Litz is nice....

Mush

Mush

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Now that I got everyone's attention. ;)

I went shooting long range for the first time with the new 338 lm.
Beautiful day, -7 degres, 0-1.5 mps wind.

My ar500 gong measure 40x60 cm.

Got back to 600 meters (the fartest that my pos Leupold Rx1000 tbr could range).

Inputed data in Applied balistic on the phone from the Kestrel 4500.

Dialed 3.7 mils up and 0.1 mil left.

I shoot 300 gr SMK at 820 mps.

First bullet hit at 1 cm at the bottom end of the gong.
I lauch another one to confirm and it missed.

Wtf ?

So I got a FFP scope on the gun and measure poa versus poi distance.
0.5 mil.
Put 5 clicks up and bingo...the bullets connect in the middle of the plate.

So how come my solution tells me 37 clicks and the reality is 42 clicks up ?

At home I rechecked everything in the balistic app.

Then I got the idea to change my bal. Coefficient from Litz G7 to the default G1 that comes in bullet library.

Wanna know the result ?
Bang....42 clicks....

How come a 0.5 mils delta between Litz number and the regular G1 at 600 meters ?

Can someone explain ?

Do some of you are able to work with his numbers ?

Btw, my gun and loads lauched bullets 2.75-3 inches apart. About .5 MOA.
 
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How accurate were your inputs? Velocity, scope height over bore, the environmentals? I've used the Litz based g7 in programs very successfully out to 1500 yes,but they are only as accurate as the input.
 
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If all that you did was change from the G7 model to the G1 model to get the correct solution, then the G7 given for that bullet is probably incorrect. The solution should not be that different at that distance between G1 and G7. Probably a typo when the G7 value was being entered into the library. I would inform Bryan about it so that it can be corrected.
 
The difference between g1 and g7 at 600m for a 338 is basically 0. You could shoot a wadcutter side by side with a 300smk and I doubt it would be half a mil off. Something else is going on here.
 
swissinn said:
The difference between g1 and g7 at 600m for a 338 is basically 0. You could shoot a wadcutter side by side with a 300smk and I doubt it would be half a mil off. Something else is going on here.
Click to expand...

Exactly. If I take Bryan's values for the 285 Hornady (doesn't have the 300 SMK on his site), enter all of Mush's data into JBM, then switch between the G1 and the G7, the difference is 0.7" at 600m in the solutions they give.

If the answers are not almost identical using the G1 and the G7 models, then one of their values is wrong. He could have other issues, but even so, the solutions should be nearly identical.

I don't have Bryan's book with me. But, the first thing I would check is if the values in the software match up with the values he lists in his book.
 
Keep it on G7
Does your software have the ability to recalculate your trajectory based on your actual drop?
If so use the setting and try different distances to see if you get the correct solution.
 
The muzzle velocity could be off by 300 fps. from what the bullet is really doing. The solutions given using the G1 and G7 models would still be nearly identical. BOTH would be wrong, not just one of them. The fact that they are giving different solutions tells you what the issue is.

The Applied Ballistics app was written by Litz, so both the G7 and G1 values in it should be his. It isn't like he's taking one value from Litz and one from Sierra.
 
Cappy said:
How accurate were your inputs? Velocity, scope height over bore, the environmentals? I've used the Litz based g7 in programs very successfully out to 1500 yes,but they are only as accurate as the input.
Click to expand...

My load is Av 2680 fps with Sd 2.8 fps and Es of 7 fps (not a typo). But was chronoed at -15 degree.
Scope eight was determined by puting a cleaning rod in the barrel through the action. 4.8 cm

The rifle is a TRG 42 , Near 45 MAO base and Near Alphamount and a SB PM II 5-25x56.

I am wondering why the same inputs but 2 differents profiles ended so far apart.
 
In the Applied Balistic app (near the same as Shooter) you can choose your bullet from the library. There is 2 entries for 300 SMK.

The 300gr HPBT MatchKing and the 300 MatchKing (Litz).
If I select the last one (litz) it then asked me witch drag. I choose G7.....HAHHHHHHHHHHHHHHH......this is were I goofed up !!!!!!!

Sorry guys I don't know how but I was using Litz table but the BC reported in the app was somehow still 0.748. That is why this is all ####ed up !!!

A second time, sorry ...

Now with the app setup good I get 43 clicks at 600 meter.

Thanks to those who tried to help me .

Mush
 
I loaded up this bullet in Applied Ballistics Mobile (Please confirm this is the app you're using) and it seems to be loading the correct G1 and G7 numbers.

The guys above are correct that at 600m there should be negligible difference between G1 and G7 based trajectory predictions. HOWEVER, if you select G7 and give it a G1 number (or vise versa) the difference is about 0.5 MIL which is the error you're seeing.

So I suspect that somehow you got the G1 value of 0.745 entered but have the G7 drag model selected and that's why the program underestimated the drop so much.

It might be possible that it somehow pulled the wrong value from the library, but when I just tried it the correct values were populated.

Nevertheless, I believe if you use the correct BC's from here on in you'll be fine.

.338 cal 300 SMK
G1 BC = 0.745 (average from 3000 to 1500 fps)
G7 BC = 0.381 (valid for all speeds)

Thanks Kris for calling my attention to this.

-Bryan

Edited: Don't know how I missed your latest post mush, but it seems like we're all on the same page now.
 
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BryanLitz said:
HOWEVER, if you select G7 and give it a G1 number (or vise versa) the difference is about 0.5 MIL which is the error you're seeing.

So I suspect that somehow you got the G1 value of 0.745 entered but have the G7 drag model selected and that's why the program underestimated the drop so much.
Click to expand...

Thanks Brian to come here and help.
I don't know how it happened but this the problem that I had.

BTW.... the thread title was only to catch and get as much help as could :) This is CGN style ;)

User error it seems.

Thanks you all
 
It is great that you not only got lots of help from very experienced shooters but Bryan himself addressed the issue, sounds like it is all sorted out now.

Maybe time to change the title of the thread?

Snapshot
 
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