Optimal Bullet Placement in Case?

Its alot more common on necked up stuff because you transition some of the shoulder to part of the neck.
I have never experienced it necking down
I made a 7x47 by necking up a 6.5x47. After firing a few rounds, I noticed a definite bump when I was seating a bullet. I wanted to turn the necks anyway, so I made a special effort on the neck-shoulder junction. It helped some, but not completely. Fortunately, I had a 6.5 neck reamer, and I ran that in with only light resistance until I came to the shoulder. Then, I cut a lot of brass from the inside of the neck.

About 40 years ago, I thought I would be smart and load some lead bullets in my 35 Whelen for some light recoiling target work. Because they were so much shorter then jacketed bullets, I only loaded them about half way down the neck. A few rounds in each case later, I noticed a donut "about half way down the neck." I took it to my gunsmith, and he said I had cut the neck of the chamber in the barrel. I had to have the barrel shortened, and the chamber recut.

I don't know if a full-house load will do that also, but if you seat your bullets shallow, and see a donut, you now know where it came from.
 
I'm all for keeping the bullet base out of the neck/shoulder junction. L.Sherm has it nailed in the donut issue and LanceKenyon is spot on with jump. Another consideration as it relates to neck, shoulder, donut concerns is the bullet itself. At the base of the bearing surface it frequently measures a bit larger than the rest of the bullet. Combine this with a donut and you have an inconsistent release.
 
It has been noted in most of my recorded data that the best seating depth runs .005"-.010" above where the heal meets the neck/shoulder juncture. It has never been below this.
I have had as little as 1/4 the calibre of the bullet in the neck without a single problem.

Cheers.
 
I've never had an issue with donuts on factory cartridges, this doesn't mean it cant or won't cause an issue.
I've got a couple wild cats that I 100% seat the bullet above the junction just to avoid any possible issues
 
I'm assuming we are talking about long range here. Under 600yds you can get away with a lot of stuff.
 
Really comes down to neck length of sizing rather than bearing seating depth.
If you size 1/2 the neck, deeper bearing than this should be clear of issues.
If you FL size necks?
I would not FL size necks no matter what.
 
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