My Ladder Fell Down . . . What Now?

[rhubarb]

I've been reading about the ladder method of load development and decided I'd give it a try. The idea is to shoot a variety of powder charges starting low and going up and pick a load based on the vertical dispersion. Supposedly the rounds will string vertically and when you get a group of shots bunched together, a powder charge in or near the loads that produced that group will be ideal.

I loaded up 7 loads of .223 in Prvi Partisan cases trimmed to 1.751-1.753 with BR4 primers. The powder charge I varied from 24.2 to 26.0 grains in 0.3 grain increments and marked on the case with a magic marker. The powder was trickled up to weight. The bullets were Hornady 68gr BTHP. I shot my scoped 1:9 20" AR at 200 yards from a bench rest at 5 minute intervals. That's how long it took me to drive down and mark each hole.

Here's how it went with each shot noted in relation to the shot before it.
24.2gr Zero
24.5gr UP 1/4"
24.8gr UP 1-1/4"
25.1gr DOWN 2"
25.4gr UP 5/8"
25.7gr DOWN 1-7/8"
26.0gr UP 1"

I guess the good news is that they all went into 1.5MOA. Does that mean my rifle doesn't care how much Varget I feed it? Why would a load some 7% greater than the starting load shoot at almost the same elevation? I'm (pretty) sure it's not my shooting. What gives?

No, I don't have access to a chronograph.

 

[kelbro]

A case full to the neck of Varget with 68/69gr bullets is a pretty good load.

 

[flashhole]

Did you get signs of high pressure at 26 grains? If not, why did you stop?

When I do a ladder test I will usually have about 20 loads. I will do it twice and compare the two sets of results. It has always worked for me and I generally find the best results about a grain or two below max. Max is not always what is listed in the manual. If you have a reduced capacity case (thick wall brass) you can peak in pressure sooner than a thinner wall brass.

FWIW - my 223 loves a 1.9cc Lee Dipper Cup of Varget (listed at 26 grains).

 

[33rowdy]

rhubarb, I happened to do the ladder test today for my 270 WIN. In a nut shell I got nothing accomplished I wanted. The way it sounds is that you only shot 7 times or did you shot more?

What I do is label the box Speer 90 gr bullet, H380 powder. The boxes I buy will hold 50 rounds. I chose 4 rounds per weight. I'll shoot 4 rounds at one target with 55 gr, another target with 56, another 57 and so on. After every one of those 4 shots I clean the barrel. I take TC 17, brass brush, a jag, cleaning rod, and have a clean patch between every 4 shots with different loads.

Why I say "I got nothing accomplished" I'm blaming my Simmons scope I bought years ago that's cloudy and hard to adjust my eyes for, Also it seems that I have something internal coming apart because their is like a black dust of some kind stuck on the inside of the glass.

 

[rhubarb]

I stopped at 26.0 not only because it's the max per Hodgdon, but because a previous outing with Wolf SR primers showed serious pressure well below 26. The CCI primers fixed that right up.

I did only shoot seven rounds. I know it's a small sample.

Here's a drawing of the bullet locations. The thing that puzzles me is that the elevation, instead of steadily increasing, went up, down, up.

I'm planning a round with the extended OCW round robin next. Maybe my kids' mother would enjoy a day at the range tomorrow to show my appreciation on Mother's Day. I need to get a load lined out before my first high power meet next week. No rush, though. Practice is for people that ain't good, right?

 

[Hutch]

Has the rifle been proven out with some other ammo? It may be that the vertical stringing is NOT due to the powder charge.

 

[rhubarb]

With handloads, this gun generally shoots around MOA. Sometimes a hair under, most times a little over.

But it's more than vertical stringing. As I understand, the Audette ladder technique should induce vertical stringing. As the powder charge increases, the rounds should move up the target. In this case, the highest charge shot lower than the lowest charge. That's what puzzles me. Is that common or even possible?

 

[ClarkEMyers]

It's entirely possible - assuming consistent internal and external ballistics

(a real stretch given the extent to which conditions can and will change over half an hour - and I see no mention of wind flags or other common tools for bench testing at 200 yards)

there are any number of changes possible in a good rifle - barrel harmonics change see e.g. the Browning Boss device and the traditional technique of floating a barrel but adding a business card say in the barrel channel near the tip - not relevant to an AR but as an example of the principle and the principle is the reason for float tube on an AR - the SMLE has often been called a self compensating action as it is claimed the wibbles will compensate for the wobbles as the rear locking bolt and relatively weak action flexes.

Finally if it happened it must be possible.

My advice is to stay seated for the entire session of load testing and try to fire in the same condition rather than up and down and firing on elapsed time. If this means a spotting scope and push pins or pencil on a target or target image to mark shots then that's what it takes.

 

[madscientist69]

lower velocity allows more time in the barrel when it exits from a slower load the angle is higher due to recoil thus slower loadings grouping higher?
This is of course for the same zero and distance comparing two loadings,yes I know the overall trajectory should be different.

Is reasonable or just an old wife's tale when I started reloading.

 

[redneck2]

When I read about Audette, IIRC he tested at 300 yards to make sure there would be enough distance for drop of the bullet. Not sure that 200 is enough with something that shoots as flat as a .223.

Another thing I saw somewhere was to test each load in a rotation, shooting at different targets, one target for five shots per load. You fired round robin to account for differing barrel temps and wind conditions. IIRC, they recommended .3 grain variation. He was interested in which three loads shot closest to the same point of aim, then you could adjust seating depth, etc

 

[USSR]

I don't use the ladder method of load development for the following reason. In order to use it, you must shoot at a much greater distance than 100 yards and, at that greater distance, shooter induced error comes into play and separating that from your results becomes tricky. A far better method is to use a chronograph and look for a load which shows low ES and SD numbers in conjunction with small groups.

Don