Thread: 6.5x55 SE Sanity Check

I’ve always been a group or ladder shooter when looking for new loads. However following Erik Cortina I would now look more closely at ES to zero in on the node.

Originally Posted by Dicko

I’ve always been a group or ladder shooter when looking for new loads. However following Erik Cortina I would now look more closely at ES to zero in on the node.

I like Erik's explanations, and I've cobbled together some form of hybrid method. First off I'm assuming Erik is correct with the charge determines the combustion characteristics (ES/SD) and the seating depth determines harmonics. It seems to me when developing a load your either going for precision or stability. Erik is obviously going for precision, where as the ladder/OCW test are looking for stability. I think with the small sample sizes using SD is preferred. If the samples sizes were larger ES would be preferred.

Using the 2209 data as an example:

Having thought about the data some more it looks like the best way to asses the loads for precision is using the mean ±2SD to estimate the ES for a given charge (IIRC 2SD should cover 95% of the probabilities). Initially it looks like 44gr may be good with the best ES of 17fps. However when using SD the estimated ES(eES) is 67fps. Choosing 45gr with the worse ES and tighter SD gives a better eES of 38fps.

Now with searching for stability like the ladder/OCW test, it seems the best assessment is to look at two charges next to each other. To do this I take the mean of the higher charge +2SD and subtract the mean of the lower charge -2SD. This gives attempts to simulate an under charge on a cold day and an over charge on a hot day (I don't know how much variance this will give but I think 0.5gr should be fair). The ladder/ocw method as I understand it would select the flat spot in the curve (either looking at velocity or vertical shift doesn't matter). This is 43.5-44gr. Using the above method this gives a shifted ES(sES) of 67fps. However the SD of 44gr isn't that great. Looking at 44.5-45gr even though it isn't a flat spot the sES is 63fps which is better.

One final caveat is because we are dealing with small sample sizes I think that the chosen charges will need to be verified. I don't know who said it but I tend to agree with: 3 shots with show you a bad charge not necessarily a good one.

As for my selected charges here they are in order of preference:
2209 44.8gr ~2790fps
2209 43.8gr ~2755fps
2213sc 48.8gr ~2640fps
2213sc 50.8gr ~2760fps

An interesting point I noticed there may be a shared node at ~2750fps with both powders.
Also if anyone has a better understanding of statistics please chime in (I'm not a statistician by any stretch of the imagination).
Let me know if this makes sense or is closer to the ramblings of a lunatic.