that it is.

Thanks, John.

 

[psmith]

To see what atmos conditions have to do with things start using just one number--DA(density altitude). This will help get a measure of what the air is like relative to standard conditions. I'm not sure shooter can use this but if it can it will save some work of entering in all the variables. I've spent a ton of time going by only ballistics programs for dope since I can't shoot out to all the distances as often as I like. To get a .4 mil change at 600 yds the da would probably have to increase to about 7000-8000 so thats probably not it. It would probably account for a tenth. Also you need to make sure your zero is rock solid for the programs to work, it shouldn't be a tenth or two off. You can chrono the new lot but just use the velocity as relative to your old lot, not an absolute #. Go to the range, confirm scope tracking, get zero, then shoot to about 80% of the cartridge's sonic range ~800 yds for 308. Record the conditions and dope. Stiff crosswinds will affect the elevation slightly so try to account for that. Have the program compute a velocity given the dope at range. Confirm at 600 and 1k and you should be gtg.

 

[Mr Smith]

Update.

I ran it across the chrono and it came out to be an average of 2575 FPS. This is what I had been using for dope the last two years. I reset my dope to 2600 that day after the first stage because of everything going high, obviously it was not enough because the results told me I needed 2714 to match up. Shoot, thats a 139 fps difference!

I shot the TVP sniper match lasts weekend and my dope was spot on using the same program and 2575 fps, Same place, some of the same targets!

I am able to use DA on the shooter program and I have a Kestrel that does DA so from here on out I'm going to use DA. It's quite possible that I made an error that day but that is a mighty big error.

Both me and my partner use the same setup and our scopes are NF F1's that have never let us down yet, and tracked perfectly last weekend so I don't think thats the problem.

I was just scratching my head that day, I know to believe the bullet but .5 at 600 is a lot to believe. Have any of you had a day where you just could not get your dope to match up like I had that day?

 

[proneshooter]

I really don't think density altitude had much to do with your error that Sunday. It would have to have been ungodly hot that day for incorrect DA to be the culprit.

And it wasn't.

 

[turbo54]

I'm sure your NF F1s are fine.

It's TOUGH to sell me on thermals or DA shifting required dope .5mrad @ 600 yards. That's huge.

Personally, I've witnessed (and owned) a rifle exhibit a .5mrad zero shift from one day to the next. Shoots little groups where you're aiming today, and tomorrow it'll shoot little groups .4mrad higher than your aiming. You reset the zero on the turret, and the next day you're shooting little groups .4mrad lower than you're aiming. Nothing is loose, it just shifts. Bedding/ action-to-stock relationship? (I know you've got AICS) Maybe.

If I were you, I'd make a point to affirm zero each time you take the rifles out and see if its moving on you.

Most importantly, check zero on a day when your dope seems off.

 

[Mr Smith]

Yea I was worried about the zero myself but my wife's gun which is a carbon copy of mine was doing the exact same thing! Although she was watching how high mine were going and making the adjustments and making the hits. Hence her score of twelve and mine of six! lol.

And the entire group we were shooting with that day were shooting high. No they may not have been off a whole .5 mill at 600 yards but watching through the spotter I was seeing an awful lot of shots going over the top of targets and a lot of confused looks coming from shooters.

I agree that thermals coming off of the valleys could not "lift" a bullet that much if anything at all.

I'm going to watch out for this in the future and make sure I log every variable I can find and see if I can put this problem together. I'm also going to ask Tom Sarver if he has seen this happen at his range and if he knows what might have been happening that day.

Thanks for your input.

 

[turbo54]

Did you range them yourself or were the ranges provided?

They're well established, known distance targets.

They're all within 1-2° of horizontal, also.

 

[proneshooter]

Use grow lights


Sent from my iPhone

Jt

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