Neck sizing and bumping the shoulder

[kcstott]

look for an Article written about the 7mm Practical It's a 300 WM necked to 7mm. the neat thing was this guy wrote a very nice article on how to properly chamber a Belted chamber to allow head spacing off the shoulder, Granted you are going to need to fireform your first batch of brass, but it was a neat idea,

[LynnJr]

Kwikvette
First thing that stands out is your brass is getting longer when fired? I notice nobody caught that?
Next never use an expander on your brass. If you need an expander ball your dies don't match your chamber.
Next subtract 0.003 from your loaded rounds outside diameter and use that bushing.
Doughnuts or donuts are formed when you stretch the case then try to shrink it back down moving the shoulder into the neck/shoulder junction of the brass.
The neck bushing doesn't size all the way to the neck/shoulder junction so it is actually larger not smaller.

[bsumoba]

Kwikvette
First thing that stands out is your brass is getting longer when fired? I notice nobody caught that?
Next never use an expander on your brass. If you need an expander ball your dies don't match your chamber.
Next subtract 0.003 from your loaded rounds outside diameter and use that bushing.
Doughnuts or donuts are formed when you stretch the case then try to shrink it back down moving the shoulder into the neck/shoulder junction of the brass.
The neck bushing doesn't size all the way to the neck/shoulder junction so it is actually larger not smaller

Lynn, I use an expander and a whole lot of people that I know are very good F-Class shooters use expanders/mandrels. The reason for us to use mandrels/expanders is because the necks are not necessarily consistent in thickness and if you are using a bushing die that sizes from the outside only, the neck I.D will ultimately be dependent on the neck thickness. So, for people who do not turn necks, bushing dies may result in a non-concentric neck I.D. The result is uneven neck tension and/or non-concentric loaded rounds.

Even if one were to turn necks, the fact that we have to trim means that the neck is stretching to some degree and IMO, that means the neck is thinning over time, which means even turned brass will change neck thickness as it is shot.

That being said, I have a custom FL sizing die (no bushing), where I defined my neck OD (because I do turn my necks) and my expander ball size to be such that when an expander ball runs up the neck, it just kisses the neck ID and expands it by about 0.001-0.0015". This is very minimal neck expanding, but it ensures that my neck ID is consistent and I have found my bullet seating pressure to be very consistent and my neck tension to be very consistent. Most non-bushing FL dies will size the neck down more than 0.004" under the finish size, which means that the expander ball sizes up the neck 0.004". One of the other advantages is my dies size all the way down to the neck/shoulder junction, which makes the neck/shoulder junction sharp and consistent. I agree with you that this is a potential issue when it comes to case life, thinning of necks, overworking brass, etc.

[LynnJr]

The typical dies you buy off the shelf oversize/overwork the brass at the neck and the shoulder area.
Expander buttons overwork the necks and in some examples they are actually 0.010+ in variation from swaging down to expanding back out.
Nothing is better than properly fitted dies to match your chamber but very few of them actually exist.
At 100 yards using a railguns you can actually see the affects of your necks on your groups.

[bsumoba]

The typical dies you buy off the shelf oversize/overwork the brass at the neck and the shoulder area.
Expander buttons overwork the necks and in some examples they are actually 0.010+ in variation from swaging down to expanding back out.
Nothing is better than properly fitted dies to match your chamber but very few of them actually exist.
At 100 yards using a railguns you can actually see the affects of your necks on your groups.

I agree with you. Custom dies are the only way to go and most will not go that route. My old 6.5 creedmoor FL die (off-the-shelf) actually does size it down close to 0.010" and I do not use it anymore.

My dies are now perfectly matched to my chamber.