Seating depth variation

[VenatusDominus]

With my .223 I fired a ten shot group at 100 that was 7/16". Then I did it at 200 yards and the group was 7/8". If I fired twenty more at 100 and 200 respectively, would the groups get bigger?

Likely, but probably not by more than 30%. From a statistical standpoint, data on a bell curve usually starts to stabilize between 30 and 50 data points and after that you are simply filling in the curve between +3SD and -3SD. You have two ten shot groups at 7/16 MOA. The group would likely grow in size slightly as you increased the number of shots but not likely to go from 7/16 MOA to say 3/4 MOA. What shooting 30 at the same distance and aim point (in smaller strings allowing the barrel to cool between) provides you with a mean radius. If your group size is 1/2 MOA, the mean radius may be 1/4 inch or smaller, meaning 50% of you shots will hit a 1/2" target at 200 yards. You can then figure out 1 SD and know that 68% will hit within that radius and 95% within a 2 SD radius.

 

[Ckleeves]

I have spent quite a bit of time playing with seating depth and I'm in the camp that it doesn't make a huge difference (somewhat bullet dependent). I used to be a believer and would do all sorts of seating depth test and after "narrowing it down" in .02 increments would go as small as .003 increments. If you take the best and worst seating depths and load/shoot a large sample size of each the results have surprised me. There might be a difference but (most of the time) it's not going to be near as large as many would believe.

It's just like .2 grain powder changes making a difference, do the same test 10 times and you probably won't see the same results twice.

 

[bamban]

Digest this for a moment. Rounds were loaded to fit in magasine. 300WM, 190 SMKs, 2 test barrels each fired 14 five shot groups at 200 yards. That lot most likely accounted for lots of people on the receiving end instant dirt naps.