The Ladder Method
The ladder method begins with the best estimate of the load, beginning on the bottom end of the load chart. The reloader loads sample cartridges in groups, usually five or six at a time. In each group, the load is increased incrementally. On the range, the groups are tested, one group at a time, beginning with the lightest load.
Keep the test groups small. When I test a revolver load, I use groups of six for a six-shot revolver. I save the little shipping bags from small parts and repurpose them for loads. I write the load info on the bag with a Sharpie and put the spent brass in it for later inspection.
It takes a little common sense to decide how large of an increment to increase the load, but it depends a lot on how much margin there is in the load tables and how accurately one can measure and trickle a particular type of powder.
For example, let’s say you are testing some .380 loads, and you are using Nosler 115-grain bullets, Nosler load data and Unique powder. On their data, the minimum load is 2.3 grains, and the maximum load is 3.3 grains. I use a Hornady Lock-N-Load scale for my quick check measurements. It is accurate to a 10th of a grain, so changing the loads among test groups in 0.1 grain increments does not make sense. Changing the increments to 0.5 grains doesn’t either since there is only a grain difference in the range for this powder. I generally use 10 to 15% increments for each group.
When testing loads, only change one factor. That is, if you are testing the amount of powder for a new load, don’t switch primers or case OAL in mid-stream. Use the OVAT (one variable at a time) method.
If a load you are testing is not the one, don’t keep shooting it. Use your bullet puller and move on.
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