help with ladder test analysis

[Milano]

Good evening,
I just started reloading for competition and have tried to do the Ladder Test at 200 yards. I have a brand new 6.5x47 Lapua and am trying to figure out how to load it for distance shooting of 600 yards or more hopefully. To briefly tell what I have done:
Full length sized.
I trimmed all my brass to 1.8360.
Uniformed the flash hole.
Uniformed primer pocket.
Weighed and sorted brass to within 0.2 grains.
Weighed and sorted the 142 gr Sierra MK bullets to equal weights.
Primed with CCI small rifle primers.
Then started at 38 grains of RE 17 loaded 3 to within 0.05 off the lands. I loaded 3 each time in increments of 0.2 grains of powder until I got to 41 grains of powder.
Set out a piece of plywood at 200 and started stooting. (I was cleaning between each shot for barrel break in.)
I only set 33 rounds down range because I could not find any desernable pattern or node (if my vernacular is correct). All the rounds impacted within the same 2 1/2 inch pattern. And all the sets of 3 rounds grouped to within 0.5 inch to 1.5 inches group sizes. (read: I could no longer make out individual holes because it looked like a close range shotgun pattern.) I am afraid of putting out the target at longer range because the velocity variation wasn't enough to think the rounds will climb up the target to find an accuracy node. (Velocity for the 38 gr was 2,624 es:36 sd:18. The velocity of the 40 gr was 2,797 es:18 sd: 9.)

Now the question(s).. what to do next? It seems wasteful to just willy nilly pick a load or two and run with it. Should I try Magnum primers? Take the time load another set and put the target out to 500 yards? Any ideas would be great and very much appreciated.

 

[4xforfun]

First off, what was said earlier.....break in the BBl first befor you test. Fire a few fowler/warm up rounds. with such a narrow window I might try .3 increments instade of the tryed and true 1% rule.

Now, back the hell up!!!!!!! I would do the ladder test as far away as you can....500...600 + yards. That is where the vertical starts to show up. Pace your shots...you do not want to get things to warm....say 3 or four fowlers and then 1 shot per min for the test.....keeping the bbl temp as constant as possible. I know the wind will move you around left and right, but we don't care about that. All we are looking for is vertical.. looking for those "clusters" of 2 or three shots that land in a groups (verticaly speaking)

I usualy fire two ladder tests at a time......3 fowlers and test from lightest to heavist....clean.....3 - 4 fowlers and work backwards from the highest to lowest charge weight. I use the same aim point for both tests.

Also.....you will need to be able to know what shot went where. I always have someone sitting down by the target with a pen and he marks the bullet holes after each shot. I use a red and green marker, one for each string.

Also....check this out if you havent already...

http://www.6mmbr.com/laddertest.html

Good luck.

 

[camac]

OK a couple of warnings on ladder testing.
1) Long range ladder testing no doubt works well for someone like Jason Barney who has low velocity spread in their loads (a bit different to 100 yard ladder test). If you are just starting competition loading, you velocity spreads may invalidate a lot of results so tread carefully. Your three shot extreme spreads of 36 fps will make it hard to discern small increments in powder changes. Interpret the results carefully.
2) As stated above you can only do this after your barrel is run in. Cleaning between shots, every three or indeed every 5 will have a large effect on velocity from shot to shot.
3) Also as stated above, the further out you go the better the ladder test works (as vertical spread becomes more discernable) but once again BEWARE velocity spread doesn't impact your decision. Unfortunately the further out you go and that velocity spread you get also acts more on the bullets point of impact. You have a chrony, so make sure you plot velocities alongside the powder charges. Remember ther is a stronger correlation between velocity and accuracy than powder charge. Accuracy "nodes" are generally a due to the bullet arriving at the end of the barrel between vibration nodes. Although powder charge can effect the frequency of the vibration, the time it takes to get to the end of the barrel (hence velocity and Optimum Barrel time)" is far more important. Similarly the further out you go, the bigger those velocity spreads impact on your point of impact.

From here the suggestions above (including your own) will work - just watch the velocity as well as powder charge so you don't make incorrect decisions. Don't be afraid to go out to 600 yards and as stated above forget the horzontal wind dispersion.

 

[jo191145]

Custom barrels usually break in in 5 shots or less IF everything was done right. I shoot 5 and clean good and they're usually ready to go. On the other hand I did have one custom tube that obviously missed the handlapping station ;D Coppered worse than most factory barrels.

Foulers Yes
One shot in .3gn increments Yes
No cleaning Yes

Vertical vs Horizontal

If I see 3 or more shots in tandem exhibiting tight vertical thats never bothered me. Shoot a couple groups and see if the vertical remains. If it does move the bullet .003"-.005" closer to the lands and it will usually disappear. Not always but usually.

 

[rocketron]

http://optimalchargeweight.embarqspace.com/#

not to add confusion but this works also

Ron

 

[camac]

Study Jason Barneys load testing closely. You will notice he has combined a ladder test with a round robin optimum charge weight (group) test. This is very sound data. Also look at his 1000yard 6mmBR test target -notice, if he did just one set of data it would be hard to get the correct information out. Look at 6 sets (essentially 6 shot group) and the data is much clearer. A single Ladder test string is very hard to use for long range load development. Jason's system is good or alternatively any round robin group testing at longer range or with chrony. Look for tight vertical and explore from there.

 

[Milano]

Thank you all very much. I was not expecting replys so quickly, this is great. I will use your suggestions and go from there. Thank you.

 

[Erik Cortina]

Did you see any pressure signs at 40 gr? If not, I would start from there and work up to about 42.5 gr., make sure you watch for pressure signs as you shoot. If you are planning on shooting 600 yards I would do the ladder test at that distance if range is available, if not, do it as far as you can where the mirage is not a factor.

 

[RonAKA]

What you are trying to do is identify a velocity range where the vertical point of impact is insensitive to small variations in velocity.

I see nothing wrong with three loads at each charge weight, and that may be the better way. However, you will need to do accurate measurements of every single shot. Pick a datum point, or aim point. Measure the vertical distance only from the datum to the center of each point of impact. Average that distance for the three shots in each group. Use a target for each set so you don't confuse the points.

Last graph the vertical distance of each three group average vs the powder weight. Then you may see a flat spot where increasing powder weight does not increase vertical point of impact. See this graph as an example which has a flat spot around 44.3 grains.

You could plot vertical distance vs velocity and put all the individual points of impact on the graph. In one way that is better, as velocity is the real variable of interest. However, there is error in velocity measurement, that can complicate things.