Help w/ Ballistics Calculation

[imyomama]

It’s also amazing that people make arrogant comments like that with zero need to do so. Point of fact….if anything, this rifle’s muzzle velocity is slower than the published FPS which would actually increase the elevation dope. I think we can all agree on that. As stated in my original post, I’m using the G1 of .372. The issue was that the elevation dope I ended up using was for a bullet traveling well over 3000 FPS which we know is nowhere near accurate. Whether I had a chronograph or not, it wouldn’t explain why 9.25 MOA come up worked for 500 yards. I appreciate the help, but the extra comments aren’t necessary. It seems to me that those saying the scope may have tracking issues must be correct. Even if the sight height was entered incorrectly as 3 inches, that still wouldn’t get it anywhere near the 9.25 MOA come up. I simply didn’t think about the scope tracking after all the positive reviews on the Arken tracking. The glass is by no means German or good Japanese glass but the tracking has seemed to be great.

apparently , if you did something wrong, pointing it out will be arrogant..
so i'll go with pure f@#ing magic so everyone can be happy .

[PVDT]

apparently , if you did something wrong, pointing it out will be arrogant..
so i'll go with pure f@#ing magic so everyone can be happy .

Apparently you must be a lot “smarter” than the rest of us. The point being made was that a chronograph would be absolutely ZERO help since the dope used to hit at 500 matched a bullet that’s 15 grains lighter than the actual bullet shot. Having a chronograph night change the dope by .25-.5 MOA max…not nearly 2 MOA. But since you and the other fella can’t comprehend that, let’s simply close the thread. This is social media at its finest. Might as well be FB.

[PVDT]

I’d do a tracking test first for sure. If the scope isn’t proven, need to get that handled first and foremost. I usually do mine at 200yds. Have a target that’s at least 4ft top to bottom, the bigger the better. I test mine at least 5moa up/down/left/right and it should all come back to zero at the end.

Past that, I’m not wise enough to know what the issue could be. Before I got a chrono I just went off the listed muzzle velocity for my calculations, and then adjusted the velocity input up/down until it matched what I was seeing on paper for 2/3/400yds. So a chrono isn’t a MUST when you have all the other data available, but is definitely the best option.

I appreciate the genuine feedback. Thanks. I did a tall target test today and the scope tracked absolutely perfectly. I shot a group, dialed up 32 MOA, and the middle of the next group hit exactly 33.5” above the first. 32 MOA would be 33.504” so the scope is dead on. I also checked my yardage where I shot the target. This time I came up with 506 yards but that wouldn't come close to the nearly 2 MOA error. I have no clue.

[Cajun Blake]

Past that, I’m not wise enough to know what the issue could be. Before I got a chrono I just went off the listed muzzle velocity for my calculations, and then adjusted the velocity input up/down until it matched what I was seeing on paper for 2/3/400yds. So a chrono isn’t a MUST when you have all the other data available, but is definitely the best option.

how many total shots does it take you at 200, 300, 400, yds to calculate the velocity ? 10, 15, 20+ shots ? What if your bullet or group fired is affected by wind, mirage, poor bench technique, etc... ?

With a chronograph, it only takes you 1 shot to record the velocity. Shoot 3 ~ 5 rds. and get the average fps including ES and SD. Plug that data into your ballistic app and you're done, no more second guessing click adjustments.

[Raider4044]

I’m kind of baffled now that it seems the scope is tracking true. It’s definitely not ideal shooting without a chrono, but not as big of a deal as others are making it out to be. Like you’ve said, you’re not far enough off on your velocity to cause that much of a change in elevation.

I hate to ask, but have you double checked your zero at 100?




This won’t make a huge difference either, but go ahead and get an accurate scope height measurement. An AR will definitely be higher than 1.5”.

[bearintex]

I appreciate the genuine feedback. Thanks. I did a tall target test today and the scope tracked absolutely perfectly. I shot a group, dialed up 32 MOA, and the middle of the next group hit exactly 33.5” above the first. 32 MOA would be 33.504” so the scope is dead on. I also checked my yardage where I shot the target. This time I came up with 506 yards but that wouldn't come close to the nearly 2 MOA error. I have no clue.

That complicates things. Where are you located? I bet there is someone nearby with a chrono.....

Are you absolutely sure of the BC? Some bullets list different BC's based on velocity. I assume you're in Texas so your atmospherics shouldn't come too much into play. You have checked those in the app? The apps are only as good as the data you feed them.

Good to hear the Arken tracks well. I've heard nothing but good about them. I'm waiting for a LVPO from them or Athlon.

[PVDT]

I’m kind of baffled now that it seems the scope is tracking true. It’s definitely not ideal shooting without a chrono, but not as big of a deal as others are making it out to be. Like you’ve said, you’re not far enough off on your velocity to cause that much of a change in elevation.

I hate to ask, but have you double checked your zero at 100?




This won’t make a huge difference either, but go ahead and get an accurate scope height measurement. An AR will definitely be higher than 1.5”.

I did check my zero and it’s still a half inch group covering the bullseye. And I also checked all the torque on everything. I do have a chronograph on the way because I have other guns I want to get ballistic data on and it will obviously make it a lot easier….as others have said. The only thing I can figure out is my dumb$$$ just dialed the dope incorrectly. I do have screenshots of my settings in the Hornady app but I can’t post pics.

[ORIONTHEHUNTER]

Bad info in equals bad info out. Velocity discrepancies can affect more than .5 moa. If your shooting factory ammo its amazing how one box can have varying powder amounts, COAL, seating depths, and other issues. Not to mention the differences from box to box even within the same brand of ammo. Sorry you took my post personal, but chronographing your rifle and loads is one of the first steps of getting accurate data.

[PVDT]

Bad info in equals bad info out. Velocity discrepancies can affect more than .5 moa. If your shooting factory ammo its amazing how one box can have varying powder amounts, COAL, seating depths, and other issues. Not to mention the differences from box to box even within the same brand of ammo. Sorry you took my post personal, but chronographing your rifle and loads is one of the first steps of getting accurate data.

I did take it the wrong way and I apologize. I did order a chronograph so time will tell. I think I’ll find that the data I used was “close” but human error was the cause when I dialed the dope. There’s simply no possible way the data is far enough off to miss that high at 500. Heck you can change the variables in 4DOF and see that within a few minutes…at least that’s what I’ve seen. Someone mentioned if I was using the correct G1 BC…..I’m using .372 that I got directly from IMI’s website. So surely that’s not it. I have 5 different ballistics apps and have confirmed all my data is correct including using G1 and not G7. Hopefully the weather gets better early next week and I’ll see what happens with the chronograph.

[BrianL]

My first WAG is scope isn't tracking at true MOA per "x" clicks.

[trophy8]

Some of that IMI stuff runs HOT too. As stated, a chrono should solve a lot of headaches even if that wasn’t the case here. You’d be shocked how fast some of that ammo will run in a 16” barrel.

[db@100]

If you have your dope from 100 to 500 yards, what difference will chronograph make?
Isn't your dope, your dope?

[PVDT]

Well as I suspected (on two points), the chronograph was zero help. I was using 2727fps as I stated in my original post. With the chronograph, I learned the average speed is 2725 with the IMI 77 grain (2728, 2745, 2735, 2712, 2709). So all the talk about needing the chrono to fix this particular problem was as I figured unnecessary. HOWEVER, I’m certainly glad I got it because it helped me get my speeds on 3 other rifles that I wasn’t too sure about in my ballistic settings. The IMI 77 grain speed I knew was very close because I’ve seen the speeds out of a few different rifles the same as my setup. But……on point #2…..I did have a hall of fame worthy dumb-$$ moment. I went out and confirmed with the chronograph that my speed was good (or close). So I changed my FPS and came up with nearly the same dope. Obviously. Then I confirmed my 500 yard target and CORRECTLY dialed 12.25 come up. And what do you know….it hit the target 2 inches high. Bingo. My dumb butt simply dialed the dope incorrectly! So whenever y’all need me to waste a little of your time, give me a shout. Thanks to everyone for trying to give me a hand.

[tdwinklr]

A chrony is never a bad thing to have. Glad you got it figured out.

[bearintex]

Leave your velocity as the chronograph tells you and play with the BC to get it to match. Could be inaccurate information from the manf about the bullet.