NooB Confusion

[Rescue]

New to reloading and trying to figure out how to find the correct seating depth. I have a pretty accurate load working with a CBOL of 2.550 but it groups about .5 MOA. I was told by a fellow shooter that adjusting the seating depth .002 on either side of my best load is the way to find the "sweet spot".
When I consider that I can load five sets of test loads that vary only .002 I'll have about .012 difference from one end of the sample set to the other and when I look at .012 on the jaws of my caliper it seems ridiculous to expect to see much difference between successive loads.
Is my friend correct or is there a more dependable method for finding the best seating depth?

 

[Sniper338]

Do some research, theres ways to find a good starting seating depth. Personally I find my good starting seating depth then test loads... when I find the right powder charge it loves and all I will tweek with seating depth. Yes a thousanth can make a difference.

 

[mao0720]

Your friend is correct, .012 and even .002 can make a significant effect on accuracy. They way I usually do is: I do my initial load work up with bullets jammed into the rifling. I do this so that I know that I am working up my load in a scenario that requires the most force (and pressure) to start the bullet on its path down the barrel. That way one I start doing seating depth tests I know I wont run into a spike in pressure because I will only be moving away from the lands. It also makes it easier to do seating depth test because you only hve one direction to work. OK, so I do initial load development with bullets jammed into the lands. Once I find a good load, I test 4 groups for seating depth, these are original measurement, jammed into the rifling, .040 shorter, .080 shorter, .120 shorter. This is a modified version of what Berger Recommends. One of these groups will usually be significantly better than the rest. I then load 3 groups shorter than that and 3 groups longer than that best gross seating depth. I load these new groups in .003 increments. I then make my decision for seating depth based on this final test. If there is no conclusive evidence for a best group then I reshoot.

 

[mao0720]

BTW, if .012 looks small to you, get familiar with micro measurements. .001 can have an impact on accuracy and safety in certain measurements. Get used to measuring small. Measure precise powder charges (to less than .1 grain), precise seating depths (to at least .001"), and precise neck thickness (to .0001). Precision in loading leads to precision in shooting.

 

[LHSmith]

In short range Benchrest, most make seat depth changes in 0.005" increments. This is the amount that most have observed a noticeable change that is repeatable on the target.

 

[LHSmith]

BTW, if .012 looks small to you, get familiar with micro measurements. .001 can have an impact on accuracy and safety in certain measurements. Get used to measuring small. Measure precise powder charges (to less than .1 grain), precise seating depths (to at least .001"), and precise neck thickness (to .0001). Precision in loading leads to precision in shooting.

Depends what type of shooting the OP is testing for. For the record, most 100, 200, 300 yard benchrest matches are won by shooters who throw powder charges from measures that yield +/- a tenth and a half grain accuracy ( 0.3 gr. total variation in powder charge).
Ones ability to read conditions one shoots in will have a far greater effect than holding to those tight parameters listed. However, if producing ammo dimensionally to that level of precision listed will build confidence by all means go for it. Also, most veteran reloaders will have trouble getting consistent instrument readings when measuring to one thousandths of an inch, measuring to a tenth with repeatable results will leave a lot of newbees discouraged.

 

[joshb]

"Once I find a good load, I test 4 groups for seating depth, these are original measurement, jammed into the rifling, .040 shorter, .080 shorter, .120 shorter.
[/quote]. I have to comment, here, and say "be careful". Pushing the bullet back "a lot" can reduce case volume and create higher pressures. A while ago, I pushed back .16 to try a "warm" load of Varget at mag length for my 308. Not a pleasant experience.

 

[Erik Cortina]

Test in .003" increments, you'll find a good load. I like to test from .010" jump to .040" jump.