Seating depth

[NullMac]

I kid you not
Five shot group shots 1 and 3 nearly through the same hole the others all over. And for comparison three shots near through the same hole with factory ammo

I believe you, that's not seating depth that's the problem.

 

[Bowland blades]

As an exercise in expanding your knowledge of reloading, its worth taking some std cup and core SoftPoint bullets out of different boxes , same brand /type /weight. Then take your calipers and your bullet gauges ( hopefully people aint so naive as to measure tip to base) and simply look at the tolerances .
It will surprise many.

 

[Alantoo]

Thank you all for your comments and thank you Alan for the explanation and picture showing how the seating depth can change the group sizes.

Having just reread the thread, I realise I had misread your OP 5” as .5” so thought you were looking at an initial range of 0.5" to 1.5”

I agree with others a 5” spread looks significantly more than a seating issue, and significantly more than an inadvertent load variation issue to me.

It would be interesting to see if you can reproduce those results. But I would imagine there is something else going on.

As far as my target goes, don’t put too much store in the apparent graphic relationship of seating value to group size. Until I have done a few more groups to confirm it was not just the random variation and / or shooter error I am only drawing the conclusion that the load is pretty good. The average POI is in much the same place as my current hunting ammunition scope setting. If you superimpose all the groups with that load and bullet it would make for less than 0.850” for a 15-18 shot group that is irrespective of seating depth.

I like the salutary observation that fliers can go in as well as out! So I only ever assess by my worst group size. If you consider the bottom left group which has the minimal variations of seating depth but a significantly different group size, that is the tell tale.

Alan

 

[ChesterP]

The last time I saw a 5 inch spread, it happened after the first 5 to 6 shots were fired from a rifle with the first set grouping fine. It then opened up scatter gun style to 6" at 100 yds. Bore scoping the barrel revealed a seriously thermally eroded throat area and a small section of damaged rifling. This was picking up copper from the bullet jackets and causing fouling to build up to such an extent after a few rounds that unless cleaned every 3 shots, the rifle simply wouldn't group. New barrel job. Not suggesting this is the case here but if that is a consistent pattern of events, it's worth checking the bore. Seating depth changes of 4 thou will show up harmonics differences but at 6" in a random pattern, that's likely not a seating issue. I'd be checking action securing screws, scope and mounts and having a look at the bore.