Something weird happens between 800 and 1,000 yards

Jul 14, 2011
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Louisiana
#1
Good Afternoon all,
I'm fairly new to any type of LR shooting, and I'm shooting a rifle that a ton of other new shooters are using: SPS Tactical in .308. Today I was confirming my dope compared to my predictions on BallisticsARC. At 800 yards, I had to make a correction of .4 mils up to hit the approximately 8" orange spray painted circle on steel. I used the truing feature on BallisticsARC and it adjusted my velocity from 2644.6 to 2607.5. Now when I go back to 1,000 yards my original velocity is what I need to use in order to get hits. For conditions like today, I know I need to dial up .4 for 800 but what about other days when there's a huge difference in the environmental conditions?

Am I just asking too much from this rifle or is there a way to consistently account for whatever weirdness happens around transonic velocity?

Ammo is 168gr. ELD-M, 45.5 of Varget, Prime brass and CCI BR2 primers. The rifle is the 1/12" twist version, in a Manners EH1-A w/ mini chassis.

Thanks
 

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#2
True the computer to the rifle, not the rifle to the computer.

Dope the rifle first, record and confirm the conditions including the range. The 800-yard target could be off, then when shooting on steel instead of a circle, use a straight "Watermark" to confirm the elevation is either on the line or less than a click off, either high or low.

When truing leave the computer alone until after you finished gathering data.

Last, did you check your scope, there may be a spot in there that does not adjust correctly. The scope has to be calibrated and tested it's the weakest link in the system next to the shooter. If you have not calibrated the scope across 100% of your travel, everything you posted is meaningless from a control standpoint. The scope could have an issue, minor of course, but still something. You are dialing up 24MOA or so, 6 MILs give or take, that is enough for errors to show in the travel.

Focus on the shooting and worry about the computer after you have gathered your data. Things tend to work better that way.
 
Likes: stereo.pete
Jul 14, 2011
87
34
18
37
Louisiana
#3
Thank you, Frank!

Admittedly, the only calibration I've done is some type of tall target test at 100 yards. I had two dots 36" apart vertically. I shot the lower one with my 100 yard zero, dialed 10mils up and fired at it again then checked my second impact in relation to the upper dot. I don't even remember the measurement (it was REALLY close), or where I found that test. I did not check any adjustments in between...
 
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