Very sensitive to seating depth

[ta406]

I have been having a hard time finding a good load for my 338 Edge. Last weekend I loaded up 12 rounds of 90 grains of H1000, CCI 250's with both Norma and R-P brass.
All groups fired at 200 yards

3 rounds of once fired R-P brass, 300g SMK on the lands - 1.10" group

3 rounds of once fired Norma brass,300 SMK .005 off the lands - 1.80" group

3 rounds of once fired Norma brass, 300 Berger OTM .005 off lands - 2.3" group

3 rounds of 8 fired R-P brass with loose primer pockets (I forgot to measure the neck tension but just the weight of the handle on my Rockchucker was almost enough weight to seat the bullets) 300g OTM on the lands - .650" group

Weird thing is that the last group with brass that probably should have been thrown in the trash was .650". I'm going to retest this load with Norma and R-P brass but I was wondering if any of you have experienced a rifle that was extremely sensitive to seating depth? Would .005 difference in seating depth make that big of a difference? Thanks in advance

 

[Dr. Vette]

I may be all wrong or interpreting your data incorrectly, but what I see is that you used two different types of brass and two different types of bullets, and shoot some loads with very loose necks, yet attribute the difference in group sizes to the seating depth.

Each brand of brass can have different capacities, yet you appear to have used them somewhat interchangeably.

Each bullet can shoot better at different seating depths, yet you appear to have used them interchangeably.

I would suggest that you need to deal with one variable at a time before making any presumptions as to what variables are affecting your loads. But, that's just what it looks like to me. Others may have differing opinions.

 

[ta406]

I may be all wrong or interpreting your data incorrectly, but what I see is that you used two different types of brass and two different types of bullets, and shoot some loads with very loose necks, yet attribute the difference in group sizes to the seating depth.

Each brand of brass can have different capacities, yet you appear to have used them somewhat interchangeably.

Each bullet can shoot better at different seating depths, yet you appear to have used them interchangeably.

I would suggest that you need to deal with one variable at a time before making any presumptions as to what variables are affecting your loads. But, that's just what it looks like to me. Others may have differing opinions.

Thanks. After rereading my post I forgot to include the fact that I had previously tested all but the last load with both virgin and fired R-P brass although it was the weekend before. This was the first time that I had tested the OTM's touching the lands. There was very little difference in the other group size's. But I see exactly what your saying.

After some thought, I'm going to repeat the test with good brass and the Berger OTM's, which is the bullet I'm more concerned about. I only have a few SMK's left anyway. I was just scratching my head at how a slight seating depth change made such a huge difference.

 

[Mikecr]

I agree completely with Dr. Vette.
And to your question of seating affects, yes it can have huge affects to performance.

While your seating adjustments may seem incredibly insignificant, they are actually a very coarse adjustment to load performance.
So the information you have so far may still be valuable. For example, you might decide that your barrel likes seating against lands(although I would test it with Berger's recommended seating test), and then move on to powder as a fine adjustment(incremental load development).

But go to one change at a time, like seating, with all else equal. Then go to the next stage.