Ballistic Calculator / Chrono Inaccuracies

[hunt1up]

First things first, I'm no competition shooter or gun guru. But I know how to shoot rifles pretty well at reasonable distances(out to 500-600 yards) and I feel like I have a decent undestanding of what's what.

Over the past 2 years I've sighted in 4 guns with scopes for dialing or holdover. Two Zeiss V4s, a Leupold VX3, and the latest a Swarovski Z3 with BRH reticle. On every gun, the real world results vary from what ballistic calculators stated. I've used Strelok, Hornady's calculator, and for the Swaro scope I used their calculator for my BRH drops. I've inputted correct bore height, elevation, etc. I'd estimate on the dialing scopes they've been off by .25-.5moa. With the Swaro scope this week my POI is off by about 30 yards for every holdover mark. For example, first hash shows 204 yards in the calculator but in the real world I'm dead on at 175 yards. All these guns shoot very well and once I get things figured out they're damn near perfect. It's just getting to that point that's been a bit annoying.

I've poked around other threads on this topic and the one variable I've come down to is my chrono. I have a Competition Electronics ProChrono DLX. I've used it on arrows, crossbow bolts, ML loads, and rifle loads. The results always seem like they're close to what they should be. Perhaps this thing isn't as accurate as I thought? Could I be seeing enough inaccuracy in its numbers to be the culprit? What might be the "best" chrono out there to consider? Any other thoughts?

 

[Bluefish]

Are you using Hornady 4dof or the conventional calculator? There is built in error using a single BC to calculate drop. Simple answer is BC varies during flight and is not a static number. If having issues with 4dof, then I would look at your chronograph.

competition electronics makes pretty good stuff imho.

 

[Hoosker Doo]

Make sure your point of impact is dead on at 100 yds. I was doing the same thing but my zero was about 1/2 moa high (touching the top of the bullseye), which then turns into 2 MOA high at 400 yds.
I did also estimate my actual velocity to be a bit different than what my chronograph measured after shooting groups at distance and observing the drop.

 

[SoTxShooter]

Make sure your point of impact is dead on at 100 yds. I was doing the same thing but my zero was about 1/2 moa high (touching the top of the bullseye), which then turns into 2 MOA high at 400 yds.

Definitely check this, as I also learned the hard way!

In general, my experiences are the same as yours. That is why I never rely on the chrono as gospel. It's a great way for me to find a ballpark starting point, but at distance, I let the target tell me what's going on and I'll adjust my dope and drop charts based on that alone. I've never had a rifle to where the chrono, ballistic calculator, and target all read the same thing.

 

[hunt1up]

Thanks guys. Simply checking for exact zero at 100 yards might be the culprit here. I've been guilty of being ok with 1/2" high when sighting in a deer gun or other point and shoot weapons. So I certainly need to check that going forward.

 

[rayporter]

has anyone ever proven beyond a doubt that the chrony was off by a significant amount?

i have known of 2 guys that thought the chrono was bad and went to great lengths to find that it was good.

 

[hunt1up]

has anyone ever proven beyond a doubt that the chrony was off by a significant amount?

i have known of 2 guys that thought the chrono was bad and went to great lengths to find that it was good.

My gut is that the chrono is probably pretty close. The numbers are relatively close to stated velocities on factory ammo, with some expected variation for barrel length and such.

 

[Laelkhunter]

Make sure your projectile BC is accurate. That might be the culprit.

 

[eric1115]

Make sure your projectile BC is accurate. That might be the culprit.

No, this is incorrect. There is zero chance an inaccurate BC is causing misses that large at that range. Very few shooters (myself included) have any business trying to true BC at all, as most of us can't shoot well enough at the 1000+ yards needed to generate meaningful data. Nobody needs to true BC at a few hundred.

 

[Laelkhunter]

I didn't mean anything about "true BC". I was just suggesting that he might want to verify the BC of his bullet. Since he didn't mention the bullet he was using or the BC for his calculations, I thought it was a good thing to check. You are correct that at the ranges he is shooting, a miscalculation of .020 or .030 won't make a difference, but if he misplaced a 4 for a 2 in the .4 or .2, it might alter the trajectory just a little.

 

[hunt1up]

I've definitely verified the factory listed BC for any rounds I've fired. It'll be a little bit before I meddle with sighting in another gun since hunting season is upon us and all my stuff is sighted in. When it's time to sight in the next one, which won't be far off, I'll take everyone's recommendations into account. I appreciate it!

 

[eric1115]

I didn't mean anything about "true BC". I was just suggesting that he might want to verify the BC of his bullet. Since he didn't mention the bullet he was using or the BC for his calculations, I thought it was a good thing to check. You are correct that at the ranges he is shooting, a miscalculation of .020 or .030 won't make a difference, but if he misplaced a 4 for a 2 in the .4 or .2, it might alter the trajectory just a little.

Gotcha. My apologies for misreading your intent. Thanks for clarifying.

For anyone thinking of truing BC at shorter ranges, a 400 yard shot going from a .530 G1 to a .600 G1 yields a difference of about .5" (0.17 MOA) with a set of reasonable environmental and load inputs.

 

[LaHunter]

Strelok has been very accurate for me out to 800 yards. It matches my Kestrek 5700 with AB within .1 MOA. There could be issues with your scope(s) not dialing exactly ‘true’ also. If all of your inputs are correct, Strelok should give you a good solution. It is common to need to ‘true’ your muzzle velocity with any app by maybe 1-2%.

 

[Laelkhunter]

......There could be issues with your scope(s) not dialing exactly ‘true’ also. If all of your inputs are correct, Strelok should give you a good solution. .

I am thinking along these lines also. Possible the Z3 is not tracking properly? I have a Z5, and bought it because Swaro uses 4 coil springs to support the erector assembly where the Z3 only uses one leaf spring.

 

[hunt1up]

I am thinking along these lines also. Possible the Z3 is not tracking properly? I have a Z5, and bought it because Swaro uses 4 coil springs to support the erector assembly where the Z3 only uses one leaf spring.

This Z3 is a BRH reticle and doesn't dial. Just a holdover reticle. The swarovski ballistic calculator was somewhat off on that one as well.

 

[Laelkhunter]

This Z3 is a BRH reticle and doesn't dial. Just a holdover reticle. The swarovski ballistic calculator was somewhat off on that one as well.

I have the BRH in my Z5. What I meant was if you are dialing for yardage as opposed to using the BRH reticle (which you have to turn up to 18x for the reticle hash marks to be accurate). Good luck in finding your solution to your problem. Hopefully someone can help.

 

[prairieboy]

my cheap shooting chrony could not be trusted after a few years. it said everything was 200 fps give or take slow.

 

[Highvoltage1]

I’ve literally put 2 chronographs back to back and seen significant deviation between them.I rarely use one anymore. I shoot my drops out to 600 and play with the velocity in the bc calculator until everything lines up. I’m not sure this is the correct method but it works for me. Best wishes

 

[Mike Islander]

Does it matter? True your calculator by adjusting velocity until it matches your POI. You are going to confirm at short to long range anyway, right? Once it matches, then it's useful?

 

[hunt1up]

Does it matter? True your calculator by adjusting velocity until it matches your POI. You are going to confirm at short to long range anyway, right? Once it matches, then it's useful?

Fair point. In the end it doesn't matter so long as the gun shoots where it's supposed to at the distances I need it to I suppose. I was just curious if there was something missing in getting from point A to point B.