.204

[247sniper]

Hi guys,

 

I know that the BC is advertised as .287 on the 20 call 39 grain SBK's.

 

Out of interest what are you guys plugging into you ballistic calculators to achieve your drop and windage, I am plugging in a BC of .220 to correspond with what my rifle is doing in real life.

 

What BC are you using fellas?

 

 

 

Steve.

[247sniper]

Thinking about it, this is not just with my .20 cal bullets. What do any of you guys use on your ballistic app when it come to bullet BC regardless of caliber, do you use the manufactures advertised BC?

[gbal]

Thinking about it, this is not just with my .20 cal bullets. What do any of you guys use on your ballistic app when it come to bullet BC regardless of caliber, do you use the manufactures advertised BC?

[247sniper]

Thinking about it, this is not just with my .20 cal bullets. What do any of you guys use on your ballistic app when it come to bullet BC regardless of caliber, do you use the manufactures advertised BC?

?

[gbal]

Thinking about it, this is not just with my .20 cal bullets. What do any of you guys use on your ballistic app when it come to bullet BC regardless of caliber, do you use the manufactures advertised BC?

 

Good question - you have to use something,but it is as well to be aware that the absolute accuracy,and comparability of manufactures' quoted BCs are not 100%,let alone the huge G1 and G7 issue,with G7 giving numerical values about 1/2 of the G1s.

No need for panic,as it will be fairly obvious,and most are still G1s,and you can compare within a manufacturer quite well eg SMKs in the same caliber,but different weights.Nor is the BC a constant necessarily across different speeds,even for the same bullet.

So expect some minor differences,as 'data' of somewhat differing comparability is sometimes being fed into ballistics programs,and the programs are themselves of somewhat different complexity etc,but still should be a big help,of course.

 

Gbal

 

 

 

 

 

 

 

[camo304]

Running Hornady factory 40gr 100 yard zero BC .275 chrono @ 3785 avg fps (3900fps quoted)26" barrel @250 yards= 10clicks and it seems on the money will have to see how it goes at greater distance.

[gbal]

Running Hornady factory 40gr 100 yard zero BC .275 chrono @ 3785 avg fps (3900fps quoted)26" barrel @250 yards= 10clicks and it seems on the money will have to see how it goes at greater distance.

 

That's fine so far.

Any discrepancies will be larger as distance increases,and may become fairly obvious if they are there.

Remember too the ballistics program is drop and drift,and will not have any allowance for all the other group dispersal factors that come into play,but the group centre will be good enough to check the program for drop and drift .

 

Gbal

 

 

[pork chop]

im running bullet flight on my itouch ,was shooting at 500yrd on sunday with my 204 using 39 gr bk @3650fps needed 25 clicks to get on target with a 200yrd zero.to make numbers add up had to set bc to .270 instead of .289 .these type of apps are good to get you some where on target but you cant beat pratice no real shortcuts i dont think

[camo304]

im running bullet flight on my itouch ,was shooting at 500yrd on sunday with my 204 using 39 gr bk @3650fps needed 25 clicks to get on target with a 200yrd zero.to make numbers add up had to set bc to .270 instead of .289 .these type of apps are good to get you some where on target but you cant beat pratice no real shortcuts i dont think

So true was watching my - the other week hitting gongs at 550 yards with is .204 but they were 10" we are going to try dropping to 4" at 550 next time. Think he was using a BC of .260 not the (.275 Hornday )

[Laurie]

im running bullet flight on my itouch ,was shooting at 500yrd on sunday with my 204 using 39 gr bk @3650fps needed 25 clicks to get on target with a 200yrd zero.to make numbers add up had to set bc to .270 instead of .289 .these type of apps are good to get you some where on target but you cant beat pratice no real shortcuts i dont think

 

 

That sums the situation up pretty well, especially using G1 values. The problem with G1 is that it's very speed dependent, and Sierra aside most manufacturers quote the highest BC value they get from any velocity - it may be one that your rifle and cartridge are actually incapable of achieving, never mind how much real BC reduces 500 yards from the muzzle.

 

Having said that, G1 and the manufacturer's quoted figure are usually more than good enough to get somewhere on the paper for target shooting at up to 600 yards. For 800 and upwards, an average G7 as provided by Bryan Litz plus a reasonably accurate MV figure are near essential if going straight from a 100 zero to 1K.

 

For the long-range pest shooter, there are two problems - G1 is all you get for the majority of bullets. And ... no sighters. If I were into this business, which I'm not, I'd very much want to get scope settings using targets at known distances before relying on ballistic programs, apps etc. Even if the rangefinder reads a different distance from those you've got settings for, if you know how far the 'app data' is out at say 500 yards from reality, you can factor that into a calculated setting for 450 or 550 yards.

[gbal]

 

That sums the situation up pretty well, especially using G1 values. The problem with G1 is that it's very speed dependent, and Sierra aside most manufacturers quote the highest BC value they get from any velocity - it may be one that your rifle and cartridge are actually incapable of achieving, never mind how much real BC reduces 500 yards from the muzzle.

 

Having said that, G1 and the manufacturer's quoted figure are usually more than good enough to get somewhere on the paper for target shooting at up to 600 yards. For 800 and upwards, an average G7 as provided by Bryan Litz plus a reasonably accurate MV figure are near essential if going straight from a 100 zero to 1K.

 

For the long-range pest shooter, there are two problems - G1 is all you get for the majority of bullets. And ... no sighters. If I were into this business, which I'm not, I'd very much want to get scope settings using targets at known distances before relying on ballistic programs, apps etc. Even if the rangefinder reads a different distance from those you've got settings for, if you know how far the 'app data' is out at say 500 yards from reality, you can factor that into a calculated setting for 450 or 550 yards.

 

As Laurie advises,and varminters like Ronnie have said repeatedly,even if you have QL etc,there is no substitute for checking your rifles actual performance by firing it at known ranges out to say 500 y.

The 'problem' is that we can be tempted to believe the BCs given by the manufacturers,as if they were like the bullet weights given.They are not-the weights can be checked,and will be found to be within a quite fine tolerance.The BCs cannot be checked by the shooter,and as Laurie,myself and others have indicated,there really is little check that they are comparable,or even very accurate,at your velocities.Brian Litz has established this for long range work,but it has some effect at any range,as Laurie says.

The problem is not strictly with the ballistics programs themselves,though they are unlikely to be very exact,but more in the data we feed in wrt BCs,which are not accurate enough,again ,just as Laurie says.

As a varminter,you can use the ballistics program and your data,including BC-it's the best you'll have,and see the drop,drift at specific distances.

Then you measure out those distances accurately,put up your target,and a rather large sheet of paper centerd on where the program says your bullets will land.fire some shots,and with luck you should be on paper,and can see where your POI actually is.

That is what your rifle does.So use that data.It will also give you invaluable data on group size,which is unlikely to be just pro rata with distance,for purely technical reasons,described elsewhere.

You might be able to juggle BC input to your balistic program to come up with your actual results.but why would you need to,as you have your rifles actual performance data,though you might try it for different winds etc.

There really is no alternative,and you owe it to yourself and quarry.It will pay off.

Gbal

 

 

 

 

 

 

 

[Crosshair]

You might be able to juggle BC input to your balistic program to come up with your actual results.but why would you need to,as you have your rifles actual performance data,though you might try it for different winds etc.

There really is no alternative,and you owe it to yourself and quarry.It will pay off.

Gbal

It would be really handy for me to be able to 'true' my Swarovski Optiks app as it then gives you exact distances for the ballistic reticle marks. Would modification of BC or MV be best to achieve an accurate model???

 

[gbal]

It would be really handy for me to be able to 'true' my Swarovski Optiks app as it then gives you exact distances for the ballistic reticle marks. Would modification of BC or MV be best to achieve an accurate model???[img=http://i144.photobucket.com/albums/r192/m18wilts/Snapbucket/B822242C_zps9dec1a4f.jpg]

 

Very tempting,of course and great if the ranges on the reticule were coincident with your actual fired shots.Does Swarovski not say what the reticule marked ranges are based on ie what bullet weight and BC and MV?

You could play about with BC of known bullets-has to be a bullet you can actually buy,and vary the MV within the achievable range and see if you get a fit,then load to that.Something like QL ballistics might make that easier.....

Gbal

 

[Crosshair]

Very tempting,of course and great if the ranges on the reticule were coincident with your actual fired shots.Does Swarovski not say what the reticule marked ranges are based on ie what bullet weight and BC and MV?

You could play about with BC of known bullets-has to be a bullet you can actually buy,and vary the MV within the achievable range and see if you get a fit,then load to that.Something like QL ballistics might make that easier.....

Gbal

 

You can pick from a wide range of factory loads or enter your own info. I suppose I can just test each distance in turn and make a note of the actual range (they supply a load of stickers for you to mark up as range cards) but obviously, being second focal plane, all the distances depend on magnification so having the power of the app to do the maths is very handy.

I guess I need to just get the real data and have a play around to see if I can find an accurate match either from the entire list of factory ammo or by adjusting MV/BC.

 

[Crosshair]

Actually, I've just had a closer look, and you can 'true' the BC in the app, but you need two chrono's to do it.

 

[Crosshair]

 

http://ballisticprograms.swarovskioptik.com/ if you want to have a play-its free.

[sonic]

Actually, I've just had a closer look, and you can 'true' the BC in the app, but you need two chrono's to do it.

Or less accurate average over one at two distances

[Crosshair]

Ok, so I downloaded iStrelok last night which allows you to 'true' based on actual drop at a given range. I didn't have much space this morning so I only managed to stretch out to 313yards but the actual drop was 2" less than the predicted 12" drop using Privi 55g sp.

 

According to the app, assuming the quoted b/c is correct, this means my MV is 300fps faster than that quoted in the Swarovski App at 3510 fps.

 

In due course, I'm gonna have a play with my 50g Vmax and my 62g Milsurp to see what their differences are but with any luck I've landed myself a fast barrel.

It's certainly not fussy- all three bullet weights shoot to the same 100y zero!

I really need a chrono now to see how close these best guesses are

[gbal]

Ok, so I downloaded iStrelok last night which allows you to 'true' based on actual drop at a given range. I didn't have much space this morning so I only managed to stretch out to 313yards but the actual drop was 2" less than the predicted 12" drop using Privi 55g sp.

According to the app, assuming the quoted b/c is correct, this means my MV is 300fps faster than that quoted in the Swarovski App at 3510 fps.

In due course, I'm gonna have a play with my 50g Vmax and my 62g Milsurp to see what their differences are but with any luck I've landed myself a fast barrel.

It's certainly not fussy- all three bullet weights shoot to the same 100y zero!

I really need a chrono now to see how close these best guesses are

Well some good news there.As has been said,do not rely on any data too much,if it did not come from your rifle/load:shoot and see.BCs are often 'at the best' velocity etc,and the affordable chronoscope was a big disappointment to the early wildcatters-it showed how optimistic their wonder velocities were!!

There may not be big POI differences at only 100,but they may well increase-try and see,as we don't know what the respective velocities actually are.Have fun!

gbal