Bullet Drop Chart ??s

[dihardhunter]

Debated on whether this was more appropriate for the Firearms or Long Range subforum, went with this one only because I figured more guys are using drop chart apps and such...any help is appreciated.

Broke in a 6.5 Creedmoor, limited issue Browning X-bolt Stalker 26" barrel past couple weekends w/ 140 gr. match grade. This weekend transitioned to 143 eld-x for past 20 rounds or so of dialing in my zero and putting the chronograph to use. Zeroed at 100 yards, easily sub 0.5 MOA - cutting same bullet holes with nearly every round at that range with the eld-x's. Advertised BC is 0.625. I took average of 3 chronograph shots and getting 75 FPS more than box advertises at 2,775 FPS. At this stage, the gun is shooting BETTER than I had hoped.

(Scope I'm working with is SWFA 3-15x in MRADs if that matters to anyone, checked tracking and everything seems perfectly responsive.)

Anyways, punched all that info into Strelok and walked out to 2, then 300 yards. Groups expanded a little, still sub-MOA...chalk that up to operator error - never claimed to be a dead eye, BUT the more concerning thing was that my bullets were consistently falling further and further below the bull. Needed another click at least at 200 yards and 2+ extra clicks to make dead nuts at 300 yards. Obviously the discrepancy is going to exaggerate the further out I go. Again working in MRADs. Worked backwards at the end of the session to drop 1 round in at 100 yards, and punched the dead center of the bull - so it's not a bumped zero I'm dealing with.



Put this chart together to show what Strelok says should be happening with drop trajectory according to my input, then played with numbers to adjust FPS all the way down to 2575 (which is 200 FPS lower than what my rifle is actually spitting out rounds) to do my best at replicating the drop I was observing in the field. Hated to do that but wasn't sure what else to do. By experimenting, it seemed the FPS factor was the easiest to adjust and see a measurable response in the app output, as opposed to tweaking the BC or scope height, etc. Not sure how this new (faked to mimic reality) output will hold up at 400 or 500 yards and beyond, but the difference between what my load should be doing and what I'm seeing off the bench are the difference of an entire kill zone at 500 yards - nearly 10". Blue is Strelok's (and a couple other apps I cross-checked) and orange is the reality I'm experiencing.

I've triple checked my input data from scope height to FPS to BC to anything I can think of, but this is sort of new territory for me. Any advice or guidance from those more experienced. Thanks in advance.

 

[whiskeysierra762]

Most BC's are exaggerated, but Hornady is usually pretty good with them.
I input factory BC (or BC from Litz's book Applied Ballistics) and then tweak the muzzle velocity in my ballistic computer until it gives me a chart that matches my real world come ups.
Run a box test on your scope to make sure its adjustments are correct. Just because it comes back to zero doesn't mean that its adjusting in correct increments.

 

[mt100gr.]

What chronograph do you have? I had a very similar issue when shooting "drops" at a tall target and had to adjust velocity by quite a bit. There's only one reason you'd be impacting low at longer ranges if all other inputs are correct and your scope is tracking.

 

[dihardhunter]

Thanks for the responses already.

Pardon the ignorance though...when you say "box test"? What do you mean?

Also, not sure on the chronograph make/model? It did give a reading every shot though and put cardboard with target up at 20 yards to shoot same bullet hole/trajectory through chrono to ensure consistency.

 

[ckleeves]

I would shoot a tall target at various distances (200,300,400 to as far out as the target size will allow) without putting any adjustment on your turrets then measure your drops to make sure your scope is tracking perfectly true.

 

[wind gypsy]

http://bulletin.accurateshooter.com/2015/11/calibrate-your-clicks-with-tall-target-test/

^ how to validate your scope is tracking.

 

[dihardhunter]

Thanks everyone, that's what I'll try.

 

[danmayland]

I agree with the above posts. It's probably a likely chronograph error. If your shooting in direct sunlight vs shade your chrony readings can be greatly affected. Shooting with the chrony in the shade is preferred. Unless of course it's a Lab Radar or Magnetospeed. Set your scope turret to your 100 yard zero. Then take a 4' piece of butcher paper and put a shoot-and-see 3" dot at the top. Place one at 300 yards, 400 yards, 500 yards all the way out to your expected shooting distance. Obviously you will need longer paper for any distance that is going to result in a bullet drop greater than 4'. Shoot a 3-4 shot group at each distance aiming at the Shoot and see dot. Then measure from center of the dot to the center of your group. This will give you your "actual drop" data. Any good app will allow you to modify your dope using verified drop data. You don't even need a chrony.


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[Jesse Jaymes]

Welcome to the most maddening portion of trying to stretch the legs of your shooting and equipment. I struggle with the exact same issues. Or have. I won't chime in on a guaranteed fix. And you'll most likely become further frustrated, as you've stated you've kinda checked scope tracking. I personally don't think that's the issue at all, but I am not the smartest one on here.

Sometimes it takes a bit of digging to find out the manufacturer's exact value for each click. I shoot MOA and there was a vast difference in the MOA value Vortex used. I believe it's Shooter MOA vs Actual MOA. .995 vs 1.04

My guess is it's the data input into your program. Or it's a flicked or unflicked toggle on the Ap. Do the best you can to gather as much data as possible when you zero. Atmospheric conditions. Baro. Humidity. Things like Temp Sensitivity in the program can make differences in your solution data. You've done well getting some Chrono speeds. That should get you very close. You can scrub or add 20-50fps to true...but as you've stated....you are several hundred FPS off in order to match the POI. That's not right. Your chrono'd speeds seem reasonable given your 26" tube. And I think Hornady does a pretty decent job of making true spec ammo and the listed FPS should be close.

Maybe post as much data as you can and see if someone will run your solution for you and see if your come ups at 800 yards match their numbers/solution?

 

[mt100gr.]

^^^ post your data , as much as you can, and someone can run it through AB. I was using strelok pro for awhile and the exact same data gives different come ups in AB. I wanted to believe the AB corrections but the shooting matched strelok....I was set straight by a tall target and biting my lip as I reduced the velocity input. Now my corrections from AB are spot on and I just have to trust that gravity is more accurate than my chrono. I badly wanted that speed number but it's just not the case.

 

[Hiwayman92]

I have found strelok to have large discrepancies over Shooter or the Applied Ballistics App. Try one of them, or the huskemaw or longeangehunting.com calculator. From my recollection strelok does not account for barrel twist or other variables like the better programs do.


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