Thread: Interpreting a Ladder Test

Originally Posted by Puffin

Attachment 22584

Hi P38. To make it easier for me I numbered your shots. Statistically there are no patterns here, just data that says that ladder testing will not give you the information you are wanting.
Both ladder testing and the OCW method are intended to identify barrel vibration "nodes" as a means to reducing the effect of shot-to-shot variance in a given ammunition. My interpretation of this target is that other factors in your set-up are setting the overall group size, masking the information that the ladder test may otherwise provide. They will do the same thing for OCW testing.
My best advice if you are wanting to shoot smaller groups is to pass on ladder & OCW testing and shoot test groups with each type of bullet that are acceptable for the task you have in mind and hope that one or more of these meets your expectations, sticking with a moderate load for each, 7-shot minimum groups to get a bit of statistical significance. Good luck.

Puffin

Thanks for this.

I agree the ladder test really didn't tell me anything at the end of the day and the OCW may be too much at this stage.

However I like the look of the two loads I shot groups with the following day.

I'm using this load for hunting at moderate ranges, up to 300m.

I have access to a 200m range and will retest these loads in a week or two shooting some groups.

Cheers
Pete

I was trying a new powder for my .280 and every load from 53.5 to 58 shot into a 2" group the next 2 at 58.5 and 59 moved away appreciably, so I'm going to load 3 at 57, 57.5 and 58 and hopefully get good speed and a smaller group.

Two good things about 3-shot groups; they are cheap, and you're 30-40% through shooting a meaningful number of shots to draw some valid conclusions. Either or both of the 47.5gr loads may shoot very well as you say, and if it was my rifle and load development my next step would be to make those test groups you have planned 10-shot groups of each (same number as used in the ladder test) to confirm this and to see if one of these shows through. If you do please post and let us know.

Three-shot groups are popular. I know this. I don't mean to appear to be down on your efforts either. From personal experience drawing incorrect conclusions (not helped by insufficient data overlayed with some wishful thinking ) is a path to wasting a lot of time and ammunition further down the path of load development, something to be avoided.

Pick three of the shots at random from your 10-shot ladder test. Repeated sampling like that will show up a fair % of these samples as small groups. It says something about what sample size may be required to give an insight into the true "population" doesn't it ?

Some good points raised above. I would be testing the good grouping loads from 100yd at the intended range of use on paper from a solid rest.

Ladder test is well explained here;

6mmbr.com

Today I tested what I considered the most promising load.

I have settled on 47.5grs of W748 at this stage. Testing out three different 150gr projectiles, Horandy SST, Hornady Spire Point & Privi Partisan Spire Point.

I loaded up 5 rounds of each and shot 3 shot groups at 200m with the following results.

Each of the groups look ok to me but I can't explain the POI change as yet except for each was a different type of projectile.

I'm confident I can take any of these hunting but would like to see how much better I can get them.
I was using a 300m sight in target and each square on the grid is 35mm (nearly 1'1/2)



Cheers
Pete

Pete, what I was angling at previously is that a 10-shot group with one of these projectiles and at one powder charge - say 47.5gr - would likely look something much like your ladder group - I don't think it would be that much smaller just because the charge was fixed. That is representative I believe of the current rifle/shooter/set-up combination. I'm drawing this conclusion because the ladder pattern with what were small changes in powder charge has the appearance of being completely random. The more recent groups at 200m also look (within the limitations of 3-shot groups) to be representative of this level of precision. Different bullets will have different profiles, materials, tolerances etc. so the POI movement with bullet type doesn't seem unexpected, I'm not sure I'd be concerned about that. My assessment is that the rifle/shooter/ammo/set-up is currently 2-3 moa capable, and this may be fine for what you want it to do. If not, then begins the tricky path to finding the contributions that are setting the precision, ideally from the most significant, fixing or improving, and work down the list. I would be inclined to put exact powder charge down the list though. Just my opinion of course. If you plan to stick with your current barrel ( a new True-flite UM fixes many things! ) then continuing to try some other bullets and powders may bring results? Is the barrel copper fouled? If all else fails do much lighter loads shoot better? They often do in my rifles - I'm picking because recoil is an excellent destroyer of consistency in shooting!