My real world dope never matches the numbers my chronograph spits out. My optical always read much faster than reality so I bought a Magneto speed V3 and I get the same result. Both seem to read roughly 75fps faster than reality compared to multiple ballistic calculators. At least I know to subtract 75 and I’ll be close. Now to be fair, I think these things are good reloading tools as they at least read consistent and my single digit sd’s show on steel at distance so I can use it to weed out bad loads from the get go. Does anyone else experience something similar?
Chronographs suck
- Thread starter wade2big
- Start date
a bad zero easily explains this 99% of the time
My Chrono is dead on.
I insert the speed in my Kestrel with AB, using the custom curve, and my dope is always on.
I don't have to fuck with velocity or anything else janky to try and get my dope to line up.
I insert the speed in my Kestrel with AB, using the custom curve, and my dope is always on.
I don't have to fuck with velocity or anything else janky to try and get my dope to line up.
at 75fps that isn't the answer
I love mine it works you just need to know how to use it with a grain of salt . unless your one of those that can load shoot 20 rounds and get only one number for speeds and 1's for sd's , those that pick over every detail , nit pick each and every kernel and weight every primer . I just enjoy shooting and close enough is good enough for me almost 3 years and 8 different powders and we have kept speeds ruffly in or around the same speeds . sd change but taking an average it works out ok . best of luck to you getting along with your chrono , it's just a tool .
not 100y zero but 95y/105y or worse
.1-.2 high
parallax/scope issues
it can be a lot of things
If two different chronos (of different types) are giving you the same answer— that’s the answer. Much more likely the BC varies
so you tweak 500 and 750 to get 900 to match?
whats the tweak at 750?
what does a BC tweak at 900 give you for a result at 500?
what cartridge speed bullet?
I answered in post #14 but here it is in case you missed it.
It works. I just change the muzzle velocity to match my real world drop at 500, tweak it at 750 a bit and it lines up at the 900 yards that I have to shoot.
Very little at 750 and sometimes nothing at all. I just verify there if that makes sense. Today I added .2 at 500 yards (roughly 75 fps in velocity) and was dead nuts at 750. I didn’t shoot any further than that.
Yes. Thats correct on the Hornady 4dof I use. All of this really isn’t a big deal. I shot for a long while and never used a chrono. I would just do the exact same thing I’m doing now. Estimate muzzle velocity and shoot at a known distance (rangefinder) and then play with a calculator until it worked out to my real world numbers.
Maybe I need to play with the sensitivity settings on this thing considering everyone else’s seem to line up correctly.
Bingo. Because you get different results from what a program says does not mean it's a chrono issue. The chrono is only one part of the equation. Got to make sure your scope tracks 100% also. So don't scream chronos suck as that's just misplaced anger.
No anger my man. It was a catchy title for a thread and nothing more. I already said it was no biggie. I have my own personal 900 yard range beside the house full of steel every 100 yards along the way. I can get real world dope up to the limit of my range and never use a calculator or a chrono. I made the thread as I was curious if anyone else has the seen the same thing. At least one has but most guys seem to be spot on.
I don’t believe BC could account for this discrepancy. It would have to be way off. This also happens across multiple scopes, rifles, cartridges so I don’t believe it’s a scope issue and I take my time to get a solid zero at exactly 100 yards. Scope over bore is correct although this makes little difference inside 1000 yards it seems. I’ll double check everything on my end again and see if anything changes.
Some other things to keep in mind as well are sunlight vs cloudy, mirage, head/tail winds or causing updrafts. At our 1000 yard fclass matches I’ll generally have to adjust my elevation slightly from one relay to the next. Same gun/ammo/target only thing different is the conditions between relays
There is something going on that isn't velocity. I use 4DOF a lot and will be within a couple tenths.
There are an awful lot of inputs that go into a solver, and almost every one of them needs to be right to get impacts on 2-3 MOA plates at 900 yds. In rough order of importance in my mind, separated by "always the same" and "variable," these inputs are:
Essentially always the same:
1) Sight over bore height
2) BC or custom drag curve
3) Twist rate
Variable:
1) MV
2) Air pressure
3) Vertical shooting angle if more than about 8 degrees or so
4) True zero (centered up on POA and at the correct range)
5) Air temperature
6) Finely tuned BC
7) Humidity (doesn't really matter inside 1k)
And I haven't checked all of these side by side, so if someone bothers to run all these down in their solver and re-sort them then power to them. My main point is, all of these things need to be right. The items that are most frequently incorrect in my opinion are sight height and actually zeroed on the paper, rather than close; third most often incorrect in my opinion is environmentals (pressure and temp), and those do matter at long range, hardly at all at 500 yards and absolutely not as much as 75fps MV.
So if you're having to fudge 75 fps, and you got that result on two chronos, you have an issue in your system. Hard for BC to take you that far off at 500, just what's on the box is close enough, so that's likely not your issue. If it were me, I'd do a tracking test on my scope first, then validate zero.
Essentially always the same:
1) Sight over bore height
2) BC or custom drag curve
3) Twist rate
Variable:
1) MV
2) Air pressure
3) Vertical shooting angle if more than about 8 degrees or so
4) True zero (centered up on POA and at the correct range)
5) Air temperature
6) Finely tuned BC
7) Humidity (doesn't really matter inside 1k)
And I haven't checked all of these side by side, so if someone bothers to run all these down in their solver and re-sort them then power to them. My main point is, all of these things need to be right. The items that are most frequently incorrect in my opinion are sight height and actually zeroed on the paper, rather than close; third most often incorrect in my opinion is environmentals (pressure and temp), and those do matter at long range, hardly at all at 500 yards and absolutely not as much as 75fps MV.
So if you're having to fudge 75 fps, and you got that result on two chronos, you have an issue in your system. Hard for BC to take you that far off at 500, just what's on the box is close enough, so that's likely not your issue. If it were me, I'd do a tracking test on my scope first, then validate zero.
How are you measuring groups and how are you measuring the 100 yards? Also on the chronograph, does your optical specify a distance from muzzle and auto-correct or are you doing that math after the fact?
4DOF has been perfect for me if my inputs are right; had an odd match that one time after I did a JB bore scrub, but I didn't validate MV afterwards so I expect I lost some fps. Just had to fudge a tenth up around 500yds and two tenths after 700, validated at the zeroing range. Match went fine, I do wish I'd had time to check the MV though. Next time I do an abrasive scrub I'll make sure I check it.
Maybe your bullets aren’t going to sleep, causing your BC to suffer? I always make sure my bullets go to sleep…
3.2 Effects of Winds - Sierra Bullets
www.sierrabullets.com
Have you done a tall target tracking test on your scope? I once had a Sightron S3 years ago that I had to enter a correction factor of 5% into my rifle profile in the ballistic app for all the predictions to line up with actual. All the scopes I have now are within +/- 1%.
A tall target test can show if your reticle is canted as well. Get a piece of cardboard about 4ft tall and draw a clean straight vertical line on it. Vertically level your tall target line at 100 yards. Chose an aiming spot near the bottom of the line and fire 2 or 3 rounds with just your 100yd zero. Dial 5 mils up and send a few more rounds while still aiming at the bottom spot. Repeat for 10, 15, 20mils or more if your scope has that much travel. Once you have some impacts on paper, you can measure the distance between each group from the aiming spot to check for correct distances apart. Any errors from what you dialed for each increment can be calculated into a correction factor to input into your ballistic app. Any cant of the reticle will show up as groups printing left or right of your vertical line as you dial up.
I've had a few optical chronos through the years and I have seen about a 15-20 fps drop in the readings between a sunny day and a cloudy day. Cloudy days would read lower for me. Luckily, I have never had any in the 75 fps range.
I was chasing my ass one time with my magnetospeed doing load development on my 6.5. It was on normal sensitivity which gave me good results with my .308 F-class loads. On my 6.5 loads, I was catching hell trying to get single digit SDs. Yet, my tight waterline spread on target at 800 yards was definitely indicative of true single digit SDs. I had a hunch and bumped up the sensitivity on the magnetospeed for the smaller 6.5 bullets. The same loads were then indicating single digit SDs. I never did get an error message on any 6.5 shots when sensitivity was set to normal.
A tall target test can show if your reticle is canted as well. Get a piece of cardboard about 4ft tall and draw a clean straight vertical line on it. Vertically level your tall target line at 100 yards. Chose an aiming spot near the bottom of the line and fire 2 or 3 rounds with just your 100yd zero. Dial 5 mils up and send a few more rounds while still aiming at the bottom spot. Repeat for 10, 15, 20mils or more if your scope has that much travel. Once you have some impacts on paper, you can measure the distance between each group from the aiming spot to check for correct distances apart. Any errors from what you dialed for each increment can be calculated into a correction factor to input into your ballistic app. Any cant of the reticle will show up as groups printing left or right of your vertical line as you dial up.
I've had a few optical chronos through the years and I have seen about a 15-20 fps drop in the readings between a sunny day and a cloudy day. Cloudy days would read lower for me. Luckily, I have never had any in the 75 fps range.
I was chasing my ass one time with my magnetospeed doing load development on my 6.5. It was on normal sensitivity which gave me good results with my .308 F-class loads. On my 6.5 loads, I was catching hell trying to get single digit SDs. Yet, my tight waterline spread on target at 800 yards was definitely indicative of true single digit SDs. I had a hunch and bumped up the sensitivity on the magnetospeed for the smaller 6.5 bullets. The same loads were then indicating single digit SDs. I never did get an error message on any 6.5 shots when sensitivity was set to normal.
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If you were running AB and called them and talked to Doc, I'm fairly certain the first thing he would tell you to check is your scope tracking. A tracking error is the simplest explanation of your results, and they see it all the time. NO brand is immune (although some are common offenders while others are rare, but still occur occasionally). Bottom line - unless you've REALLY checked it, don't assume it is correct. Check it. That is the simplest explanation.
That said, I own a MS3 and a Labradar. I have run them simultaneously and they never disagree more than 4 fps, usually less. Both are extremely reliable, and are far superior to the optical chronos. Nowadays I only run the Labradar, because the MS3 does result in POI shifts (lower impacts). That "could" also explain your problem, but reading your post carefully it seems that you aren't just experiencing this with the MS3 attached. Like many here, I have experienced cases where the Labradar and the Kestrel AB using one of their custom curves matched perfectly all the way out to nearly a mile. No MV calibration or Drop Scale Factor corrections were even necessary. Then, changing lot numbers of of the same factory-loaded ammo not only changed the measured MV (negatively), but also the MV and DSF calibration became necessary because the bullet was still under-performing the calculations based off the new, lower input for the accurately-measured MV. I've not seen anything like a 75 fps correction needed, though. More like 10-20. Something is definitely amiss with a 75 fps correction being required, and it doesn't sound like a chrono issue.
That said, I own a MS3 and a Labradar. I have run them simultaneously and they never disagree more than 4 fps, usually less. Both are extremely reliable, and are far superior to the optical chronos. Nowadays I only run the Labradar, because the MS3 does result in POI shifts (lower impacts). That "could" also explain your problem, but reading your post carefully it seems that you aren't just experiencing this with the MS3 attached. Like many here, I have experienced cases where the Labradar and the Kestrel AB using one of their custom curves matched perfectly all the way out to nearly a mile. No MV calibration or Drop Scale Factor corrections were even necessary. Then, changing lot numbers of of the same factory-loaded ammo not only changed the measured MV (negatively), but also the MV and DSF calibration became necessary because the bullet was still under-performing the calculations based off the new, lower input for the accurately-measured MV. I've not seen anything like a 75 fps correction needed, though. More like 10-20. Something is definitely amiss with a 75 fps correction being required, and it doesn't sound like a chrono issue.
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