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#6407891 - 08/14/16 03:44 PM Ballistic Help
hookemhorns Offline
Tracker

Registered: 01/10/06
Posts: 639
Loc: Forney, TX
I have a Tikka CTR 308. I switched ammo to a Nosler 165grain Accubond. After 3 shots I was zeroed at 200 yards. Shot 4 another bullseye. The conditions are 85 degrees 70% humidity, 7-10 mph wind directly into my face and I am shooting off sandbags.

Let's go to to 300 yards.
My Ballistic app says I should be at .7 Mils, (7.6 inches)

First 2 shots 15-16 inches low with .7 mil adjustment. I thought I must have taken bad shots.

Shots 3-4 still way low. Make adjustments.

Shots 5-6. 1.5 mil adjustments with wind gusting a little stronger in my face. And I am still low.

Any suggestions, ideas or information on why this much adjustments?
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#6407894 - 08/14/16 03:52 PM Re: Ballistic Help [Re: hookemhorns]
papa45 Offline
Bird Dog

Registered: 05/14/07
Posts: 486
Loc: Arlington
Could be a problem with the scope???

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#6407923 - 08/14/16 04:12 PM Re: Ballistic Help [Re: hookemhorns]
bo323 Offline
Tracker

Registered: 09/24/11
Posts: 708
Loc: Snyder, tx
Check all your screws first. If nothing is loose, try sitting your gun on a lead sled or sandbags. while aiming at a target, try adjusting your scope to see if the rosshairs move.

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#6407961 - 08/14/16 04:44 PM Re: Ballistic Help [Re: hookemhorns]
603Country Offline
THF Trophy Hunter

Registered: 07/03/12
Posts: 5039
Loc: Central Texas
What's your bullet speed? If you haven't checked it, could be it's slower than you think. And yes, could be the scope. I've had more than one fail.


Edited by 603Country (08/14/16 04:46 PM)

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#6407990 - 08/14/16 05:09 PM Re: Ballistic Help [Re: hookemhorns]
Cleric Offline
Veteran Tracker

Registered: 03/11/12
Posts: 2618
I doubt if it would adjust to 200 and be on with a screw problem. I am going turret issue. I would shoot a dot pattern to make sure it adjusts right. I.e. Adjust 1 mil and make sure the poi moves the right distance. Do it in all 4 directions.

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#6407991 - 08/14/16 05:10 PM Re: Ballistic Help [Re: hookemhorns]
Texas buckeye Offline
Veteran Tracker

Registered: 11/22/11
Posts: 3089
Loc: Keller
Couple of things to think of real quickly, wind in the face will slow a bullet down, wouldn't expect it to do that much but maybe gusts are stronger than apparent?
Second, is there a possibility mirage is hurting your sight picture? It's hot out there and barrels heat quickly in this heat, so it's possible, but that would affect groups more you would think rather than just y axis.
Third, as mentioned above bullet speed is probably slower than you are getting ballistic data for. .308 tend to be shorter barreled guns, but this is just an assumption so that may not be anything.
Fourth, the ballistics calculator may be off. Did you double check with a different calculator?
Fifth, the range may be wrong on the distance. Did you double check that as well?

Just a couple quick things to check off.

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#6407995 - 08/14/16 05:11 PM Re: Ballistic Help [Re: hookemhorns]
Cleric Offline
Veteran Tracker

Registered: 03/11/12
Posts: 2618
Also the ctr has a 20 inch barrel and most manufactures use 24-26 so you will be slower than the box.

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#6407998 - 08/14/16 05:14 PM Re: Ballistic Help [Re: hookemhorns]
Dalee7892 Offline
Pro Tracker

Registered: 05/04/15
Posts: 1159
Loc: Denton County
Ok, probably start with shorter barrel- how does one determine what drop the 18 or 20" would have? More math or shoot more to know the rifle?

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#6408009 - 08/14/16 05:21 PM Re: Ballistic Help [Re: hookemhorns]
Cleric Offline
Veteran Tracker

Registered: 03/11/12
Posts: 2618
Use a chrono to Get the velocity to know for sure... The other way is to measure the drop at a know distance i.e. 100 yard to 200 yards is xx inches and put that into your calculator. The rule of thumb is 25 fps per inch

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#6408046 - 08/14/16 05:48 PM Re: Ballistic Help [Re: hookemhorns]
Texas buckeye Offline
Veteran Tracker

Registered: 11/22/11
Posts: 3089
Loc: Keller
Using gun data ballistics calc, adjusting 150ft/sec off for shorter barrel and giving a 15 mph headwind only have a drop at 300 of 9.4 inches, you are way over that (7ish with the .7mil adjust plus the 15-16 inches you shot low) at around 22-23 inches of drop. There has got to be something else going on than just the simple stuff....maybe.

Question: did you dial up instead of down, not paying attention to what you were doing? Although that wouldn't make sense since when you dialed more in (1.5mil) you were less low but still low.

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#6408054 - 08/14/16 05:56 PM Re: Ballistic Help [Re: hookemhorns]
FiremanJG Online   content
THF Celebrity

Registered: 12/16/08
Posts: 18144
Loc: Wolfe City, TX
What's your barrel length?
What scope are you using?

Typically the difference between 200 yards and 300 yards is in fact an additional .6 to 1.0 Mil.

You impacted low, saw the correction, and adjusted accordingly, and it was still low. I'm leaning toward the scope.
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#6409932 - 08/15/16 08:42 PM Re: Ballistic Help [Re: hookemhorns]
hookemhorns Offline
Tracker

Registered: 01/10/06
Posts: 639
Loc: Forney, TX
The CTR is a 20" barrel. I haven't shot through a Chrono so I don't know my actual speed.

For a little clarity when I said I was still low, when I adjusted scope it did adjust I was just still lower than I thought I should be.

The wind could have been stronger than I thought, it was hot and there was a lot of mirage.

I am using a SWFA SS 5x20x50

I am hoping to go shoot again on Saturday, but gotta find another place to shoot.
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#6409959 - 08/15/16 08:53 PM Re: Ballistic Help [Re: hookemhorns]
FiremanJG Online   content
THF Celebrity

Registered: 12/16/08
Posts: 18144
Loc: Wolfe City, TX
Excellent scope! So it was shooting consistently, but was lower than you thought it should be? There's an old saying "believe the bullet". If it's hitting consistently low, then lower your MV in your ballistic calculator until it matches.
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#6423684 - 08/25/16 08:00 AM Re: Ballistic Help [Re: hookemhorns]
onlysmith&wesson Online   content
Bird Dog

Registered: 07/10/14
Posts: 250
Loc: Lewisville/ Foard County
I have this identical rifle with a Vortex Viper. I don't have a chronograph and am really interested in learning what velocity you are getting. I'd appreciate a PM once you find out.

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#6423740 - 08/25/16 08:42 AM Re: Ballistic Help [Re: hookemhorns]
ImTheReasonDovesMourn Online   content
Pro Tracker

Registered: 08/04/12
Posts: 1054
Loc: Greenville, TX
You're probably running 2700ish with that bullet if it's a factory load.
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