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Range Report JBM dope card is screwing with me. Starting to get frustrated! What am I missing!?!
- Thread starter ScottyD
- Start date
I'd love to check out that video. I dig a little digging and wasn't able to find it. Is it part of your online tutorials? Or should I look for it someplace else?
Thanks for the advice Steve! I appreciate the tips. I used to be real good about not making dumb mistakes -I think FT competition helped with that. I was never the guy who forgot to dial or shot at the wrong target..until just recently. I think now I'm starting over think stages and stress myself out, then I get flustered these days... Bad dope hasn't been helping with that. I need to settle down a bit and come in a bit more confident about my equipment. Seems like I'm still learning and experimenting with different stuff every time I step up to the line. I could see where a consistent routine every time you step up to a stage would be best (but at the same time, a lot of these matches throw weird stuff at you , so you have to be ready to adapt on the fly). I'm still trying to figure out the smoothest most consistent way to get things done once that clock starts... And different match formats send you down different paths with that stuff...I also notice that if I want to be serious about a match, I have to really focus up and stay organized rather than just hanging out and BS'ing with the guys... I've been trying to force myself to slow down a bit and make sure my position is solid. Taking a few extra seconds to find that natural point of aim and stuff has been helping -when I remember to do it! But I hear ya: no need to give points away with dumb mistakes. Step 1: no more wasting ammo with bad dope! (hopefully!)...
Hi 17847. I noticed up to a full mil of difference when switching from G1 to G7 @ 1k when playing with JBM. I'm getting the same numbers you're getting with your shooter ap: and that's the problem -that's not what my gun is doing! Your numbers get me on at 700, but have me missing closer and longer shots. But are you saying g1 works out better for you than G7?
Hey there COFOX! Welcome to the fight against bad dope! I put your numbers into JMB with a velocity of 2850fps, 66F, 4850 for alt, 50% H, and left pressure at 29.92, NO LITTLE BOXES CHECKED and I get a perfect match to what you're seeing, with the exception of 521 (its giving me 2.7 for 525). Try it and take a look at 1000, 800, 600, 440, and 300.. They all match what you're telling us... I hope that helps.
Do you know what your watch baro was telling you that day? Do you still have that number? If so, try putting that in with 2850fps, 66F, zero altitude, and 50% H, NO boxes checked... and let me know what you get...
Cool, thanks! The discrepancy at 521 could be bad range estimation on my part. I'll call it 500 even.
I neglected to use my watch's baro because iSnipe doesn't use inHg, and I didn't realize JBM did until after, or I would have looked at it...d'oh!I just used: 2850 fps, 4,825' ASL, 66 F, 30% hum, 29.77 inHg, no boxes checked, and it all looks real damn close/good.
So my actual muzzle velocity IS 2,850?!?! I really need a reliable chrony!
Cool, thanks! The discrepancy at 521 could be bad range estimation on my part. I'll call it 500 even.
I just used: 2850 fps, 4,825' ASL, 66 F, 30% hum, 29.77 inHg, no boxes checked, and it all looks real damn close/good.
So my actual muzzle velocity IS 2,850?!?! I really need a reliable chrony!
If you are at 4825 ft there is no way that your uncorrected pressure is 29.77.
OK, so 4,825' ASL, pressure set to 25.00 inHg, 50% humidity, 66 F temp, and put a CHECK mark in the "Pressure is corrected" box? From there I should then mess with MV until I get a match? This is starting to make sense.
If I do the above, no matter what MV I enter, I cannot get my drops to match what I had in the field. They're either good out to 440, then fall apart at longer distance, or they're good at distances of 600+, but not closer.
The way I have it above, 29.77 inHg, 2,850 fps, unchecked box, it matches perfectly at all distances. I just need a friggin' chrony.
Yes, a chrony is great, but if you are not correctly inputing the atmospheric data you are still going to be chasing your tail.
My default is to ALWAYS use actual station pressure as measured by my watch barometer; that and the current temp and an estimated mv is all the data that I need to get started. A chrony will get you very very close, but keep in mind that all chronys are not created equal, and can give false data.
This barometric pressure thing seems to be confusing a lot of folks. Shooters should strive to use the station pressure at the firing point as measured by themselves. Keep in mind that sea level is about 30.00 (okay, its 29.92, but I round for simplicity) and every 1000 ft elevation gain equals about 1 inch of Hg (again, not exact, but close). Also, pressure will change with the weather, but rarely more than .5 inch in either direction from average.
My default is to ALWAYS use actual station pressure as measured by my watch barometer; that and the current temp and an estimated mv is all the data that I need to get started. A chrony will get you very very close, but keep in mind that all chronys are not created equal, and can give false data.
This barometric pressure thing seems to be confusing a lot of folks. Shooters should strive to use the station pressure at the firing point as measured by themselves. Keep in mind that sea level is about 30.00 (okay, its 29.92, but I round for simplicity) and every 1000 ft elevation gain equals about 1 inch of Hg (again, not exact, but close). Also, pressure will change with the weather, but rarely more than .5 inch in either direction from average.
You don't want to check the box - 25.00 inHg is absolute (aka station, aka uncorrected) pressure. Corrected pressure is always near 29.92 inHg.
Weather man pressure = checked. Absolute pressure = unchecked. Absolute is better if you have it.
Remember, what's going on here is that the meteorologists take the (always lower) absolute pressure and "correct" it so that they can directly compare pressures everywhere as if they were the same (or something like that, I'm not a weather geek). Nobody else cares about corrected pressure. If you're seeing a number like 23 inHg or even 27-28, it is going to be an absolute pressure every time. If you're seeing something near 29.92, and your'e not at sea level, you're probably looking at a corrected pressure. This is usually a pretty obvious difference unless your'e stuck down at 500 feet, where it can be harder to tell. (I'm at 1000 feet, and the absolute pressure here is ~28.5 inHg). If you're at sea level, you can check the box or not - it's all the same.
This is partly so confusing because of the way JBM labels the box - "Check this box if the pressure entered is a corrected station pressure. If it is an absolute pressure, leave this unchecked."
If you're not totally familiar with the concepts, it's possible to read that statement as contradictory and just get confused - ("Wait - I thought station pressure was uncorrected? WTF?").
I just tried pressure at 25.00 in Hg, H 50%, 67 F, 0 altitude, and I have to drop to 2740fps to get COFOX on 7.8mil @1k.. but all the other distances are off a click or two...
I also tried pressure at 25.00 in Hg, H 50%, 67 F, 4850 altitude, and nothing changed... on at 1k with 7.8mil at 2740fps but everything else off a click or two...
No little boxes checked in both cases...
Not understanding why, just reporting what I'm seeing. Very interesting that 29.92in Hg is working out so well for both of us (I used 29.92 for his and my numbers, he used 29.77)... Damoncali explained why, but I also wonder if its working out so well because we just happen to be so close to that standardized temp of 59 F.... (59 F goes hand-in-hand with 29.92 on that sable chart...)...
Thoughts on this, anyone?
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You can tweak the B.C., you can tweak the MV, you can re-fire and check your data (human error is a variable ever present).
Remember, JBM or Shooter or whatever is just a prediction; what you see is reality. That said, these programs are pretty darn good now, but the inputs have to be spot on correct.
Remember also that we are swaging the station pressure because you did not record it, so we are a bit bassakwards here.
Remember, JBM or Shooter or whatever is just a prediction; what you see is reality. That said, these programs are pretty darn good now, but the inputs have to be spot on correct.
Remember also that we are swaging the station pressure because you did not record it, so we are a bit bassakwards here.
The 29.92 is just being offset by the altitude, 25.00 here for pressure is probably a bit rounded, as it's almost never that exact.
I am uploading a short video now, but it works equally either way, all you need to do is tell the software, Barometric or Absolute / Station Pressure then it gives you the option to include Altitude or not. But all the software is really gonna do is subtract the 1" per 1000ft.
All of these should be within 1 MOA, there are a ton of variables not included in the software, so it's not gonna everything, but it needs to know enough and from there it will give you a good "prediction" on where the bullet should go. If you are within 1 MOA or .25 Mils you are solid, after that you can true and adjust.
Winging it like some of you guys are, you cannot expect it to be any better. You're guessing on MV, you're using advertised BCs, etc. That increases the chance of error with the PREDICTION... You have to do your part, which is gather accurate information, dope the rifle on a verifiable target, and then do your part when shooting it.
Remember in the old days, the manufacturers data tables were designed to get on paper on an NRA Target which is 6'x 6' in size.
I am uploading a short video now, but it works equally either way, all you need to do is tell the software, Barometric or Absolute / Station Pressure then it gives you the option to include Altitude or not. But all the software is really gonna do is subtract the 1" per 1000ft.
All of these should be within 1 MOA, there are a ton of variables not included in the software, so it's not gonna everything, but it needs to know enough and from there it will give you a good "prediction" on where the bullet should go. If you are within 1 MOA or .25 Mils you are solid, after that you can true and adjust.
Winging it like some of you guys are, you cannot expect it to be any better. You're guessing on MV, you're using advertised BCs, etc. That increases the chance of error with the PREDICTION... You have to do your part, which is gather accurate information, dope the rifle on a verifiable target, and then do your part when shooting it.
Remember in the old days, the manufacturers data tables were designed to get on paper on an NRA Target which is 6'x 6' in size.
The "pressure is corrected" box doesn't mess with temperature. All it does is translate between corrected pressure and absolute pressure. Since you didn't have the box checked, entering the altitude doesn't do anything at all- the program ignores it. It only needs altitude if the box is checked because it needs it to un-correct the pressure. In both of the above cases, the program only needed the temp, pressure and humidity values, which were the same in each case, so the results should be the same.
The "use standard atmosphere" box does impact temperature. It looks up the standard temperature, pressure and humidity at the altitude you entered and uses those numbers, ignoring your actual temperature pressure and humidity entries. If this is the best option, it's by coincidence. There really isn't a good practical reason to check this box.
In your case, if you have a solution that works despite having entered incorrect pressure (29 and change absolute, when it should be 25ish), I would guess that it's because something else is wrong (probably velocity, but possibly other things like BC or range) and you got lucky. This is generally not a sustainable situation. You're better off in the long run getting every input correct rather than tweaking stuff randomly (canceling out errors with more errors) until it works. Out to 1000ish yards, the equipment we have access to (chrony's kestrels, etc) should be able to get you a decent solution with measured numbers. It won't be perfect, but it should be repeatable and understandable.
I have yet to come across a situation that wasn't fixable by nailing down the input numbers, starting with the most uncertain. If you nail the inputs to the best of your ability, you should get a decent solution. BC's are the toughest, because you basically have to trust someone (a manufacturer? your buddy? Bryan Litz?) to be accurate, and bullet lots change a bit. But I deal with that last - after everything else is known reasonably well. (Hint: go with Litz if he's got the data).
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To ad to the last post: COFOX and I are running very similar loads: 140's in 6.5cm with 25" barrels. His load is 42.3, mine is 42.4. I'm pretty convinced we should both be right around 2800fps... Using 29.92 inHg he's at 2850fps, and I'm 2875fps for our numbers to line up (that seems a little hot to me.. unless there's a really fast lot of H4350 going around or something). Using what we think was our absolute pressure (~25.00 inHg) for our altitude and temps the day of data collection, the calculator has us both down below 2750fps... Makes me wonder if the correct answer to all still lies somewhere in the middle...???
Here this might explain something on how we use things,
<iframe width="640" height="360" src="//www.youtube.com/embed/UVE6BVWPxGA" frameborder="0" allowfullscreen></iframe>
Also in the video, I have a bit of angle in FFS, so the solutions were off by .3, when I remove the angle they match up exactly. Coldbore using Barometric pressure, including the altitude and FFS using the Station Pressure. So doing it both ways you get the same answer. (as long as I remember to remove the angle)
It's really much simpler then you guys are making it out to be, when we shoot and use the computer, Altitude is a function of the barometric pressure, so using Station Pressure tells the computer where you are altitude wise.
It doesn't matter what you use, G1, G7, they both do the exact same thing, both need to be adjusted all the same, as even Litz's G7 are just an AVERAGE he measured with his rifles, not yours. All it means is he average will either work perfect or it needs to be tweaked to match your system a bit, same as G1, the whole, wrong shape is marketing. It's been modified, which is why it was used for 50 years before Bryan. It's the only G factor with a name next to it cause that guy adjusted it after the originator wrote the formula. If you want the best G Function, Band it ... put in different numbers for the different velocities as the BC will change as the bullet slows down, so Banding the BC works best. In some cases JBM will do it for you because that is a better solutions. Just do a sample track with a 175gr SMK and you'll what it looks like, pick the Non-Litz version and they Band it automatically. It's like a Custom Curve.
<iframe width="640" height="360" src="//www.youtube.com/embed/UVE6BVWPxGA" frameborder="0" allowfullscreen></iframe>
Also in the video, I have a bit of angle in FFS, so the solutions were off by .3, when I remove the angle they match up exactly. Coldbore using Barometric pressure, including the altitude and FFS using the Station Pressure. So doing it both ways you get the same answer. (as long as I remember to remove the angle)
It's really much simpler then you guys are making it out to be, when we shoot and use the computer, Altitude is a function of the barometric pressure, so using Station Pressure tells the computer where you are altitude wise.
It doesn't matter what you use, G1, G7, they both do the exact same thing, both need to be adjusted all the same, as even Litz's G7 are just an AVERAGE he measured with his rifles, not yours. All it means is he average will either work perfect or it needs to be tweaked to match your system a bit, same as G1, the whole, wrong shape is marketing. It's been modified, which is why it was used for 50 years before Bryan. It's the only G factor with a name next to it cause that guy adjusted it after the originator wrote the formula. If you want the best G Function, Band it ... put in different numbers for the different velocities as the BC will change as the bullet slows down, so Banding the BC works best. In some cases JBM will do it for you because that is a better solutions. Just do a sample track with a 175gr SMK and you'll what it looks like, pick the Non-Litz version and they Band it automatically. It's like a Custom Curve.
Here is JBM with the exact same data as in the video, it's different by .1,
JBM is Point Mass, and ColdBore & FFS are not, so they will figure things slightly different. I included the Banded BCs for you to see.
The one above is with Station Pressure the one Below is Corrected, Barometric Pressure, they are the same
Very easy, using Barometric Pressure with the altitude I checked the corrected box.
JBM is Point Mass, and ColdBore & FFS are not, so they will figure things slightly different. I included the Banded BCs for you to see.
The one above is with Station Pressure the one Below is Corrected, Barometric Pressure, they are the same
Very easy, using Barometric Pressure with the altitude I checked the corrected box.
OK, this is making a lot more sense to me now the more I play with it. The terminology between station, corrected, weatherman pressures was quite confusing!
My understanding now is:
If I enter absolute (actual at my pos) pressure, I do NOT need to enter an altitude, and this is NOT corrected (uncheck that damn box in JBM)!
By going this route, of putting in ~25.00 inHG, 0' altitude and a MV of 2,760 fps, that gets me real damn close to what I was getting in the field last weekend. I'm only off by +/- 0.1 mils, which with the way I was shooting, w/o knowing my true MV, w/o knowing the actual distances within +/- a few yards, I think it's pretty damn close! I'm going to call it a day!
Now, since I zeroed at only 93 yards, how bad does that screw me up? Also, I won't have access to JBM in the field next week, I'll be using iSnipe and it makes no mention of corrected, station or whatever pressure....it just asks for an entry. I HAVE to put in 2850 fps for MV, because if I try to use 2760, no matter if I enter 25 inHg or 29.92 inHg (both with or w/o an altitude), it's not even close to my actual DOPE! I have to put in 2,920 fps with 25 inHg to get close! That's not right...
Anyway, I think I'm ballpark now and will true next Thursday and maybe have access to a chrony by then as well. I'm going to go with JBM dope cards with 25 inHg, 0' ASL, 2,765 fps, uncorrected....and I'm going to buy me a damn Kestrel!
My understanding now is:
If I enter absolute (actual at my pos) pressure, I do NOT need to enter an altitude, and this is NOT corrected (uncheck that damn box in JBM)!
By going this route, of putting in ~25.00 inHG, 0' altitude and a MV of 2,760 fps, that gets me real damn close to what I was getting in the field last weekend. I'm only off by +/- 0.1 mils, which with the way I was shooting, w/o knowing my true MV, w/o knowing the actual distances within +/- a few yards, I think it's pretty damn close! I'm going to call it a day!
Now, since I zeroed at only 93 yards, how bad does that screw me up? Also, I won't have access to JBM in the field next week, I'll be using iSnipe and it makes no mention of corrected, station or whatever pressure....it just asks for an entry. I HAVE to put in 2850 fps for MV, because if I try to use 2760, no matter if I enter 25 inHg or 29.92 inHg (both with or w/o an altitude), it's not even close to my actual DOPE! I have to put in 2,920 fps with 25 inHg to get close! That's not right...
Anyway, I think I'm ballpark now and will true next Thursday and maybe have access to a chrony by then as well. I'm going to go with JBM dope cards with 25 inHg, 0' ASL, 2,765 fps, uncorrected....and I'm going to buy me a damn Kestrel!
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OK, I hear what you guys are saying. I'm just playing with COFOX's numbers in an effort to learn and understand as much as I can at the moment. I'm heading to the range Monday and will do everything I can to bring back some rock solid data. I'll be shooting at paper out to 1k at a high power range with perfect known distances, with Kestrel in hand, and I'll be writing down EVERYTHING! I appreciate you guys hanging in there with me this long. I still feel like hitting "calculate" on JBM is like pulling the arm of a slot machine. I still never know what is gonna happen! haha... I had a sense using the 29.92 was "lucky" and not sustainable. That's why I'm not giving up on this thread until I get to the promised land of "repeatable and understandable"!
You got it. I think you can enter 93 yards as your zero in JBM. Don't know about iSnipe. You're on your own there.
Thanks for all this Frank! I'm gonna go watch that video about 6 more times to let it all sink in. I hear ya: the basic concepts are not that complicated, but I still seem to get a mess every time I hit "calculate" on JBM! It is never obvious to me where the mistake is coming from...Gonna stay with it until I get this sorted out. Thanks for showing us we can go either way: Absolute pressure and zero altitude, or corrected with an on-site altitude input. Temp and Hum are always there... Edit: But you're saying the calculators prefer absolute pressure for best accuracy.
I'm gonna assume if I come back from the range Monday with solid data from CRC, there will be no more surprises. Gotta go reset my Kestrel! I guess my question would be: If I want to try to "true" with JBM, how do I know when to fiddle with velocity, and when to fiddle with BC to get things to match up?
In a match like the cup, there's not gonna be enough time to pull out the calculator and work towards a firing solution for each target. What kind of system would you use for a match like the cup? You wouldn't go in with only an electronic device, would ya? Would ya go in with one pre-made card? Or a couple based on expected temps and pressures?
What do you mean by "point mass"?
Those banded BC's are VERY slick! Where does that data come from? Published somewhere? Is that something I can easily track down for common 6.5 projectiles? Is that basically what a G7 is trying to do? -Take us one step closer to a banded G1?
Thanks!
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A rule of thumb is to tweak whatever it is that you have the least confidence in. So if you've nailed down everything else, and you're shooting 10 fps ES ammo, it makes sense to start thinking about tweaking the BC. It does not make sense to tweak the BC when you haven't even measured your velocity, because even the manufacturer's number is going to be better than no number at all. Make sense? It's like Whack-a-mole. Just smack down the largest uncertainty.
Point mass is just the mathematical method used under the covers by the calculator. It treats the bullet as a point in space, so it ignores rotational effects like yaw and spin. 99% of the calculators out there are point mass calculators. There are a handful that use other methods. But even two point mass calculators will differ slightly because they can be implemented differently.
G1 and G7 and banded BCs are a whole 'nother multi-page threaded can of worms you're about to open. It suffices to say they are different ways of modeling the drag characteristics of the bullets. They are all wrong, and how wrong they are depends on a lot of details. Out to 1000 yards, the difference is mostly academic.
I will go on record as saying that G7 is almost always going to be your best choice to start from. Others will disagree (I know this because we've had this discussion here a few times). In the end, it's a "how many angels on the head of a pin" sort of discussion.
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Usually you tweak the BC for longer range corrections and MV for shorter.
A single G7 number is the same as G1 it's just an average. The Custom Curve is more like Banded or Stepped, but only the Kestrel with AB uses the Custom Curve unless the Android App does too, I don't have an Android to say.
You can try banding on your own, figure most advertised BCs are for 3000fps so start there, then you can go 3000 to 2000fps and put in a lower number, then drop to 2000 to 0 and put in a lower number again. It would be trial and error, something for after the match. We have so much data for the 308 that is pretty standard. Though JBM might have the banded values for other caliber haven't checked.
I have personally gone to Trigger Time indoors, chronographed my load, hoped on a plane with that info and ran JBM for data and shot the match. Miles away and completely different conditions. The .1 or .2 difference is not enough to sweat. I shot the Grind in Oct with a rifle I never shot prior, zeroed on sight day before. Ran about 100 rounds through a chronograph at the train up, and doped it in the hotel. Came in 11th out of 90. There is a video on FB me shooting at distance with the Chrono on the rifle. From 0 to 100 then using nothing but JBM. I had post it notes for a dope card. ( no printer) took the numbers and matched everything up.
A single G7 number is the same as G1 it's just an average. The Custom Curve is more like Banded or Stepped, but only the Kestrel with AB uses the Custom Curve unless the Android App does too, I don't have an Android to say.
You can try banding on your own, figure most advertised BCs are for 3000fps so start there, then you can go 3000 to 2000fps and put in a lower number, then drop to 2000 to 0 and put in a lower number again. It would be trial and error, something for after the match. We have so much data for the 308 that is pretty standard. Though JBM might have the banded values for other caliber haven't checked.
I have personally gone to Trigger Time indoors, chronographed my load, hoped on a plane with that info and ran JBM for data and shot the match. Miles away and completely different conditions. The .1 or .2 difference is not enough to sweat. I shot the Grind in Oct with a rifle I never shot prior, zeroed on sight day before. Ran about 100 rounds through a chronograph at the train up, and doped it in the hotel. Came in 11th out of 90. There is a video on FB me shooting at distance with the Chrono on the rifle. From 0 to 100 then using nothing but JBM. I had post it notes for a dope card. ( no printer) took the numbers and matched everything up.
Conversation on here pays the bills, so people or me repeating myself is beneficial to my cause.
The more people who ask the same question, the easier my job is, lol.
Plus it gives me insight into those struggling with this and helps me craft a better solution.
The more people who ask the same question, the easier my job is, lol.
Plus it gives me insight into those struggling with this and helps me craft a better solution.
Scott, look forward to shooting with you at the Cup.
I'll have one, maybe two cards generated from JBM based on Fri-Sun forecast.
You best leave your I-phone in your car. If I see you looking at during the match when you should be watching for winds shifts....., I will smash it!
