Georgek80 Posted July 5, 2014 Report Share Posted July 5, 2014 Can anyone help When ever I have cronographed any of my rifles then set all the details into my ballistic calculator I then try my rifle at 300 yards the shots are always about 2 inch high so i have to put in a faster velocity in the ballistic calculator untill the extra height is compensated with less moa I then try rifle at longer ranges and the moa I put in with the untrue velocity is spot on I the have tried using different ballistic calculators and this always happens I am putting all the correct bc and velocity scope height ect in and I the cronograph seems fine I always put a few shots through it with .22 rifle and speed is same on box I'm am using two nightforce scopes and a ior scope which have never let me down Link to comment Share on other sites More sharing options...
simonl Posted July 5, 2014 Report Share Posted July 5, 2014 Is your zero distance accurate? Link to comment Share on other sites More sharing options...
Georgek80 Posted July 5, 2014 Author Report Share Posted July 5, 2014 Yes zeroed bang on at 100 yds use lica rangefinder to confirm distance thanks Link to comment Share on other sites More sharing options...
gbal Posted July 5, 2014 Report Share Posted July 5, 2014 Hmmm....the data from 100y has to be very accurate-ie -not 1/4 inch out- have you tried using actual fall of shot data from 300y..(and of course appropriate BC (apart from G1 and G7 versions-whichever your program uses) the published BCs are 'best' ones-BC varies across velocity/range -and manufacturersseldom tell you just how they measured their quoted value.....you are shooting over pretty level ground,presumably? The proof is always on the target,and all programs have 'assumption' rather than holy grail provenance. Yours is not an unusual scenario....and not everyone checks out the program 'predictions' against actual reality...good you checked your chrono too-some (makes) do give consistent lo/hi readings...magneto seems pretty accurate... if it can be measured,measure it...but if it can be measured,it can be measured incorrectly! At least you know what your pet is doing. Link to comment Share on other sites More sharing options...
Georgek80 Posted July 5, 2014 Author Report Share Posted July 5, 2014 I'm am using a chrony cronograph and my bc is 0.238 Nosler 50gr bullet head loaded with varget three shot av 3456 fps caliber 22-250 flat 100yd range three shot group size is under 1/4 inch I also have same problem with my .260 but I don't have to worrie about that for a few weeks as its getting rebarreled Link to comment Share on other sites More sharing options...
DW58 Posted July 5, 2014 Report Share Posted July 5, 2014 Perhaps check your Chrony against another chronograph - clearly something is not quite right and verifying the accuracy of your MV readings is one way or eliminating any variables. Speaking of Chrony chronographs - I witnessed this last week, not mine I might add, but the Steinert SuperChrono is. Oops! 155gr SMK 1 : Chrony 0 Apologies for the crappy phone pix. Link to comment Share on other sites More sharing options...
Georgek80 Posted July 5, 2014 Author Report Share Posted July 5, 2014 I will do that next chance I get thanks Link to comment Share on other sites More sharing options...
onehole Posted July 12, 2014 Report Share Posted July 12, 2014 Hi,,,long time ago now but in my air rifle field target days many people used to bring their chronys with them just to check their rifle in case of being caught being over the limit.On one occassion we lined up about six chronys just to check if there were any differences and there clearly were with + or - 20 fps variance!! I pretty much suspect my own chrony to read a bit fast and have to fudge ballistics a little to compensate. With an accurate 200 zero I can reliably dial to a 500 yard tennis ball on good days .... As Gbal suggests and I agree that a 100 yard zero has to be so very very accurate,,,,,in fact I will stick my neck out and say 100 yard zero,s are a waste of time unless you just get lucky,,,,,yep go further out.Best of luck,,,,O Link to comment Share on other sites More sharing options...
gbal Posted July 12, 2014 Report Share Posted July 12, 2014 20 fps sounds quite good,really-and if repeated for cf would not contribute much error...but the point about a longer zero holds......I keep advocating a zero at the modal shooting range for field use-of course for target use this is done anyhow-1000 yard shooters zero at 1000y! It would not be a bad idea to have real data anchor points at say,100,200,400 if possible-in the final analysis,holes on paper are the truth.Careful measurement of a decent sample is needed,and under the elusive "good/ideal conditions"-but see following: BD has also 'suggested' atmospheric effects on POI-in another thread-maybe .5moa-if this checks out,then dull/bright shooting differences between zero and longer targets might explain some of the discrepancies reported.New to me,with optical sights,but def interesting,and unlikely to be in every ballistic program? I suspect very,very few such programs are comprehensive-but most do give a pretty good representation,and of course can be tweaked to fit the input data,so you are at least in the small ball park. Link to comment Share on other sites More sharing options...
247sniper Posted July 12, 2014 Report Share Posted July 12, 2014 I have had the same experience, with all my rifles, I thought they all can't be doing the same thing. All the ballistic data was alway suggesting more elevation needed then in the field actually required. I have since traced it back to my chrono being faulty, it seems it is very accurately reading 5% lower then what the bullets are actually doing. + 5 % on the chrono reading and all my rifles are now bang on. I too had to fudge the fingers before hand to make everything all work. Time for a new chrono me thinks. Steve Link to comment Share on other sites More sharing options...
onehole Posted July 12, 2014 Report Share Posted July 12, 2014 20 fps sounds quite good,really- Think what I ment was accepting that one chrono was correct others gave up to 20fps more or less velocity ,,,so a 40 fps across all the chronos,,,,this is at .177 speeds not sure if the error would magnify at cf speeds ?? anyone??,,,,,,,,,,,regds ,,Onehole Link to comment Share on other sites More sharing options...
brown dog Posted July 12, 2014 Report Share Posted July 12, 2014 so i have to put in a faster velocity in the ballistic calculator untill the extra height is compensated with less moa I then try rifle at longer ranges and the moa I put in with the untrue velocity is spot on If that works, then just stick with that - why care how the inputs are 'massaged' if they're giving you perfect firing solutions. Don't lose sight of the fact that you've achieved the desired endstate of ballistic prediction: Perfect firing solutions. If you've got those, then happy days and STOP there don't waste time/effort chasing an irrelevant 'error': The purpose of your shooting is to hit the target; not to calibrate your chrono. Link to comment Share on other sites More sharing options...
gbal Posted July 12, 2014 Report Share Posted July 12, 2014 +1 : if ballistic program predictions and reality (holes on target) match up,Valhala! There are just so many factors -or program variables-known/unknown that might be discrepant,you might never be done empirical testing.No measure-BC,chrono,whatever-is error free and without variation.Now you have it matched,just use it. Link to comment Share on other sites More sharing options...
Georgek80 Posted July 13, 2014 Author Report Share Posted July 13, 2014 Thanks for everyone's imput ,once i get my 260 back will try with that if still the same I will get a new crono my other rifles are bang on at 100 yds and all data right so it's mind boggling to me Link to comment Share on other sites More sharing options...
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