EDIT
what am I looking for, excess velocity? to what level, 55g typically run around 3100-3200, would they be in excess of that?
You will be looking to see if the velocities you are getting are close to what the manual shows for that charge weight . There are a few things to consider when doing this though . First you need to know what the published data you are using , used in there test . What length barrel ? , cases ? , Primers ? COAL ? etc . The barrel length is the most important here really along with COAL . If they used a 20 inch barrel and you are as well then "in general" you should get close to the same velocities at the same charges . If you're getting 200fps faster velocities then the manual shows for a given charge weight . Then you're likely getting higher pressures at the same charges . So "in general" with all things being equal , you don't want to go to much over published velocities even if the book says you can go another 1.5gr of powder .
Now if there test barrel was 20" and yours is 16" . Then you should expect less velocity from the same charge . The opposite if your bareel is longer , you should get more velocity . Depending on the caliber ,powder and a bunch of other factors . For every inch of barrel gained or lost you should expect a 30fps to 50fps difference
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At what distance did you do your ladder test . 300 yards should be the minimum distance . This allows you to see the vertical stringing from charge to charge . If less then that , I don't see a reason for the ladder test .
The ladder test shows two things . What your rifles max pressure is for that load combo and should show at what charges that combo has a stable pressure node .
see this video
https://www.youtube.com/watch?v=yJKVc5z9WVM
For plinking loads , I'd not bother with looking for max pressure . If you're not showing pressure signs then you're safe . No need in finding "MAX" for plinking loads . You will not want your range loads pushing max because you're just putting more stress on the brass and likely reducing case life .
If you keep your targets , Which I recommend you do . Go back and see if you had a three charge weight spread that had a very small vertical string . That's likely a good spot to load a larger number of rounds and see how they group .
Also when running ladder test and or OCW test . There's a point in which you start playing with seating depth to tighten up your groups . Based on your OP I assume you're loading for an AR . AR's are not the best firearm to fine tune loads by adjusting seating depth do to the long jump the bullet will have no matter what . You almost always have to fine tune loads with powder charge , different primers or even changing bullets .
I say this because IMHO when working up a plinking load for an AR it's best to just do a tradition load development rather then these other types of long range accuracy tests . Just load 5 rounds each from published minimum to max charge weights working up in .5gr increments . You will almost always find one of those 5 shot groups will group better then the rest .