Let's argue about BC's

[rscott5028]

Naturally, you'll want to avoid circular reasoning. Including all relevant details in your calculations will help avoid that problem. Which is typically what happens in the case of mis-stated BCs.

You seem pretty detail oriented. But, I could see how a shortcut here or there could make a huge difference. ...like all the guys that thought they'd discovered perpetual motion

If it really works, then it seems someone will be putting together a commercial solution if for no other reason than to have an independent method to help validate velocity and BC.

 

[ericpetritz]

Michael,
When you calibrated your scope, how much elevation was dialed in? Did you dial in 35 or 40 MOA of elevation between groups to allow any errors to be more easily quantified? If I understand your data, your scope tracks exactly? The data you provided suggests that the bullet is flying flatter than it should be. I agree that a 200+fps chrono error spread between more than one chrono seems excessive but a 178 grain Amax with an average BC equaling that of a 190 grain Berger VLD (.290 vs. .291) seems unrealisitc as well, which is why I come back to the sights. I assume there was no incline angle during your tests?

Wildcat Bullets,
Getting back to the original point of your thread--I look forward to reading the results of your field testing.

 

[Michael Eichele]

Naturally, you'll want to avoid circular reasoning. Including all relevant details in your calculations will help avoid that problem. Which is typically what happens in the case of mis-stated BCs.

You seem pretty detail oriented. But, I could see how a shortcut here or there could make a huge difference. ...like all the guys that thought they'd discovered perpetual motion

If it really works, then it seems someone will be putting together a commercial solution if for no other reason than to have an independent method to help validate velocity and BC.

You are 100% correct about me being a very detailed indavidual. That is one of the major things that attracts me to LR shooting. It is all in the details. By nature, I am a perfectionist. Handloading and sighting in as well as hitting very small target at LR allows me to satisfy and balance this curse.

That said, I have taken into account the speed of the electronic signals over any cabling distances. High quality devices such as relays and mics will have time factors as well. It is hard to calculate these exact values but you would hope that one next to another would have the same time activation factors. In other words, you have one mic that closes it's swith in .005 of a second, the other should do the same or close to it. That being the case, in theory, one would cancel the other out. Kind of like the perpetual motion devices you refer to. Typically people use magnets to try and accomplish this. Unfortunately, magnets cancel one another out.

It is actually quite funny that you bring this up. I recently was experimenting with perpetual motion devices. The conclusion is that they dont work regardless of what you might see on the internet. This was done for illustration purposes for a hands on lab I was teaching in electric motor theory classes. As you probably know, electric motors work based on magnetism. We use electricity to create a magnetic field to turn a rotor. The idea behind perpetual motion is to use pure magnets instead of electro magnets to turn a rotor. It does not work because it takes an alternation of the magnetic poles for a rotor to turn. Non-electro magnet magnets do not change polarity. We can however reverse the magnetic poles in an electro magnet. This lack of polarity alternation in fixed magnets prevents a rotor from turning plain and simple.

I have a heavy background in electrical systems be it complete building systems to advanced control systems, electrical and electronic theory. From AC theory to transformer theory to motor theory to electronic theory. The most common form of generating electricity in general relies on one thing. Utilizing magnetic fields. I say in general because we can also use batteries and such but that is another subject. Hence the reason so many try and use magnetism as a way to make a perpetual motion device. I also feel that this background will help me make as accurate a system as possible.

M

 

[Michael Eichele]

See bold below:

Michael,
When you calibrated your scope, how much elevation was dialed in? Did you dial in 35 or 40 MOA of elevation between groups to allow any errors to be more easily quantified?

100 MOA. Firing tests were not conducted. Only strict measurment references on a plumb board at a taped 300' from center of scope. Is this the right method? I have no idea but that is what I used. I use .2645" per click on the Mark4 fixed 10.

If I understand your data, your scope tracks exactly?

No but very close. Could I still have an error here? Yes. What I cant figure out is why the same scope would still show different results for the same bullets at different velocities where the velocities were also changed in the program.

The data you provided suggests that the bullet is flying flatter than it should be. I agree that a 200+fps chrono error spread between more than one chrono seems excessive but a 178 grain Amax with an average BC equaling that of a 190 grain Berger VLD (.290 vs. .291) seems unrealisitc as well,

It seems like it on the surface but when you concider that I was using this bullet in 3 different barrels (2 rifles) at 3 different speeds (2550, 2753, 3242) they all showed different Bc's. They all got higher the faster they were driven. .248, 262 and .290 respectively. The only data I have to compare the 190 is between 2657 and 2669 FPS in two different barrels. The BC was nearly identical between them. I dont have any medium velocity data to compare against high velocity data like I do with the 178. Btw, the same scope was used on both rifles. In any event, it seems like a viable explanation (BC's increasing/Decreasing with major velocity changes). (?)

which is why I come back to the sights. I assume there was no incline angle during your tests?

These tests and practice sessions were conducted on a river bottom. Knik River Alaska. There is obviously a mathematical angle to it but it would be so minor at this location you could rule this out. According to Google Earth we are talking about 4' of elevation over the course of 1000 yards. Unfortunately, I cannot shoot there anymore as it has been banned in that area.

I am not trying to be difficult here. Just trying to get to the REAL root of these changes.


Wildcat Bullets,
Getting back to the original point of your thread--I look forward to reading the results of your field testing.

 

[paphil]

I think we should all shoot on the moon for a while ! No air, velocity would remain constant and bullet shape or weight wouldn't matter. There would be no spin drift and with only 1/5 the gravity, we could do some serious long range shooting. Wonder what escape velocity is on the moon? BC wouldn't matter at all. Corioles would be the only thing to mess with. Usually when I have a seemingly unsolvable problem ,I will work on something else that doesn't require much thinking and out of the blue, the subconcious mind will come up with the answer.

 

[groper]

Michael,

Are you forgetting what i mentioned earlier in the thread, regarding super fast magnums and higher G1 BC`s? You really need the G7 number.

Bryan Litz would have probably averaged that 0.74 G1 number over 1000yds, or maybe he has quoted this number at his muzzle velocity, thats the problem with G1 BC, we really dont know!

Regardless, he most likely derived that BC from a much slower caliber than your 3200+fps beast... and as i said earlier, your big magnum will display higher averaged G1`s than slower calibers...

But what are you still doing using velocity dependent, poor model fit G1 numbers, for a VLD bullet in a super magnum anyway?!?!?!

 

[ericpetritz]

Michael,

Are you forgetting what i mentioned earlier in the thread, regarding super fast magnums and higher G1 BC`s? You really need the G7 number.

Bryan Litz would have probably averaged that 0.74 G1 number over 1000yds, or maybe he has quoted this number at his muzzle velocity, thats the problem with G1 BC, we really dont know!

Regardless, he most likely derived that BC from a much slower caliber than your 3200+fps beast... and as i said earlier, your big magnum will display higher averaged G1`s than slower calibers...

But what are you still doing using velocity dependent, poor model fit G1 numbers, for a VLD bullet in a super magnum anyway?!?!?!

He is using a G7 BC of 0.290--there in lies the mystery. Re-read his posts.....

 

[paphil]

Michael, I just remembered a set up on a gun that had the same symptoms that you described. I was using G1 on a customers gun that he assured me was dead on at 200 yards. We shot the data at 500 and1000 and got a real good group at both ranges. Trying to make a drop chart was a dismal failure. On a 7mm with 168 bergers, I was up to 3400fps and BC was below .500. I took the gun back to the range and reshot including 200 yards and the data worked out perfect using the stated BC of.617 and MV of 3025. That short target is critical to the program doing its job and now I shoot it to start and to finish my data. Also don't shoot in wind because for each 3.25 minutes of wind, it will raise or lower your group 1 minute. Left to right = group down, right to left = group up. Good luck!!

 

[Michael Eichele]

Michael,

Are you forgetting what i mentioned earlier in the thread, regarding super fast magnums and higher G1 BC`s? You really need the G7 number.

Bryan Litz would have probably averaged that 0.74 G1 number over 1000yds, or maybe he has quoted this number at his muzzle velocity, thats the problem with G1 BC, we really dont know!

Regardless, he most likely derived that BC from a much slower caliber than your 3200+fps beast... and as i said earlier, your big magnum will display higher averaged G1`s than slower calibers...

But what are you still doing using velocity dependent, poor model fit G1 numbers, for a VLD bullet in a super magnum anyway?!?!?!

Maybe this is why you missunderstand me so much. Go read through my posts. Post 102 in particular.

 

[Michael Eichele]

Deleted for being a smart ***.

 

[eddybo]

Deleted for being a smart ***.

LOL sometimes the internet can be frustrating.

 

[Topshot]

See bold below:

Michael,

How did you calibrate you turret?

100 MOA at 300 feet is 104.7 inches between two marks on a board.

If your scope is an accurate 1/4" per click at 100 yards then it should have taken 418.8 clicks to traverse the 100 MOA (104.7") at 100 yards.

400 clicks would give you 0.26175" per click to traverse this distance between marks. ie 0.25 MOA per click.

Now the figrue of 0.2645" that you quote is interesting. So what are we talking about here inches per 100yards or MOA?

 

[Scot E]

Great discussion guys. I am getting to this thread late but thought I would post some thoughts as well.

It really is of little surprise to me that we have as much variation as we do. In fact at times I am more amazed how accurate we can actually be when using the data we have to rely on. I think of it in this way.

· I use software that hopefully has been programmed correctly but likely has flaws or at least differences among different software manfs.
· I use velocity numbers from a chrony that is not infallible and varies depending on how sunny or cloudy it is. Even the real expensive chronys vary regarding this. Let alone potential errors I may make in setup.
· We calculate scope height but there is varied opinion on how this should be done and it is time consuming project to get all the kinks worked out of scope setup.
· We estimate environmental conditions, hopefully with a calibrated unit, and hope the results we get are accurate. Then there is the argument about how environmental info should be inputted into the program, i.e. station pressure vs elevation, etc. .
· We use BC numbers that are at times incorrect and even the ones I trust are still determined by using chrony's and other equipment that may have calibration issues, and at the end of the day they are averages of a certain number of firings from a specific gun/barrel combo. How does that pertain to our gun/barrel?
· We have turret error, power magnification error, and reticle cant. More specifically sometimes really good scopes will have x click value for a portion of its distance then change as one nears the end of travel. It may be we need stepped click values for inputs just like we have stepped BC inputs.
· We have potential scope to bore alignment issues.
· We shoot in the wind which often plays absolute havoc with much more than our windage numbers. I agree with LTLR that the effects of wind are largely misunderstood and mis calculated for by the shooter and likely the software programs don't adjust for them correctly as well. The speedy Gonzalez wind chart is verified correct among most BR shooters and shows the effects of wind on elevation POI when shooting on flat ground but doesn't correlate to shooting in varied terrain conditions. Like someone else mentioned earlier, shoot near large stands of trees and see how your elevation impact changes. How does a software program properly factor all of this into our outputs?
· We likely have scope zero issues if measurements aren't taken exactly. Most guys use laser rangefinders and they are never exactly dead on accurate. It has been my findings that initial zero errors screws everything up.
· Then we have multiple options in our software programs that can be changed to tweak our numbers. Many times one can change BC, velocity, scope height, and sight in distance to achieve the proper drop change needed at distance to make output match our true drops. But which factor really should have been changed?
· And on and on and on!

I will say that I have had much better success when I follow these measures.

1. Properly setup a scope, checking for all possible issues in mounting, scope/bore alignment, turret error, magnification error, etc. Most guys don't understand all that is entailed in this let alone get it right at setup.
2. When I validate my trajectory I shoot only in no wind conditions. So early and late in the day is about the only time I can do this where I live. I just can't get things to match up if I allow wind to factor in. I also try to find fairly flat land to shoot over as well.
3. I use the advertised BC, especially the G7 from BL or stepped BC G1 numbers, and don't tweak them to start. Instead if I need to change anything I look at velocity, scope height, and zero distance. Adjusting these numbers seems to get me where I need to be most of the time. If I am still off I adjust BC but by doing the above first my BC adjustments are typically minimal.

 

[Michael Eichele]

Michael,

How did you calibrate you turret?

100 MOA at 300 feet is 104.7 inches between two marks on a board.

If your scope is an accurate 1/4" per click at 100 yards then it should have taken 418.8 clicks to traverse the 100 MOA (104.7") at 100 yards.

400 clicks would give you 0.26175" per click to traverse this distance between marks. ie 0.25 MOA per click.

Now the figrue of 0.2645" that you quote is interesting. So what are we talking about here inches per 100yards or MOA?

After digging up my old notes, I see that I did not dial 100 MOA worth of clicks. For whatever reason, that came to mind. Maybe because I was doing this at 100 yards. My appology.

No I did not confuse MOAs with inches. I use an inch per click value when using inches of drop. Hence the .2645" click value (per 100 yards) that I use. When using bullet drops calibrated in MOA I use .250 MOA per click where my software has a 'correction' field to automatically adjust for it to give me real MOA adjustment values. That way if my chart says 28.5 MOA, I know that it has taken the inches of drop and converted it to MOA the way that my scope will track. This is the benefit to writing my own software. I can make it do whatever I want when ever I want to. See screen shot example below:

In any event, this is what I did:

1st, a 10' backer was placed 100 yards.

2nd, I set my scope to 1/2 way between being bottomed out and topped out.

3rd, the scope was attached to a benchrest with rings, shims and a rail screwed to the bench for a solid support. As level as possible. It was done so that the crosshair was close to the middle of the backer.

4th, a friend of mine held a marker out on the backer and moved it slightly until I was happy with how it was lined up with the crosshair where he made a mark.

5th, the turret was moved up 100 clicks. He remarked the backer at the crosshair junction. The turret was moved down 200 clicks. Another mark was made there.

6th, these marks were measured (using inches of course) and the math was applied.

In short, it worked out to .2645" per click or .2526 MOA per click. The 10' backer was a waste of time. It could have easily been done with a much shorter backer. This is how we learn.

IMHO, it is a waste of time. The difference works out to about 2.5" at 1K when dialing 300" worth of drop. It would only take a small fraction of BC to make up for it. For all I know, the differences stem from inaccuracies on my part which may explain why there was a difference of 0.05" between the upper adjustment and the lower. That said, since it was such a pain in the ***, I have never done this test to my Nightforce. That is why any of my previous posts in this thread are based off of my Lupy and not my NF.

A little bit about the formulas I use in my software. Depending on options that are selected, you can get an accurate adjustment value for clicks, MOA, Mils etc.......

When selecting clicks, the code reads like this:

(DRP40 / ((((CrtMOA – MOAclk) + MOAclk) * 1.047) * YDG40 / 100))

When selecting MOA, the code reads like this:

(DRP40 / ((((CrtMOA – MOAclk) + MOAclk) * 1.047) * YDG40 / 100)) / (1 / MOAclk)

'DRP40' is the drop inches in the 40th box. CrtMOA is the calibrated MOA per click value, MOAclk is the stated click value in MOA, YDG40 is the yardage text that corosponds to the 40th drop value. The default for the MOA corrections option is the same as what is entered into the standard box but can be changed to my liking.