I told you something was weird. The vel was off a new Chrony at around 10ft. Did a few shots to get the vel. average. Have used this chrony to compare with other of my rifles and it matches. At worse, it is reading FASTER which would make the BC even higher!!!
To match my data, I am getting BC at 1 and higher. Bizarre.
Took it out yesterday morning and the come ups were again verfied. Then I started using the mil-dots at the preset mag (have confirmed mil dots subtend correctly at 100yds). Sure enough, bullets hit where they were supposed to.
So even if the turrents moved more then the clicks indicate, the mil dots are using the same amount of MOA elevation for the distance as the turrents.
Most of the shooting has been level to only a few degrees up. Weather has been warm to hot, dead calm and clear. Low humidity - perfect shooting weather.
I have always known that the Hornady poly tipped bullets had higher real world BC's then what was printed. I also expected these 140gr SST to be much higher then the 142gr MK and Lapuas because the SST are much longer.
Never thought it would be that high.
I know the bullet is not going faster then 2975fps because I am only using an '06 case and 58.5gr of H4831SC. A 6.5Win Mag load uses a lot more powder to go over 3000fps. Barrel length is 24" so we are in standard/well known territory.
Using Weaver bases and High Burris rings. haven't measured the scope height but not overly high.
All you 6.5 shooters may want to give this bullet a look. It will stabilize in 9 twist barrels and it does shoot very well. Would love to hear if anyone gets similar results.
Your results are very screwy and don't make much sense. But I learned long ago, never say never, cause screwy stuff is what this world go round.
However, I would never trust a chrony. I have two as well as two Millenium CED chronographs. My chrony's have been back twice to be checked and recalibrated and they are so inconsistent it is not funny. But the two CED's are within a foot per second of each other when placed right behind each other. My two Chrony's can be 200 fps faster or slower than the CED's.
If you want to figure out what you actual BC is. Move the chrony out to exactly 100 yards. Not close to a 100 or a laser ranged 100 yards, but exactly 100 yards and get an average velocity reading. Post your results and I'll let you know your actual BC is.
Hope it helps,
Distance is not an issue, but the wind will make it interesting!
Any chance of you posting this information over on either www.long-range.com or the 1k BR forum at www.benchrest.com? Some ballistic weenies hang around there and might be able to forward an idea as to what is going on. Try as I may, I can't bring myself to believe that a Hornady 140gr SST has a B.C. that much higher (0.2+!!) than any of the target VLD's on the market that aren't made out of some exotic material.
That's just it... it *doesn't* work out, because a G7 B.C. of ~0.5 translates to about a 0.8 or 0.9 G1 B.C. which seems entirely unrealistic. Yes a G5 or G7 B.C. is technically more accurate, but we are talking small amounts here. Figuring the drop for a 142gr SMK out of my 6.5-08 w/ a G1 B.C. of .595 as compared to a temperature/altitude/humidity corrected G5 B.C. of something like .409 (don't have it right in front of me so I may be off there) results in something like less than 1/2 MOA difference @ 600yds.
Another thing to maybe check would be to try a different box of the same lot of bullets, and a different box of a different lot of the SSTs. If the results are consistent, and we can't come up w/ some other explanation... man I hope Hornady is stocked up on these puppies, cuz once the LR competition shooters find out about this... [img]images/icons/grin.gif[/img]
Ok, this is fun. I'm an aerospace engineer. I love ballistics. I can't explain everything, but I enjoy the study. First, a published BC should have been determined by testing over a variety of distances. What happens when we plug what we think we know into an equation, and the results don't match our prediction? We have long discussions about it on forums. Most of these posts focus on trying to prove that the measurement must be off rather than discussing whether or not the equation was correct. Some constant, variable, or group of variables must be incorrect if the results don't match the prediction.
What makes one drag function more correct than another? If a certain standard drag equation defines a particular bullet shape, what happens if you build a different shape bullet? The answer is that the equation that defines the performance of one bullet doesn't fit all other bullets. BC is part of the equation. - just one variable. Change a constant, like the shape of the bullet, and the relationship of all the variables changes also.
When a BC is published, do the manufacturers give you all the math behind their claims? What drag function best describes their bullet at a given velocity? Never have seen that on a box of bullets.
The best way to predict bullet drop is to do exactly what Jerry is doing - measure the results and then try to find an equation that defines them. No single formula can fit all the variables. In this case, the G7 drag function more closely matches the measured results than the G1.