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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