Sorry I just realized you are using a 200 yard zero. Still your real world data is more consistent with a 100 yard zero. As mentioned above it could be a stability issue and your zero is off as well as your velocity???
Real world drops and Shooter app vastly different. 6.5 Saum, 156 EOL Bergers, RL26
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7mmTikkaShooter
Well-Known Member
There are two basic ways to true a ballistic calculator; first you can just adjust the velocity so it matches up, or you can adjust the bullet b.c. in the calculation. I actually prefer the latter because with a chronograph you can actually gather data to input and it's impossible to know how much the b.c. is effected after the bullet gets slightly deformed after being pushed through the rifling. That deformation is slightly different with every barrel and immeasurable outside of measuring the difference in drop. In your case however, I've run your load through my Applied Ballistics app and can't make any adjustments that can make sense out of your results. Either your velocities are off by several hundred FPS or the b.c. is off by....a lot. My only conclusion, assuming that you've turned over every stone like it sounds you have, is that there's something happening to those projectiles either in the bore or during the flight. Is your twist rate fast enough to stabilize those bullets? Any sign of keyholing or slightly oblong holes in the target? Maybe an unstable bullet would lose its efficiency? Just some thoughts. I'm interested to hear what you find. Keep us informed.
Rroehl108
New Member
With my experience with the 156 your bc is off. I have a verified G7 BC of .330. The .347 they post on the box is way high in my opinion. Not saying this will totally fix your problem but may get you closer.
BrentM
Well-Known Member
Doesn't seem like he's shooting far enough to be a truing issue tho. I ran a 156 out to 1500 last month at 2800 and it was dead on. Elevation was 5000 feet tho.
Rroehl108
New Member
My velocity is also similar to yours with that verified bc. I'm at 3018 fps and .330 bc
If I adjust for a corrected G7 BC of .330, assume a 100 zero (this could be a stability issue that resolved itself down range), use the standard atmospherics in the calculator and adjust the velocity to 3027, @ 800 yards I get a drop of 16.21. I am fairly certain that you have several data points that are incorrect.? Your real world observable data is correct but multiple inputs into the calculator are not.
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DDWing
Well-Known Member
I just experienced this very same problem with Strelok. The only way I could make anything line up correctly was to drop my MV by 280 fps.
Thanks, I've always adjusted the velocity on the bullet page not realizing that was even a function. Learned something new todayā¦again, thank you!
What is the scope height above the bore? That is important. I too thought I had "cant" under control until I permanently installed a level on the scope. Adding the level made a world of difference past 500yds.
Were you feeding the ammo out of an internal magazine? If so try again feeding rounds one at a time by hand.
I have a Cooper model 52 Classic in .270wby mag. In a shooting session using hand loads that I knew were tack drivers. Here are the velocities I recorded for five 5-shot strings fed from the magazine in the order of firing. Firing from a shaded shooting position, 63F with no wind. Allowing 10 minutes between shots with the bolt open to cool down.
I was using 71.9gr IMR7828 CCI Large Rifle mag primers, Swift Sciroccos 150gr. I believe that at the time Norma was making the brass for
Weatherby.
1. 3340, 3345, 3351, 3375, 3418
2. 3335, 3348, 3357, 3373, 3424
3. 3337, 3347, 3359, 3378, 3431
4. 3342, 3344, 3366, 3382, 3404
5. 3343, 3348, 3361, 3382, 3416
This test resulted in commensurate changes in POI and group size.
The next five 5-shot string data set was hand fed one round at a time.
1. 3340, 3345, 3351, 3342, 3333
2. 3338, 3348, 3340, 3348, 3334
3. 3332, 3347, 3339, 3333, 3431
4. 3338, 3344, 3336, 3342, 3334
5. 3343, 3338, 3341, 3352, 3336
Grouping was less than 1moa at 200yds.
Looking closely at the data you'll see that in the first group each shot of each string is continually increasing
Each shot in the second group moves around with a very reasonable ES and Mean which did show itself in
the on target performance.
I again started a five 5-shot test feeding from the magazine. I measured the OAL of each round and recorded them in the order I put them in the magazine. This time I fired a round. Then pulled each round out of the
magazine and measured each one with a dial micrometer and recorded the lengths in the order they were removed from the magazine.
Then I put them back in the magazine in reverse order, fired another round and measured again until all 5 rounds had been fired.
I quickly found that rounds that were all the same OAL when I started were getting progressively shorter with each shot. Recoil was moving the rounds in the magazine driving the bullets against the front of the magazine and back into the case. This caused the internal volume of the case to be changing with each shot. The lessening volume increased pressure increasing velocity. These were 3x fired cases. I had not previously crimped but let friction do its job. From then on I annealed and crimped. I've seen this on a number of calibers with stout recoil. The .270wby mag is a belted magnum.
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Just my opinion, but you have a 60 fps extreme spread listed. For me, that's too much and would mean doing some load tuning. A single digit SD is necessary for precision shooting, imo
Go with what's physical evidence...what's shot....make the zero correction....call it a day! Too often this question is asked...always must be something terribly wrong....they are apps...they offer great starting points...GREAT ADVICE...but as we know....every load works differently in every gun...every gun works differently...ten guns all identical ( if that's possible) ....ten bullets...all identical....maybe only a minor difference...maybe large....the app can't account for every personal weapon...what is...is....make the simple correction to real world (truing function)....and shoot happily ever after! There doesn't have to be....WHAT'S WRONG!...Just go with WHAT IS!
