How much difference does it make at 300m if I uniform a primer pocket in Lapua 6BR brass?In the video below it was showed that group size of primer uniformed vs. not uniformed does not differ in a statistically significant way.
The thing about tests like this, is the actual quality of his brass pocket depth average and scatter. It is too easy to draw bad conclusions on poorly designed tests. Sorry to be critical, but just posting on YouTube doesn't qualify the results as valid and that spread of charges detracted from his test.
For example, what was the variation in this brass to begin with, both in terms of the average and the scatter? Why spread the test over a range of charges when what you are testing is supposed to be the pocket depths?
Knowing when to uniform is more important than told. The average depth is less important than the scatter in the depth. You can compensate for a batch to batch drift in average, but scatter is different.
His system of running all those different charges adds to confusion rather than clarity in the test and robs him of getting more samples into the places where they count.
A pocket depth uniform versus not uniform test would look like his best powder/bullet recipe with the best tuned group with any given primer for a baseline. Then show the pockets sorted after inspection for the highest variations in depths versus ones that have been uniformed or sorted for the least variation.
If the test is all good pockets versus better pockets, and spread across charges in and out of tune, it is weak. Distributing the few samples against multiple loads going in and out of tune, just adds to the confusion.
Concentrating the results to leverage the stats and arranging to either sort or force primer pocket depths into variation would have made the testing worth the effort.
You know, it is possible to intentionally force primer pocket depths into a scatter by using a tool, rather than wait for several batch sorts to save them up. Not every system will shoot the difference so you need to wait for the right gun and have a good tune, but you can force the brass into "bad" with an adjustable tool rather than wait for multiple batches of brass to come through your bench.
Before you get the impression that this is easy, there is debate as to seating method. Forced to the same depth regardless of pocket depth, versus always pushed to the bottom of the pocket plus preload crush for example. Pick your poison.
To make up a decent test, intentionally cut a three to five mil variation into the pocket depths, make it at least 10 to 15 of each extreme depth so nobody can say you are under sampled, pick one depth as a baseline and make 15 of those for the baseline group, then seat primers to a fixed method.
It is also good to show the seating depth results and method since some of the methods used to seat primers are better than others. Then see if the groups made of a mixed set of both extremes of 3 to 5 mils shoots as tight for you as a group made of baseline ones with less than 1 mil of scatter.
As you can see, not a fun or cheap task, and you need to have a rig that shoots small with reliability as the test mule too. Sorry for sounding critical of BoltActionReloading's test, but it didn't prove anything one way or the other. YMMV
