First let’s describe what I’m shooting and where. I only have 200yds to playwith at this particular range which is less than 100’ above sea level. , Rem 700 22", sight height 2.7", barrel 1/10 twist, 168gn BTHP @ 2650fps. The Bergers ballistic caslculator shows a drop of 2.03" @ 200yds when zeroed at 100yds. My actual results at 200yds is .5" high @ 200yds. What am I missing?
Is the sight height over bore correct? Center of barrel to center of scope. Is your velocity measured or what is printed on the ammo box? Is it a zero MOA scope base or 20 MOA scope base?
Did you chrono? Playing with my calculator I can’t find any combo that zeros 100 and is higher at 200 with a velocity anywhere near your numbers. To really exaggerate things I had to raise scope height to 3.75" and upped velocity 3500 with a HPBT 168 (SGK) to get .5" high at 200, using my calculator.
There is such a thing as a primary and secondary zero, as in you actually/ accidently hit on the secondary zero where the bullet is still climbing relative to the sight at 100 yards. Never heard of it applied at 100 yards with a large rifle cartridge. Don’t even know if possible.
Wouldn’t even know where to begin, but something to check into after exhausting all other more common possibilities.
No. The box of factory ammo (Hornady) claims 2700fps and I think that was calculated with a 24" barrell so I figured 2" shorter barrel would be about 50fps slower in the shorter barrel. I measured the sight height from the scope ring mating surface to the approximate barrel centerline and got 2.7".
I will chrono next time with the same ammo and at a higher altitude.
Something funny going on for sure. What scope do you have? Did you go back and confirm 100 yard zero after the +0.5" at 200 yard shots? How many rounds do you fire for each range?
Vortex Strike Eagle and yes I did confirm the 100yd zero. three shots each.
Doing everything right and getting wrong results!
Wonder what would happen going backwards, sighting in -2.03 at 200 and then shoot a group at 100. Or like I do, zero at 200 and see what 100 looks like.
Just out of curiosity, what do your 200 yard group look like?
Less than .5" @200 and .375 @100 and it’s repeatable.
Also shooting from prone with harris bipod and no rear bag.
By the way it’s a 308.
Assumed 308. That grouping is better then I get with my handloads in my 18" AR 308 off a bench. Just puzzling how you end up so far off the ballistic table.
I think is has a lot to do with scope height vs the apex of the arch of flight.
if the 100yd mark was the apex then their ballistic charts are correct.
I think I should put targets out at 175yds, 200yds, 225 yds and 250yds to find the apex of the trajectory.
Next sunday I plan to shoot at the Clinton House 300yd range to check thom out before I get a membership to gain access to their 1k yd range, it’s a two hour drive but I think it might be worth it.
As @shooterrex mentioned the sight height from center of barrel to the center of the reticle of the scope may be different also look at the test information is the barrel shorter that yours. If you are shooting a longer barrel is will generate faster fps and stabilize the bullet more and thus utilize more gases from the powder giving more rise to your bullet trajectory. But with a 22" barrel it throws me some as i could see it from a 24 or 26" barrel. I watch Ron Spomer shooting with 308 rounds from winchester and was consistently getting 50-100fps more than advertised.
Edit? Just thought of this . How close is your bullet to the lands ? If it is really close you may be getting more pressure ??? Maybe Im wrong on that. And also just caught were you said your barrel was shorter. It aint adding up for me for sure.
It’s not just a little bit either. That is a huge difference from what the ballistic calculator shows. Not just a few fps or a little off on the scope height. Like the scope gets dialed up (down?) 10 clicks.
Yeah i will probably study on this in my sleep . That is significant
What is the reticle view in that eagle scope ? Ballistic plex? @DurangoDave
Also how new is this scope set up to you ?
I once shot a H&R handi rifle with a high scope mount . It was a youth model. The young shooter was shooting with a check rest. I was consistantly hitting 3" different than the youth was. I cant quite explain it . But the youth could bullseye it and I would be 3"low. I determined (again may not have even been correct but) that it was the size of my head from my eye to my check was longer. could it be something like that .? I believe @albroswift is on to something. The chronograph wiĺ tell you akot especially is the Standard Deviation is small and the Extreme spread is small.
Tho I use a 30-06 and 178gr A-Max. I always set my zero at 200 yards.
That way I can go out to 735 yards without twisting a dial.
Chrony is the only way. In the 60s my ole man and his WWII buds all used slide rules and ballistic charts to get out past 600 yards.