For years, I've been wanting a very accurate ballistic calc and really haven't been happy with any of the ones I've used. Shooter, on my iphone has been pretty close for me. always within .2 mil but that's often not good enough when you're shooting sub MOA targets. I also have KAC's BulletFlight and use JBM and several others, which all seem to be in the same boat. Usually, I think the problem is GIGO, but it's just always bothered me that the math should be closer, given the accuracy of the inputs.
So this Spring, I picked up a copy of Field Firing Solutions Delta V in the snipershide group buy from Ashbury which bundled the software with a vectronix PLRF10C. Over the summer, I bought a used Nomad (pic from FFS website) to run it on and I played with it a bit but was extremely disappointed that i couldn't get good data out of it.
Using the exact same inputs I use on another calc, I would get answers that were several tenths off. Frustrated by the time consuming suggestions to resolve the problem, I put it away for a few months. But this week, I decided to spend the time to really try it, and so I called the guy who wrote the software for some technical support and he was extremely gracious and spent a great deal of time correcting a lot of my misconceptions; about different drag functions used by different calculators, G1 vs G7, and especially the need to calibrate everything with real data. He patiently repeated the suggestions from his instruction videos: that I spend the time to calibrate both the muzzle velocity and the BC.
This post is about my experience with that process, which was a lot more effort than I wanted to go through, but was ultimately pretty successful.
To summarize, the challenge is there are 2 unknowns in the equation: muzzle velocity and ballistic coefficient. We have a chronograph to measure one, but it is likely not calibrated properly and thus not really trustworthy. We have published BCs for the other which are often pretty sketchy but even the good ones don't account for variations in bullet lot.
So how do you solve the problem? Blane's solution is based on the fact that at shorter distances, environmentals and BC don't make much difference, so you should shoot at something around 400 yards away and measure your drop and calculate your muzzle velocity based on this. Then, shoot at something at the farthest possible distance before your bullet gets into the transonic range. Using your recently calculated MV, you can now calculate the drop due to drag on the bullet. Once both are known, your calculator should be spot on within a velocity range.
SO... I start the process with one shot on a 5/8" dot to confirm zero, then I move back to 354 yards and shoot 3 rounds on paper. It was pretty stormy with winds gusting pretty bad and I couldn't see my impacts on paper, so I just guessed at my wind. The two shots on the left were a favor right and the other was a right edge hold.
Anyway, the zero looks good enough (not going to quibble over 1/4" low) and I'm going to say the average of the other 3 are about 1" low.
The velocities as measured by the magnetospeed are in the first column in the spreadsheet at the bottom of this post. They average 2941 fps, though when I use the FFS to calculate my mv based on drop, it tells me 2922 fps.
(note: if you're wondering where the 5th shot went, in the middle of my string, i decided to put round number 4 on the ipsc target head. no idea why. I just did. it's the one in the center.)
I went ahead and finished the process by shooting at distance (see other hit on the ipsc head link above from 1008y), but the numbers didn't work out. I get a BC of .6614 which works at some distances but not at others. So, the next day, I call back am advised that 350 is a little short and i should to try do 450 yards. (I secretly suspect it was the 10-20mph winds and not the distance that put me off, so...) I go out again today with light variable winds to shoot a more optimal distance. Unfortunately, being an idiot, I left my paper target at home and had to set up today on a 436 yard steel plate. Holding in the center of a 10" plate is kind of a guessing game, but I shoot 3 rounds on this target, with a bad trigger pull on the 3rd shot, so I ignore that from the group. (and then 2 at this 4" circle for no good reason).
Pretty sloppy shooting on the big plate and I am holding my thumb over 1/2" or so of the tape measure, but ignoring the shot i pulled, I figure I need to come up .5 inches. Using the FFS MV calculator, I get 2956 fps. Not too far off of what the magnetospeed says, but quite a ways away from the 2922 previously calculated. (an interesting side note: if i kept the 3rd shot and my group averaged POI=POA, I would still make a mv adjustment based on zero impact shift, because.... the calculator says my solution is 1.831 mils so the fact that my bullet says 1.800 means i'm off 0.031 mils. I know, I know. In that event, FFS computes my MV at 2936. Granted, all of this is based on pretty small sample size.)
Anyways, now that I have good guess at my actual muzzle velocity, it's time to see what the bullet thinks its BC is for the FFS drag function. So I back up to my 1008 yard target and take a couple pokes at the head on this full size ipsc. (first round fired on the body just to make sure my wind call was good, then rounds 2 and 3 at the head.) If I figure the center of the group is at the 2" mark, and the POA was at the 5.5" mark, that's 3.5" low.
(so again, being an idiot, I actually got the 7.3 mil solution from my iphone instead of FFS, and when I got home I realized FFS needs me to measure the difference between POA and POI using it's 7.1 mil solution, which was based on a bogus BC i'd calculated previously using bad velocity. If I'd held that, I would have been .2 lower. so quickly, at 1008y, the .2 mil difference is 7.26", plus my 3.5" low figure, gives me a net of 10.56" low.)
So, I input the data into FFS and it gives me a warning that my velocity at that distance is 1673 fps, above the optimum range of 1250-1500 fps, and suggests I shoot at a longer distance, but asks if I want to continue. well of course I do... so it thinks for a moment and outputs the answer: .6178 (Litz wrote .618 on the box the Bergers come in, but what does he know, right?
)
So I select "use BC in firing solution" and it updates it to 7.39 mils up, which looks perfect to me.
But I go ahead and put my last 2 rounds of the 5 rounds on my 12" plate at 1087 yards. My Iphone tells me 8.3 mils. With a right favor, I BARELY catch the edge of the target with the first round, so I hold right edge on the second and center it up a bit. Looks like about an inch of vertical, centered on 1.75" mark. With POA at 6", that is 4.25" low.
Now, with my good BC, FFS tells me the solution is 8.43 and to dial 8.4 on the turret. At that distance, the .1 mil is worth 3.9" up, so I'm going to subtract that from the 4.25" low and say my shots were .34" low. Going into the BC calculator tool, I again get a warning that my 1504 fps MV is out of the 1250-1500 fps optimum range. Undaunted, I press on. FFS doesn't mention anything about how silly trying to correct 1/3" is at almost 1100 yards. It gives me a .6172 answer. I think I'll stick with .618.
Below are the magnetospeed readings for the 3 groups shot on 2 different days at 3 different temperatures. I used my previously calculated FPS/*F factor to adjust the 64* and 62* down to 60* numbers and averaged them all together. Not my best ES for sure, but not completely embarrassing.
If accurate, the average would mean my magnetospeed is about 14 fps slow, which is half a percent (0.47%) off. Not bad.
What is somewhat frustrating and remains a mystery is that I started in almost the same place I ended, using Litz' .618 bc and a 2950ish velocity as my inputs but now my data matches where previously I was getting numbers about .3 mils off.
In any event, i appreciate the education and learned a lot from the experience. I think the process works, and should work regardless of which calculator you use, although FFS certainly makes the math easier with a built in tool to correct your MV and BC based on measuring your impacts.
I'm looking forward to trying this with a larger sample size when the weather improves, but I don't expect the answer to change.
FFS also includes tools to correct for small deviations in your scope turrets, but fortunately I haven't needed to do that.
The targets above were shot with a slow practice load in 260AI (the rifle in the back) and with the magnetospeed bayonet attached (obviously).
So this Spring, I picked up a copy of Field Firing Solutions Delta V in the snipershide group buy from Ashbury which bundled the software with a vectronix PLRF10C. Over the summer, I bought a used Nomad (pic from FFS website) to run it on and I played with it a bit but was extremely disappointed that i couldn't get good data out of it.
Using the exact same inputs I use on another calc, I would get answers that were several tenths off. Frustrated by the time consuming suggestions to resolve the problem, I put it away for a few months. But this week, I decided to spend the time to really try it, and so I called the guy who wrote the software for some technical support and he was extremely gracious and spent a great deal of time correcting a lot of my misconceptions; about different drag functions used by different calculators, G1 vs G7, and especially the need to calibrate everything with real data. He patiently repeated the suggestions from his instruction videos: that I spend the time to calibrate both the muzzle velocity and the BC. This post is about my experience with that process, which was a lot more effort than I wanted to go through, but was ultimately pretty successful.
To summarize, the challenge is there are 2 unknowns in the equation: muzzle velocity and ballistic coefficient. We have a chronograph to measure one, but it is likely not calibrated properly and thus not really trustworthy. We have published BCs for the other which are often pretty sketchy but even the good ones don't account for variations in bullet lot.
So how do you solve the problem? Blane's solution is based on the fact that at shorter distances, environmentals and BC don't make much difference, so you should shoot at something around 400 yards away and measure your drop and calculate your muzzle velocity based on this. Then, shoot at something at the farthest possible distance before your bullet gets into the transonic range. Using your recently calculated MV, you can now calculate the drop due to drag on the bullet. Once both are known, your calculator should be spot on within a velocity range.
SO... I start the process with one shot on a 5/8" dot to confirm zero, then I move back to 354 yards and shoot 3 rounds on paper. It was pretty stormy with winds gusting pretty bad and I couldn't see my impacts on paper, so I just guessed at my wind. The two shots on the left were a favor right and the other was a right edge hold.
Anyway, the zero looks good enough (not going to quibble over 1/4" low) and I'm going to say the average of the other 3 are about 1" low.
The velocities as measured by the magnetospeed are in the first column in the spreadsheet at the bottom of this post. They average 2941 fps, though when I use the FFS to calculate my mv based on drop, it tells me 2922 fps.
(note: if you're wondering where the 5th shot went, in the middle of my string, i decided to put round number 4 on the ipsc target head. no idea why. I just did. it's the one in the center.)
I went ahead and finished the process by shooting at distance (see other hit on the ipsc head link above from 1008y), but the numbers didn't work out. I get a BC of .6614 which works at some distances but not at others. So, the next day, I call back am advised that 350 is a little short and i should to try do 450 yards. (I secretly suspect it was the 10-20mph winds and not the distance that put me off, so...) I go out again today with light variable winds to shoot a more optimal distance. Unfortunately, being an idiot, I left my paper target at home and had to set up today on a 436 yard steel plate. Holding in the center of a 10" plate is kind of a guessing game, but I shoot 3 rounds on this target, with a bad trigger pull on the 3rd shot, so I ignore that from the group. (and then 2 at this 4" circle for no good reason).
Pretty sloppy shooting on the big plate and I am holding my thumb over 1/2" or so of the tape measure, but ignoring the shot i pulled, I figure I need to come up .5 inches. Using the FFS MV calculator, I get 2956 fps. Not too far off of what the magnetospeed says, but quite a ways away from the 2922 previously calculated. (an interesting side note: if i kept the 3rd shot and my group averaged POI=POA, I would still make a mv adjustment based on zero impact shift, because.... the calculator says my solution is 1.831 mils so the fact that my bullet says 1.800 means i'm off 0.031 mils. I know, I know. In that event, FFS computes my MV at 2936. Granted, all of this is based on pretty small sample size.)
Anyways, now that I have good guess at my actual muzzle velocity, it's time to see what the bullet thinks its BC is for the FFS drag function. So I back up to my 1008 yard target and take a couple pokes at the head on this full size ipsc. (first round fired on the body just to make sure my wind call was good, then rounds 2 and 3 at the head.) If I figure the center of the group is at the 2" mark, and the POA was at the 5.5" mark, that's 3.5" low.
(so again, being an idiot, I actually got the 7.3 mil solution from my iphone instead of FFS, and when I got home I realized FFS needs me to measure the difference between POA and POI using it's 7.1 mil solution, which was based on a bogus BC i'd calculated previously using bad velocity. If I'd held that, I would have been .2 lower. so quickly, at 1008y, the .2 mil difference is 7.26", plus my 3.5" low figure, gives me a net of 10.56" low.)
So, I input the data into FFS and it gives me a warning that my velocity at that distance is 1673 fps, above the optimum range of 1250-1500 fps, and suggests I shoot at a longer distance, but asks if I want to continue. well of course I do... so it thinks for a moment and outputs the answer: .6178 (Litz wrote .618 on the box the Bergers come in, but what does he know, right?
)So I select "use BC in firing solution" and it updates it to 7.39 mils up, which looks perfect to me.
But I go ahead and put my last 2 rounds of the 5 rounds on my 12" plate at 1087 yards. My Iphone tells me 8.3 mils. With a right favor, I BARELY catch the edge of the target with the first round, so I hold right edge on the second and center it up a bit. Looks like about an inch of vertical, centered on 1.75" mark. With POA at 6", that is 4.25" low.
Now, with my good BC, FFS tells me the solution is 8.43 and to dial 8.4 on the turret. At that distance, the .1 mil is worth 3.9" up, so I'm going to subtract that from the 4.25" low and say my shots were .34" low. Going into the BC calculator tool, I again get a warning that my 1504 fps MV is out of the 1250-1500 fps optimum range. Undaunted, I press on. FFS doesn't mention anything about how silly trying to correct 1/3" is at almost 1100 yards. It gives me a .6172 answer. I think I'll stick with .618.
Below are the magnetospeed readings for the 3 groups shot on 2 different days at 3 different temperatures. I used my previously calculated FPS/*F factor to adjust the 64* and 62* down to 60* numbers and averaged them all together. Not my best ES for sure, but not completely embarrassing.
If accurate, the average would mean my magnetospeed is about 14 fps slow, which is half a percent (0.47%) off. Not bad.
What is somewhat frustrating and remains a mystery is that I started in almost the same place I ended, using Litz' .618 bc and a 2950ish velocity as my inputs but now my data matches where previously I was getting numbers about .3 mils off.
In any event, i appreciate the education and learned a lot from the experience. I think the process works, and should work regardless of which calculator you use, although FFS certainly makes the math easier with a built in tool to correct your MV and BC based on measuring your impacts.
I'm looking forward to trying this with a larger sample size when the weather improves, but I don't expect the answer to change.
FFS also includes tools to correct for small deviations in your scope turrets, but fortunately I haven't needed to do that.
The targets above were shot with a slow practice load in 260AI (the rifle in the back) and with the magnetospeed bayonet attached (obviously).
