Seating depth.

[NF1E]

Working on tuning the seating depth of my 73 gn Berger bullets and precision bolt loads. After finding the powder load, now even more fun. Loading 6 each .010 jamb, touching, .030 off,.070 off and .110 off per the Berger reloading manual. Looking for that .030 - .040 wide sweet spot and then more refining. This is one of the most enjoyable parts of hand loading for me. Nice part of all this is once you change any variable, it back to the beginning. Whatta Hobby!

[KMW1954]

And the list of deviations is never ending! Like playing golf and looking for that one perfect shot that keeps you coming back or fishing and that one big trophy fish.

I am not one of those "Show me", I am a must see for myself.

[NF1E]

Excellent. A discipline that is almost impossible to explain to a generic loader. Makes for a very interesting and informative thread when others, of like minds, join in and share their journey. Whatta Hobby!

[CFJunkie]

Sorry to go full Nerd on you both, but I am anal about using data to make decisions.
Probably comes from being a systems design engineer for almost 50 years.

I believe that one can go down the rabbit hole trying to find what works best.
I'm particularly careful of making judgements with too little data.

With small sample sizes, one good group could easily lead you astray, and there are lots of variables that will create more group size dispersion than jump.
I would recommend being sure that all of those other variables are constant before attempting to make any decisions about what works best.

After shooting over 5,500 rounds with one of my .223s, I compared the performance of jumps for over 1,100 5-round groups.
Surprisingly, there was little change among jumps averaged over 0.010 differences.
Some of the best averages were far away from where I expected the best performance to be.
0.000 to 0.009 average = 0.277 164 groups SD = 0.053
0.010 to 0.019 Average = 0.274 271 groups SD = 0.053
0.020 to 0.029 Average = 0.284 226 groups SD = 0.057
0.030 to 0.039 Average = 0.286 43 groups SD = 0.061
0.050 to 0.059 Average = 0.293 23 groups SD = 0.066
0.060 to 0.069 Average = 0.295 36 groups SD = 0.054
0.070 to 0.079 Average = 0.284 19 groups SD = 0.056
0.080 to 0.089 Average = 0.282 37 groups SD = 0.064
With jumps well beyond what I thought would perform well, I got some of the best performance.
0.170 to 0.179 Average = 0.245 23 groups SD = 0.064
0.180 to 0.189 Average = 0.224 8 groups SD = 0.040
0.190 to 0.199 Average = 0.269 4 groups SD = 0.053
And even further out, I got another surprise.
0.210 to 0.219 Average = 0.261 15 groups SD = 0.066

For every test, I finally figured that unless I got a statistically significant sample at at particular jump I couldn't use the data to make any decision on what actually worked.

Considering that all of the samples had standard deviations among the groups in each listed sample were from 0.040 to 0.066, I would say that there is a range around each average that would cause a lot of overlap between the adjacent data, especially since the averages were generally so close together. Unfortunately, the number of groups in the samples around 0.170 to 0.199 and 0.210 to 0.219 were at the low range of statistical significance.
The number of groups in the samples from 0.000 to 0.029 were all over 164 groups with the upper two samples 271 and 226. But even with those samples the standard deviations were 0.053, 0.053 and 0.057 respectively, so there is a probability of overlap.

My conclusion is that other variables, like my "shooter induced variation", are masking what actually works best.
Fortunately, there are enough jumps that work reasonably well that I have decided to base my choices more on what bullet weights and what powders perform best before I consider specific jump choices.

For this particular rifle, in order of performance, the best three powders are Varget (0.261), N540 (0.266) and H4895 (0.271) and the best bullet weights are 73 grs (0.258), 77 grs (0.273) and 69 grs (0.277). All of those averages are better than the 0.000 to 0.029 jumps that I have always been led to believe produce the best accuracy.

[NF1E]

Wonderful information.
Not being any great calculator, I am just doing this for the halibut and trying to see what might appear to work slightly better. Only shoot on my own range these days and only against myself. Retirement is great. Whatta Hobby!

[charlie b]

One of the reasons I like using SMK's is their seeming indifference to jump. The Hornady ELD's are next up on that list.

But, the Berger's I've used like to be jammed. I do follow Berger's advise and test the jump in fairly large steps for first go around.

[NF1E]

One of the reasons I like using SMK's is their seeming indifference to jump. The Hornady ELD's are next up on that list.

But, the Berger's I've used like to be jammed. I do follow Berger's advise and test the jump in fairly large steps for first go around.

Hope to get out on the range with my latest seating ladder today. As simple as shooting a couple 3 rnd groups in each seating length might seem, I have always been able to find improvements using this method. Good enough for this old guy anyway. Whatta Hobby!