Barnes 145 grain, .264" bullet.

[kilotanker22]

Anyone have a good G7 BC number for this bullet? I have been unsuccessful in finding one.
Thanks

[Unclenick]

Try 0.353. This is a conversion of G1 .703 at a velocity of 2700 fps. For Barnes loaded ammo, 140-grain bullets are going 2700-2735 fps. Most single-BC's of the G1 sort are given for typical muzzle velocities, so I grabbed that and ran it through the JBM converter. You can check with Barnes to see if that velocity assumption is valid. If not, you can rerun it at their evaluation velocity.

Even with the G7 only figured at the high end of the velocity range, it will be much more valid at lower velocities than that high velocity G1 will be.

[kilotanker22]

I would be interested to see what Barnes says. I am launching them at 2680 from my Creedmoor. Using the .703 G1, my bullets shoot higher than they should at 300 yards. But I have not tested again to verify that and have not had the time to shoot further.

Using the .353 G7 number you gave me and plugging the info in for my last range day, the new data is basically identical to my notes. Will be interesting to see how they shoot in the warmer weather. They shoot well right now, but with identical ammunition when the weather was a little warmer, my ES was far tighter. Coincidentally, the slowest round was the first fired and the fastest shot was the last in a twelve shot string. Dropping those two shots reduces my ES to 14 fps with a SD of 5. About the same as I get in warmer weather with the same load. Hoping this is just small primers not ignoring the powder as quickly due to the cold

[hounddawg]

according to this guy at snipershide .350, where he got that from or if it is good dope I have not a clue

https://www.snipershide.com/shooting...urner.6972614/

I am becoming a big fan of the Barnes Match burners, the 140gn 6.5's shoot great and I just ordered a couple of hundred of their 6mm 105's

[Unclenick]

They probably got it the same way I did, but using a different velocity.

The way it works is the bullet itself has a particular drag coefficient at any given Mach number. The G1 and G7 drag functions are given in tables of Mach number vs. drag coefficient for their respective reference projectiles. The BC in either system is just the number you multiply the reference projectile drag coefficient by to get your projectile's drag coefficient at the Mach number of interest. In this case, the standard atmosphere speed of sound is 1116.5 fps. The velocity I picked is 2700 fps.

2700 / 1116.5 = 2.418,

so I look for Mach 2.418 on both G1 and G7 tables. The ratio of the two will be the ratio of all BC's for the two drag functions at that one Mach number. The odds are 2.418 will actually fall between two Mach numbers on the table, and I interpolated, but the ratio in this instance was fairly constant over that range, and I could have used either of the bracketing Mach values.

The table of G1 and G7 drag functions near the Mach number of interest as cribbed from the JBM site's Downloads area:



Mach 2.418's BC's interpolated from the above table are:

G1 = 0.5464 and G7 = 0.2742

The ratio of G7 to G1 is 0.2742/0.5464 = 0.5018

If we multiply 0.703 by 0.5018, we get 0.352786, which rounds up to 0.353. So that's what the JBM calculator is doing when I use Mach 2.418.

The 0.85% different 0.350 number in the Sniper's Hide thread is what you get when you use a velocity of 2830 to 2876 fps, or Mach 2.535 to Mach 2.576 in the ICAO standard atmosphere. That velocity is higher than Kilotanker's. With a 6.5-284, you might well be there, though.

So the question remains: What velocity was used to find the 0.703 number? If Barnes will oblige, then we'll get the more accurate G7 number, though I have to point out that a 0.85% disagreement is going to be smaller than the difference you can get from changing powders or even just among bullets in the same box.

[ocharry]

Hi Kilo...
hey i will be the first to tell you i dont know what i am talking about, but i watched a guy on utube the other day "Trueing his data"

he was using a kestrel and the way he did it was he shot at 300 -500-700-900 at a horizontal line on the target. so the first shot at 300 was on the line but the other shots were high....kinda like you are saying yours are. he had a good velocity read ,,,,, kinda like you are saying you do..... so he was changing the BC to get things to line up.

he was adding to the BC number to get the data to line up with the dope -----when he got things to line up he was up a whole number on the BC. Went from 5 something to just over 6......so the way i read what he was doing is that the higher BC means the bullets real flight path is flatter than the original numbers indicate...so the up dope is less at the longer distance

not sure if i am reading this right ,,,, but---- the velocity and the BC go hand in hand so out of your gun those factory numbers could be all wet---close but not true,,,,im sure you know your velocity is true ------ so maybe just a tweek or two with the BC will get you to where you need to be so when you crank the dope it is running true with the data or what the bullet and gun are really doing

just read your post and i had just watched this just the other day so i thought i would chip in with something that could help you out.....or not but i did like what the guy was saying and it did make sense to me

i know you shoot a lot so this could be just another tool in the box for ya

anyway it is cold as the south pole here and if you are out shooting stay safe and warm--------- hope you can use some of this

ocharry

[Unclenick]

Ocharry,

Was he using G1 BC? It's a funny thing to see the error go what is usually the wrong way.

[stagpanther]

I am becoming a big fan of the Barnes Match burners, the 140gn 6.5's shoot great and I just ordered a couple of hundred of their 6mm 105's

I've had excellent results with the match burner in .277 as well.

[ocharry]

nick

not sure which he was using....or if he said, and i am not sure he said what cal. he was shooting either. or what bullet... i will try and find it and watch it again...think maybe 308...dont think it matters, true data is true data

i think he was just trying to show how to get the data and dope to line up so when he was shooting at different ranges his kestrel was giving him good dope at the different ranges

he did make a couple moves to get it to come together. but i am pretty sure if he did not get the data and dope together, from watching the video, he would have shot over the 900 yrd target with the original dope from the kestrel. the original data came from the ammo box ...vel and BC. he used the velocity numbers from the box and was only changing the BC to get the bullet to land where the kestrel said it should. and for everything past the first target the bullet strikes were high, and the farther out the higher the strikes. he did make a change at 700 i think, so without that im pretty sure with the original data he would have shot just over the top of the 900yrd target

he was just showing that the ballistics calculator in the kestrel and the data on the bullet may not work perfectly together, so, he was adjusting the numbers to make them match what the gun was really doing

i will try and find the video and see if i can post the link if you are interested

i thought it was interesting and since kilo said the data didnt match what was happening i thought i would post the info.....like i said i am surely no expert on this stuff....but i know kilo likes to wring everything out and i like reading his posts,,,,, and yours too but sometimes the technical stuff takes the fun out of it ...for me anyway....dont get me wrong i like making little group holes too. but i only need to know what i need and not the why. to much clutter for me and i way over think what needs to happen....i am just a shooter,,,,and this kestrel takes most of if not all the head stuff out of the equation for me...it does work for me.....just before it got so cold here i was out doing some yoting....the kestrel said 4.2 up .3 left.......375yrds....1 shot dead dog.....he never felt it

so for me when i turn on the kestrel and it gives me the dope to crank i want it to be the best dope it can give....or true data....i really dont care how it works....i want to hold it into the wind and point it at the target and tell it what the range is and it tells me my wind and elevation adjustments

i never had one of these things until about 4-5 months ago, i just have the model 2700.....not the real fancy ones. it only does one bullet data at a time..so to change it is simple ..and i have trued it some what ,out to 400, but the thing is amazingly accurate....as long as the info put in is correct...ie. true data

i know for me it makes the changes on the fly way easier than doing it in my wore out head or making a guess

just trying to help out

ocharry

[Unclenick]

Yep, I understand. Some want to be able to design cars, some just want to be able to modify and maintain them, and still others just want to be able to drive them. I think all technical interests have parallels to that, and they should. Nobody wants to expend the effort to get a graduate degree in a sporting activity before they can start trying their hand at it. Shoot first, and if the physics interest you, go for it. If they don't, ignore them and just shoot and have a good time. All are welcome.

I'd like to see the video if you can find it so I understand for sure what is going on. I know Kestral has had the Applied Ballistics app and the Hornady 4DOF app in different instruments, so I am curious whose solver is being used. Their 5700 series Elite models have a drop calibrator in them for correcting the curve fitting.

[ocharry]

Nick,

Looks like it is a 243 and he started at 500yrds and I think he used the G1

This is the link

Https://youtu.be/xFa2y73oNNY

I hope that works for you

Also it is from Masterpiece Arms

I also watched another video about this and this guy says out to 400 you should play with the velocity and past that the BC

I did it with the velocity....but I haven't been past 400 yet

Ocharry

[Unclenick]

Thanks for finding the link. I'll see if I can figure out what is happening.

[kilotanker22]

I can't wait for some more reasonable weather so I can actually do some testing
I need to get the velocity spread under control with this bullet and rifle. I am nearly certain that the cold weather and small primers are the culprit

[ocharry]

I am curious to hear what you guys think about what the guy says..or his theory

I know what you mean kilo....man it has been REALLY cold and snowy here

I got some new calls I want to try out.....the weather guy says its gonna warm up into the 20's late this week.....me thinks the votes will be out....they got to be hungry..lol...I gots sumpin forum...we will see

Ocharry

[kilotanker22]

Ocharry, I have not watched the video yet. I will do that now and let you know what I think

[kilotanker22]

His method seems solid to me. Verifying the velocity at a specific range and then adjusting the BC at further distances. This looks like something I would be willing to try. All he is doing is verifying his data and making adjustments based on the data he is obtaining from engagements. Quite literally what the term DOPE means

[hounddawg]

Getting the right dope is just the first part. The second is the matter of how accurate the scopes tracking is. If you paid $4500 or more dollars for your scope you can pretty much rely on it's accuracy. If you are like most of us do a simple test at 100 yards. That 2 MOA you dial in may really be 2.5 MOA or 1.8 MOA, you won't know till you test. All of my scopes are off by various amounts, none are dead on. This is no biggie if you know how much they are off and what you need to allow.

how to check your scope tracking

Scope Tracking: Tall Target Test | Applied Ballistics with Bryan Litz

I shoot out to over 800 yards and use only G1 BC's, it has proved to be pretty accurate to within .25 - .5 MOA. I test my loads at 200, 300, 500, 600, and 800 yards, and make notes. Then I make a small label on my computer which I tape to the inside of the scope cap. If I want to go from 600 to 100 to 300 then 500 I just look at the dope and adjust. No kestrel necessary. Life can be as simple or complex as you want it, I chose simple.

[kilotanker22]

Barnes said they obtain the BC at the higher end of the Creedmoor velocity spectrum.

They gave me a G7 of .350

[Unclenick]

Ocharry,

Two things about the video stood out right away; one is the author used a velocity determined on a different day rather than measuring while he shot on that same day. Velocity could have been climbing as his round count went up and the chamber got warmer. He needed to record velocities on every shot, or go back to the 500-yard target and sight setting with the last round in the string to be sure he was still on.

A second thing is he mentions about half a mil of crosswind he is seeing. That can be expected to give him half of an MOA of vertical POI change with distance, too (due to aerodynamic jump). I don't know where in the sequence of shots the wind hit that value. Which way the elevation jump0 goes depends on his rifling twist direction and the wind direction. For a 9:00 wind in a RH twist gun, the vertical change will be down. For a 3:00 wind, it will be up. Vice-versa for a LH twist barrel.

A small error he made is the factory's stated G1 BC for his bullet is 0.559 instead of 0.560, as he claims. But that small error would only amount to about 0.3" difference at 1000 yards. This bullet has a factory specified G7 BC of 0.287. The difference in the G1 and G7 prediction is about 4" at 1000 yards, or about 0.11 mil, which would account for part of what he saw at that range with the G7 trajectory impacting higher. Still, it isn't much of the total.

Another possibility that occurred to me is the scope he is using is likely calibrated in milliradian mils (3.438 MOA/mil) but the program could have been set to NATO mils (3.375 MOA/mil) without his realizing it. That would account for about 2/3 of a mil.

So, there are several possible sources of error in that test. I doubt we'll sort it out from the armchair, though. Just have to shoot to find out.

[ocharry]

wow guys...lol

ok first, dawg....you are right and that is kinda exactly what i do...for those quick elevation changes, but for the wind call, that is a kind of learned thing, sometimes i call it right sometimes not, and sometimes the wind where i am sitting and where the target is, is different...may even be a different direction but it is way easier with a good spotter that is making good wind calls....not so much at shorter distance....problem is with yotes, if you dont call it right the first time you very seldom get a second shot

nick, i thought he said he took his info from the ammo box?? and he did say he did this same test the day before each match, because of weather variance....i agree he should have went back to the 500 target just to verify that things were running true on both ends....and i asked that very question to him, his response was, " he did think about it but the video was getting long " for me that would be something that needed to be in the video....but i wasnt making it

i get it about the cross wind, kinda like a head and tail wind only not as bad...but same kind of affect

i havent had my kestrel very long.... i am still learning with it....but i do like what i see, so here is how i think it works...... when you set up the profile on you phone you tell it the velocity and the BC...you can use G1 or G7....the app has a bullet library with the manufacturers data on the bullet, there is a lot of bullets in there...my bullet was in there so i went with the G7 BC and it loads the bullet data...so then you tell it MOA or MIL and tell it to send...and it puts that data on the kestrel and the profile stays on the phone

my 2700 only holds 1 profile at a time....where the other 5700 and up hold 3 i think and they tell you a lot more stuff too...but the simplicity of the 2700 works for me...it is quick and dirty...no clutter to think about

anyway when you use it (2700) you tell it the yardage and point it into the wind for a read, and then you point it at the target for a bearing, push the button and it gives you a solution.....in the background it is doing pressure, humidity, temp, wind speed and direction (it has a compass built in that you calibrate on initial start up) so i would think the jump you talked about could be calculated too....not sure ....but it knows the wind speed and direction 1/4- 1/2- 3/4- full value and the target direction

all this stuff you said about the little differences i get ,, when i was working we called it tolerance stacking.....it keeps building until it dont fit

not sure what drag model kestrel uses but im sure they did their home work and it is as good as it can be

not saying the kestrel is the end all to shooting solutions... and the math sometimes makes my head hurt...do i think you need to know how you got there old school?? yep......but these new toys sure do make it easy to get there too and if the info you put in is right then it will give you a better solution ...i think... than just winging it... so i see where the truing can make a better ballistic model to use...as long as it is updated for the day you are using it....pressure, temp, humidity, air density, change so flight characteristics change...so change the numbers to make the ballistic calculations work seems logical to me, as long as they run true

you guys for sure have a WAY better handle on the math part than i do...and this toy makes it easy for me in the field to make good informed calls....not so much for the short shots but for the 400 yrd shots...i need all the help i can get for a small target

i do love this round table interaction with you guys...im gona get another coffee, you guys want anything while im up...lol

ocharry

[kilotanker22]

Ocharry, I am still fairly new to the math myself. In my neck of the woods, the hard part is finding somewhere to shoot past 300 yards.

I live 90 minutes from Williamsport, PA so I am buying a lifetime membership to the 1000 yard range there this year.

[hounddawg]

Ocharry for the wind, you are dead on when you say it is a learned thing. There is no device that I am aware of other than your own eyes that will tell you what the wind is doing between you and your target. Kestrels etc will tell you what the wind is doing where you are standing but ten yards in front of you the wind may be doing something entirely different. Make some low cost wind flags from plastic boundary tape and fiberglass driveway poles then set them out at 25, 50 ,75 and 100 yards and watch them for a half hour. You will see them blowing in 4 different directions at times

All you can do is practice, practice and practice some more.

best reading I have found on the subject

https://www.barnesandnoble.com/w/the...=9781510739741

[Unclenick]

The drag functions will be the ones from the BRL for the reference projectiles, so I don't expect an error there.

I have now posted a question to Masterpiece Arms. After running the calculations in some detail, I realized that his 500-yard point of impact is a perfect match to the predicted elevation change of 2.6 NATO mils, so his sight may be calibrated in NATO mils. But the Kestral is calibrated in milliradian mils, not NATO mils. My question to him is about the weather conditions the Kestral reported because the 2.64 moa come-up for 500 yards from 100 yards is too high for a standard atmosphere (2.56 milliradians in my ballistics programs). He would need pretty dense air for that in my software (32.6 inches of Hg on the barometer at 59°F), so we will see if he can report something about those conditions. I am thinking that for some reason the Kestral is exaggerating the come-ups a little, plus it is working in milliradians and he may be working in NATO mils on his scope. Maybe. We shall see what he says.

[ocharry]

kilo...i can do around 450yrds here at the house...i use 200 of that most of the time, hardly ever get under that...well unless my boy is shooting with me...we go down to 150...him and my grandson were out last fall and i had my grandson back at 200...he was doing really well...ahhhh, those young eyes,,lol

there are some places around here....farms...that im sure i could stretch out past 1000 but i havent asked....maybe this summer...but without a spotter it would be real hard...unless i have a really bid target so i could do my own spots or calls

dawg...i know exactly what you are saying about the flags...i have seen that exact thing you talked about-----the kestrel is like you said only good right where it is...at distance you have to make that call by what you see....wind ..mirage, in close 200 or so i dont really think about it to much unless it is really blowing...these 6.5 bullets seem pretty slippery and able to buck the wind pretty good

nick... i will be interested in what the guy has to say about your question...as for the kestrel ... i am pretty sure that it,,,if given good data will give you a relatively good elevation solution----- the wind however....even though the kestrel is giving you what it thinks or the algorithm or what ever it is doing may not be precise at distance....(it is probably pretty good where it is at) it is still a shooters call or his spotter for a wind input....and experience at making those wind calls only comes from doing it

also MY scope is a MOA scope....both turrets and reticle so i dont know if that really matters here just thought i would toss that out, but, i will say, i had NO idea there are two different mil numbers that need to be dealt with......how confusing that could be....kinda like having mil turrets and moa reticle or moa turrets and mill reticle......why in the world is that not standardized ...lol

this dang weather....jeees had another 5" of snow yesterday with a high of 12*...i am ready for spring i tell ya,,,heck 35 would be wonderful after the last 3 weeks

anyway ---- waiting to see what the response is from Masterpiece Arms

ocharry

[Unclenick]

Originally Posted by ocharry

i had NO idea there are two different mil numbers that need to be dealt with...

Try FOUR different mil numbers:

Warsaw Pact mils: 0.278 mil/MOA
Milliradian mils: 0.291 mil/MOA
Swedish Strek mils: 0.292 mil/MOA
NATO mils: 0.296 mil/MOA