doing a Ladder test

Kevin Stenberg

Well-Known Member
I tried to find Waco's post on ladder testing. But was unable to. So here is my question.
Twice this winter i have done ladder tests on my 308 with 2 different powders. One powder was BLC2 and the other was H322. And i am completely confused! I shot about 25 rounds for each ladder with a .2 grain powder increase. All velocities were recorded (Magneto Speed Chrony) All velocities recorded on a graph to find any nodes.
Both ladder tests were straight lines from lowest to highest vel. You could put a straight edge ruler on all of the #'s and hit each velocity.
Yes i have none other tests and was able to find the nodes.
 

Pistolero

Well-Known Member
No two holes in the target were close together? All pretty evenly spaced vertically? How far away
were you shooting?

I believe the point is to find a place where different powder charges shoot to the same POI.
I don't think velocities have anything to do with a ladder test. Maybe I misunderstand it.
I think using the magnetospeed on the end of the barrel would invalidate the ladder test
due to the extra mass of the unit changing the barrel vibrations.

Bill
 
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Brad

Administrator
Staff member
Different ladder test Bill.
I too am more familiar with the one shooting rounds at 300 or so looking for a spot where powder charge increase doesn’t give vertical. Pretty popular with HP shooters as vertical is a bad thing at 600.
 

Pistolero

Well-Known Member
OK, educate me on "the other ladder test", I have no idea about it.

I would expect velocities to increase linearly, and in fact, every time I have done this sort of testing, it has
been extremely linear velocity vs grains of powder. But, I have never tried doing it in such
small increments, so maybe something different.

Bill
 

Rick

Moderator
Staff member
I mostly did ladder tests with 0.5 gr increases in charge and looked for the best groups with the best S.D., AV , ES. In half grain increments there is about a 50 fps velocity gain give or take, when the load reaches it's highest charge with that combination of components the average gain of about 50 fps will stop. That's normally not a max pressure load but getting close and additional increases in charge weight usually opens up groups.
 

Brad

Administrator
Staff member
Some people do .3 gr increases looking for a spot where velocity doesn’t change much with powder increase. Flat spots in velocity will likely give little vertical at longer ranges.
 

Rick

Moderator
Staff member
I'm talking about my magnum revolver and mid size bottle neck rounds, not cartridges like the 9mm or 45 pistol cases. A half grain could be a whole bunch there.
 

Ian

Well-Known Member
I don't do ladder tests. I stead I build a load combination around the intended purpose with a pre-determined exterior ballistic profile in mind and shoot 10-shot groups. By observing group shape and form I figure out what things need changing to improve it. Powder charge is only one thing that gets tweaked. My belief is that powder charge isn't in and of itself critical to consistency as long as the pressure is reasonably within the powder's happy zone. What IS critical is putting everything ELSE together in a robust zone that can tolerate some variables and not screw up the whole symphony. In the end it's all about harmonics and lots of things related to the cartridge can be tweaked to affect barrel time and harmonics, not just powder charge.
 

fiver

Well-Known Member
the ladder test is looking for a flat spot in the barrel whip.
pretty much what Ian and I are doing too, only we don't use the powder steps much beyond jumping up a bit for velocity then doing the actual tweaking through bullet jump and ignition sequence.
 

Ian

Well-Known Member
:headscratch:That's true enough Ian but the OP is about . . . . Ladder testing.
Yes it is, or more specifically, unexpected results with one type of test compared to other, similar tests. Fiver made a more clear thesis statement than I did, but we're pointing out the same thing: there are a lot of things going on that affect the objective of either kind of test (either timing the bullet exit to coincide with a pause in the barrel moment or finding a thermodynamic plateau with the powder charge) and it pays to also consider the big picture.

Eta, the mass of the magnetospeed on the barrel does murder to natural barrel harmonics and pretty much voids the results of any load work done using the target-based ladder test. That's one of the few disadvantages of the Magnetospeed.
 
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Intheshop

Well-Known Member
Just some observation Kevin,so don't take this as gospel.....

Most folks doing ladder testing are over "starting" loads. So if you are using reduced CB loads I don't know if the results are going to show up as dramatically...... which is akin to ladders at shorter ranges. The "noise" in the system at lower velocity and shorter ranges precludes the likelihood of the rounds coming together.

Also at lower velocity..... it's harder to hold tight groups in general as the range gets longer because of the trajectory. The arc really takes a parabolic form. That's not yo say you "can't" shoot tight groups...... think more in terms of betting. The odds are more in your favor to get the velocity up.
 
Reactions: Ian

popper

Well-Known Member
powder's happy zone IMHO this is where the chrony comes in, does fps flat out at the top of the curve? Along with ES - consistent burn?
 

Kevin Stenberg

Well-Known Member
Fiver was spot on in post #11 Up to these 2 tests. When i plot the velocities given per load on a graph. There is usually 1 or 2 spots with very low to no velocity increase between loads. An that is what i have read is a Node.
PLEASE if i am wrong. Enlighten me.
 

fiver

Well-Known Member
yep that's a node.
your looking for small zones where small changes in things like case capacity or slight powder weight differences are within an acceptable window of variance.
 

popper

Well-Known Member
My 2 cents - unless you are in a money game, makes no sense. My reasoning is - 25 shots of say 308, ~40gr/shot in 0.2gr increments over 2 gr = 250 shots @40gr/shot = 10k gr = 1.5# of powder. For jax, ~ 100$ spent. OK, now lets get into the statistical part. Use avg fps & plot the curve. Well, not exactly correct. Look at ES - is it greater than the difference in avg? SD is even more ridiculous! Point is can you really even find a 'node' much less several? Is your bullet & load/loading repeatable enough to have an accurate point? If you use the 'target' method is your shooting good enough to 'see' a node? I tried it with jax before I had a chrony - couldn't get good enough results to justify. Not against 'ladder' tests, just don't work for me. Will I work to get an accurate (for me) load? definitely. Terminal performance aces all other stuff. It's a return on investment problem. I don't sort cases, weigh bullets, trickle powder. Yes my jax loads are more accurate than cast but cast pretty much goes where I want. Does the barrel whip differently for different loads or the stability arc vary with difference to target? Probably, can I do anything about it? Probably not. Do my targets show a circular POI vs POA as loads vary? Yes, just compensate when hunting.
 
Reactions: Ian

fiver

Well-Known Member
the initial vibration is the firing pin hitting the primer and moving the case forward.
you can tune that.
now follow out the rest of a firing sequence.
powder burning.
case swelling.
bullet moving.
all of it is changeable.
and all of it changes when [how about not so much when but where in time] the bullet exits the barrel.
the bullet is being accelerated to pretty much the same speed every trigger pull [if you got that part of the deal correct]
the rest is just adjusting where the bullet is at say .2 microseconds after trigger pull.
 
Reactions: Ian

waco

Springfield, Oregon
250 Bullets? Pound and a half of powder?
It takes 10 rounds of ammo for the Satterlee load test. That’s it. It has worked for me and my brother the half a dozen times we have tried it. No targets involved. Just going off chrony numbers. Find the flat spot in velocity and that’s your load.
When I used this method to develope my high speed .308 load I never even shot the loads at 100 for groups. I just went straight to 500 yards and got sub 2 moa results.
I think it’s a very ecenomical way to work up a load. Very careful assembly of the rounds and a good accurate chronograph is all that is needed.