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Ladder Test Help?

 
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  #8  
Old 03-06-2007, 09:31 AM
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Re: Ladder Test Help?

The tests that start this thread have a basic flaw…

With most loads, there is a spread in velocity - say the ES is 50 fps. If we are working up a load in 0.5 grain increments, we might have a result like this...

Averages...

#1 = 2550
#2 = 2575
#3 = 2600
#4 = 2625
#5 = 2650
#6 = 2675
#7 = 2700

OK... load #1 does NOT mean that is the mean velocity of the load. The mean velocity of the load might be 2525, or 2575. Which is it?? We can’t tell with only one round.

If statistics are not in out favor, load #1 could be 2575 and #2 could be 2550, so it appears that load #2 is SLOWER than load #1??

"There is a decrease!!"

Or load #6 could be 2650, and load #7 could be 2725.
"There has been a radical JUMP in velocities, therefore there is a radical jump in pressure, or some other irregularity"??

The point is, you need a larger pool of samples, and 5 rounds is an absolute minimum to get an “idea” of what’s going on, and 10 rounds per load is MINIMUM to get truly accurate velocity, ES, and AV data.

Three shot groups are adequate for getting mean velocities to run ballistic drop programs.

One shot “groups” are not meaningful.

In the data above…

[ QUOTE ]
I tried a ladder test today with new 7 RUM. I was using Retumbo starting load at 88gr working up to 94 gr by .4 at a time.
Do you typically do this test at 300 yrds? Problem was that most the shots went into two groups with very little vertical spread. Here are the results:

1 3024
2 3003
3 3004
4 3083
5 3085
6 3084
7 3107
8 3108
9 3153
10 3143
11 3182
12 3200
13 ####
14 3218
15 3270
16 3269

I think shot 13 did not register. I was thinking shots 4,5,6 and 12,13,14. What would you suggest?


[/ QUOTE ]

Now analyze the data...

1 3024
2 3003
3 3004

#2 and 3 are LOWER than #1??

4 3083
5 3085
6 3084

#4,5,6 are 80 fps Faster than #1,2,3, and are the same velocity - hello??

7 3107
8 3108

# 7 and 8 are the same and only 16-ish faster than 3,4,5??

9 3153
10 3143

#10 is slower than #9??

11 3182
12 3200
13 ###
14 3218

15 3270
16 3269

#16 is the same as #15?? but both are 50 to 85 fps faster than 11,12,14???

What does this tell you... by the very nature of statistics, absolutely NOTHING! This pool of data has no information other than the gun shoots bullets and they come out the front. You can NOT draw any information from one shot ladders.

The reason is… the ES is much larger than the increments, so they overlap in both directions.

[ QUOTE ]

Test One FPS
1 89 2974
2 89.1 3093
3 89.2 3105
4 89.3 3130
5 89.4 3103
6 89.5 3125

Test Two FPS
1 92.6 3210
2 92.7 3235
3 92.8 3226
4 92.9 3245
5 93 3247
6 93.1 3252

Just for giggles I shot a 3 shot group at 300yrds with the 98.2 load. 1.16" or .38 MOA. Not that bad of group but the velocity was---3266, 3248, and 3223. Verticle was great, I misses a wind call!

[/ QUOTE ]

Note that the velocities are over and under the adjoining rounds.

This is a fine example of the deficiencies of the ladder test (for velocities or group analysis).

Nothing has been learned. If you go out and repeat the same tests, you will get totally different results… which mean that the results are meaningless.

.
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  #9  
Old 03-06-2007, 10:32 AM
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Posts: 877
Re: Ladder Test Help?

and thats point of impact is so important...
So far this week ive shot 2 ladders, with another coming on friday.
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  #10  
Old 03-06-2007, 07:50 PM
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Location: Oregon City, OR
Posts: 484
Re: Ladder Test Help?

Catshooter,
I appreciate you feedback, knowledge of statistics, and scientific background. I see the problem with the string of velocities that I posted. What do you think would cause this spread? Trust me I do not want to get in a ******* match being somewhat new to this site, but in your process of selecting a perfect load you do not account for any human error. Or I am I supposed to think that you would never miss a wind call or pull a shot. You might reject the perfect load based on human or environmental error. How scientific is that?
We each have our ways of loading for a new gun but in the past I have wasted to much powder and bullets trying to develop a load by throwing stuff at a wall and hoping something sticks.

I shot a 16 shot ladder. picked one load and shot .38moa at 300 yards. Without the information form the ladder I would have been wasting my time picking something out of the blue.
Like I said thanks for your response and I will probably load multiple rounds per weight next time to get some averages. It thinks that is reasonable advice.

AJ Peacock thanks for the direction.

Willys46
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  #11  
Old 03-07-2007, 03:08 AM
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Location: Michigan
Posts: 2,232
Re: Ladder Test Help?

Willys,

If you are not using uniform brass, you will get velocities to go up and down on a ladder. You essentially have 2 variables in your test 1) amount of powder 2) interior size of the case.

To eliminate the case issue, I always try to run ladders with once fired brass that has been prepped (uniformed, primer pockets, flash holes deburred etc.) and then sorted by interior capacity (brass weight).

By using brass that is very uniform, you are eliminating one of the variables. Your velocity spread should be smaller and the nodes easier to see.

Don
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  #12  
Old 03-07-2007, 04:54 AM
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Re: Ladder Test Help?

[ QUOTE ]
Catshooter,... Without the information form the ladder I would have been wasting my time picking something out of the blue...
Willys46

[/ QUOTE ]

Willys - if you are happy with the results, then you should stay with it.

.
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  #13  
Old 03-07-2007, 09:08 AM
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Posts: 484
Re: Ladder Test Help?

Thanks for the responses everyone. I will keep you posted on how it comes together.

Willys
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  #14  
Old 03-09-2007, 01:44 AM
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Join Date: Jul 2006
Location: AB, Canada
Posts: 555
Re: Ladder Test Help?

Hi,
Need your help guys...
I want to sort my cases by weight, and I have a strange situation.
270.5gr - 3pcs
270.8 - 10pcs
272.0 - 8pcs
273.2 - 9pcs
273.0 - 3pcs
274.5 - 4pcs
276.0 - 3pcs
Do you thing is a god ideea to group togheter the cases with the same grains (270.5 with 270.8), and 273.2 with 273.9
so on ... In another words not exceding more then 0.9gr.
I know the best groupyou can get with cases on the same weight, but I have to manny on this way.

Thank you.
Cris [img]/ubbthreads/images/graemlins/ooo.gif[/img]
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