Help w/ Ballistics Calculation

[PVDT]

I’m having difficulty finding the incorrect value in my calculations. I’m shooting a Savage AR15 223. The ammo is IMI Razorcore 77 grain SMK with a .372 G1. I don’t have a chronograph but have seen videos showing 2727 FPS out of a 16” barrel. So I use 2727 for the muzzle velocity. At 500 yards, the elevation shows to be 12.16 come up. But when I shoot it’s very high. I dialed down to 9.25 come up and shot a 4 inch group at 500. Nearly 2 MOA is a significant difference in the dope at 500 yards. Heck, if 9.25 is correct, that would put muzzle velocity over 3000 FPS which we know isn’t correct for the 77 grain. The published velocity is 2740. Does anyone know what the problem could be?

[sticknstring]

Sounds to me like you haven’t “computed” in your scope height. More than likely your scope is set higher than the info you are getting from your ballistics chart. Make sure your scope height is compatible to the chart/ info you are using

[ORIONTHEHUNTER]

You need to calculate your scope height like has been mentioned. You also need to chronograph your rifle to get your exact FPS.

[PVDT]

The scope height is set at 1.5”. I just used that by default. Even if it’s 2 inches, that would only change the come up slightly at 500 yards and nowhere close to the nearly 2 MOA I’m off. I now wonder if somehow I ranged the yardage incorrectly….somehow. When I shoot different yardages, I move to another area of the farm and move the target to whatever yardage I want to shoot (the topography is perfect for it). Do you guys come up with the same come up as my 12.16 plus or minus a little. If so, I must have messed up on ranging the target.

[howabouttheiris]

Yes. I come up with similar numbers.

Is your scope zero at 100 yards? A 50 yard zero will put a good portion of that error in.

[PVDT]

Yes. I come up with similar numbers.

Is your scope zero at 100 yards? A 50 yard zero will put a good portion of that error in.

It’s 100

[ORIONTHEHUNTER]

Either your velocities are off because you didn't chronograph or your scope isn't tracking properly.

[Raider4044]

What scope are you running? Sounds like it may not be tracking correctly.

[bearintex]

I say a compounding of errors. Scope height, velocity, BC, and (probably primarily) scope tracking.

Get the numbers right in the calculator and do a tall target test and get back to us.

What calculator are you using? I’ve found the Hornady 4DOF to be dang near perfect with everything I’ve put in it.

[TxxAgg]

Shoot 20 rounds at 100 and find your true zero

I shoot the 77 gr TMK's out of my 16" T3x at 2605fps. I dial 12.5 MOA at 500 yds.

[PVDT]

I say a compounding of errors. Scope height, velocity, BC, and (probably primarily) scope tracking.

Get the numbers right in the calculator and do a tall target test and get back to us.

What calculator are you using? I’ve found the Hornady 4DOF to be dang near perfect with everything I’ve put in it.

I’m using the Arken SH4 6-24x50. I am actually using the Hornady 4DOF.

[Cajun Blake]

IMO, a chronograph is the single most important tool when reloading, shooting for accuracy, and trying to find your long-range dope.

Without a chrono you're wasting your time. A barrel will have certain "accuracy nodes" that are based on velocity. Your barrel might shoot a 1-hole group at 2750 fps, BUT it could become a 1" group at 2650 fps.

buy a $200-300 chrono and it will make your shooting life so much easier. Many times the velocity printed on the side of a box of factory ammo is not even close to real world shooting conditions.

[ORIONTHEHUNTER]

It's amazing people would try to shoot long range and not chronograph their rifle and loads. Also are you using a g1 or g7 ballistic coefficient in your program?

[PVDT]

It's amazing people would try to shoot long range and not chronograph their rifle and loads. Also are you using a g1 or g7 ballistic coefficient in your program?

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.

[Chase4556]

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.