Ladder test

[taliv]

no real point here, just an imperfect example, shot today in the rain. obviously doing a ladder test at distance gets polluted as barrel harmonics and drop get mixed together, but i did it anyway, for no good reason.

I loaded 10 rounds very meticulously starting at 43.00g and going up by .10 exactly each round (except i'm an idiot and skipped 44.50g)
Then i shot them in order starting from 43.60 and going up, then going back to 43.00 and going up. I was having trouble seeing the cluster of holes on the cardboard so i couldn't tell exactly which order the last 5 rounds were shot in. I think I know, but I'm not 100% sure so I just put them all together with their velocities. Also, I did not change my hold at all, including no compensating for wind, so i believe the horizontal is mostly wind.

Couple interesting points...

IME, when you get close to the max, a LITTLE bit of powder will make a BIG difference in velocity. But back off a few grains and changes in powder don't produce nearly as large an increase in velocity. During matches, I'm usually shooting these more than 100 fps faster. This is a pretty moderate load so you can see it doesn't change that much. In fact, for the 5 rounds from 43.60-44.00g the velocity varied only 8 fps. and only 3 fps from 43.80 to 44.00. Of course, with a sample size of one... and I don't have an explanation for the next 5 shots which are all over, though my eye was getting a little fatigued so i let a couple of them sit in the chamber longer than a minute while i blinked and tried to focus.

another interesting note is despite varying the charge by a whole grain from 43.00 to 44.00, the 10-shot group was still sub-MOA and the vertical component is only 1.33" at 331 yards, which is well under .5 MOA

according to jbm, the min and max velocities 2832 fps and 2901 fps should give me drops of 13.9 and 12.9 respectively, so exactly 1" vertical at that distance, ignoring bullet exit/barrel harmonics.

shots 2 3 4 look pretty tight, 5 fps and only 2 bullet diameters of vertical. i'll make a few more of those and see if it is repeatable

 

[Blue68f100]

Shooting 1 round at a load will not tell you much of anything. Need a min of 3-5 to even get a average. More points the more accurate you data will be. Then since you were only changing the charge 0.1gr is not much at all for a rifle. The only reason to do a small change like this would be once you found your best load is to work on each side to fine tune.

At least you got some trigger time.

btw. Not bad shooting at that distance.

 

[Sunray]

Like Blue68f100 says, the "ladder test" really tells you nothing at all about how well a load will shoot. Only tells you approximately where that bullet hit in relation to the others fired that day.

 

[taliv]

i think one round will tell you quite a bit. it's not perfect of course

Like Blue68f100 says, the "ladder test" really tells you nothing at all about how well a load will shoot. Only tells you approximately where that bullet hit in relation to the others fired that day.

heh, how well a load shoots IS where the bullets hit in relation to the others

 

[WestKentucky]

I disagree that one round tells you nothing unless you are not looking at the cases for over or under pressure signs. One shot tells you where the shot will hit relative to where its zeroed currently...it tells you nothing about repeatability. One shot may hit bullseye with a single shot but have a huge spread in a pattern, or one shot could shoot 15 inches off but be a 1 inch 500 yard gun. The brass will likely tell that story as the primer gets more flattened the rounds usually gain consistency...when primers are not flat for any reason accuracy tends to suffer

 

[mugsie]

Was this 6.5mm?

 

[taliv]

yeah 260AI

 

[gojones]

Have done something similar to narrow down my starting load for more extensive testing. Usually 5 shot groups of each load. Once I find the load range where the impact are closest, I use this as the starting range. It does not always give me the tightest group but in most cases I have noticed that my tightest group will lie somewhere in that range.

 

[Laphroaig]

^ +1

I think that's what the ladder test is designed for. It tells you something (what loads agree with the barrel harmonics of your particular firearm) but not everything. Once done, you need to fine turn your load within the nodes you find with the ladder test.

Chronograph velocities are for general information only at that point.

Laphroaig

 

[oldfortyfiveauto]

I typically shoot 8 shots equally divided between the min and max charges. If I get at least 3 rounds with little vertical spread between them I load some more at the midpoint of those for trial groups. No point in wasting rounds or barrel life on loads that don't show any tolerance to load variation.

 

[taliv]

just for grins i repeated the test again on the same piece of cardboard, just the 5 shots from 43.60-44.00 today from 529 yards. i couldn't see the holes from that distance so i don't actually know what order they're in, but the groups are sized and shaped remarkably similarly with one low and 3 almost completely horizontal. wind was blowing from the other direction today though. (again, i made no adjustments for wind)

hard to read the calipers but it is about 1.8" of vertical and 2.5" total, so still 1/2 MOAish from 500+ yards

 

[Laphroaig]

That's some nice shooting. Especially considering the distance and difference in powder weights.

I guess that it won't be necessary to weigh charges with that combination.

Laphroaig