Thread: Case neck sizing and effect on accuracy

How much of the case neck do you size?

On one hand, if full-length sizing using the die from a regular 2-piece set hard down onto the shell holder, a round using a case sized with this arrangement when chambered is presumably held in position at just the the two ends - by the case head on the bolt face, and the bullet shank in the freebore.

When the die is backed off the shell holder, or a bushing die is used, then there is the choice of how far down the neck to size. The unsized portion of the neck will remain at the fired diameter and help centre the top of the case, or at least that is the theory as I understand it. Depending on how much the case walls and shoulders have been taken back in, this may remain the only part of the case above the head that is a close fit to the chamber.

Then there is the question as to how much of the neck provides the ideal support for the bullet. Do long necks aid accuracy as is often proposed? If so then why have the bullet only supported by a fraction of the available neck? Maybe the advantage of long necks is to allow for both a section of neck left unsized for the above mentioned “centering” but with 4-5mm still left for the bullet? Maybe long necks aid accuracy only by a beneficial effect on throat erosion?

What is your thinking on this and why ?

Full length size everything. I am yet to see any kind of improvement in accuracy from messing about doing all sorts of silly little things that convinces me that time wouldn't be better spent behind a trigger, #1 factor that is going to affect accuracy is always the nut behind the bolt.

I tried this also and decided that the only reason to neck size is to save your brass, especially with a magnum. Maybe with a super accurate F-Class rifle it would make a difference?

Buggered if I know, you tell me.
My 6.5SAUM I neck size ( 2/3rd's of the neck) cleaned brass with a bushing die after turning the necks and trimming to uniform length. Anneal every time. Weigh each charge individually. Carefully seat the projectiles and check length etc. Gun shoots these into 1/2 to 1/4MOA depending on whether or not I am having a good day

Whereas I load range pickup 223 brass on my Dillon for my 6.5TCU including necking it up whilst de-priming at the first station. Powder measure fills the case at second station and bullet seated at the third. Shoots 1/4 to 1/2MOA Depending on whether or not I'm having a good day

my old .270 hates neck sized loads...they wont chamber properly or quickly,could be an off set chamber Im told so Ive always partial length resized as per instructions in my Nosler reloading manual. when doing 7.62x39mm rounds with .308 sized button in place it looks to resize about 3/4 of the neck and we have never yet had issues.
cant see point it totally full length resize unless your chamber is tight and needs it this way...like the plurry BLR does.... all you doing is working brass more than needed.

I have just started neck sizing for my 243 after full length for years. Taking careful measurements the difference between the bullet diameter and the neck sized is 2 thou. does the full length sized give more neck tension? I measured maybe 3 thou. Im using lee dies but felt the bullets could still be pushed further in by hand if I was rough with them after neck sized so I bought a lee crimper. From shooting at the range not much difference in group sizes between the 2 loads. Gun is a Remington SPS in 243. Need to start with new once fired brass and start again maybe the brass has gone hard in the neck and need annealing which I haven't had a go at yet. Any input or advice?

if it aint broke....dont try to fix it.
if you getting acceptable accuracy with FLR why change a good thing???
mabe try partial length resize eg back die out a turn not in a turn before setting locking ring
do 5 rounds identicle each way go fire the 15 and see what gives best result.....

I have yet to see anything ie data / tests to a reasonable scientific level that proves to my satisfaction that neck sizing is actually more accurate than full sizing. What I do see is the brass lasts a lot longer.

One thing I do think is important is neck tension so annealing the neck every few re-sizes, or any other work that makes the tension more consistent in this area seems to be worth the effort for competition work.

Hunting I think I'd always full resize to guarantee you can chamber a round when dinner turns up in front of you. As while target shooting I've had the odd occasion when I couldnt chamber a round, dinner would be long gone by the time a new round is ready to go.

Originally Posted by foxhound

I have just started neck sizing for my 243 after full length for years. Taking careful measurements the difference between the bullet diameter and the neck sized is 2 thou. does the full length sized give more neck tension? I measured maybe 3 thou. Im using lee dies but felt the bullets could still be pushed further in by hand if I was rough with them after neck sized so I bought a lee crimper. From shooting at the range not much difference in group sizes between the 2 loads. Gun is a Remington SPS in 243. Need to start with new once fired brass and start again maybe the brass has gone hard in the neck and need annealing which I haven't had a go at yet. Any input or advice?

Different dies will give slightly different sizes on the neck.
You don't need much tention at all. What you have is probably fine. But if you wish you can experiment. In saying that you can also change jump or powder weights to tune. it's probably easy to leave tention as is and experiment with other things first. If you have too much neck tention it can upset concentrcity.
You can polish expanderballs or lube inside the neck with graphite as well if your into experiments. It's a big old rabbit hole the reloading game. Simple is always good.

When you test full length sized cases and neck sized cases you might want to use a chronograph at the same time. You will likely find the neck sized cases will shoot a little faster but at least you will see which produces a more consistent velocity as well.

Originally Posted by Gillie

When you test full length sized cases and neck sized cases you might want to use a chronograph at the same time. You will likely find the neck sized cases will shoot a little faster but at least you will see which produces a more consistent velocity as well.

From what I've read and observed through my own loading it doesn't have much if any effect on sd. Consistency is key. Kinda doesnt matter which way you size, as long as it is consistent and concentric.

I used to neck size but now just partial fl size bumping the shoulder 2 thou or so. Worked well for me

For users of bushing dies, do you think that sizing just a small amount of the top of the neck can be used as a means reducing variation in the grip on the bullet brought about by the unavoidable spread in neck tension, and so have a beneficial effect on ES ?

Why would reducing the amount of neck holding the bullet have an adverse effect on concentricity, provided whatever sizing has been applied has been done so with minimal runout? Prior to ignition the unsized base of a fire-formed case neck is is snug fit with the chamber, the bullet shank is also sitting in the freebore - so there should be no difference in the way the bullet is presented to the leade prior to ignition. If reducing the length of neck holding the bullet does have an adverse effect on accuracy, it must be a dynamic thing, the effect being felt once the bullet is on the move. Perhaps having the neck sized for the entire length maintains the position of the base of the bullet for that little bit longer, or aids in a more even movement of the combustion gases around the base of the bullet at that critical moment, assisting the engraving in being marginally more symmetrical?

Originally Posted by Nick-D

From what I've read and observed through my own loading it doesn't have much if any effect on sd. Consistency is key. Kinda doesnt matter which way you size, as long as it is consistent and concentric.

Neck sizing only means the case should be pretty consistent with the chamber and reduces the amount you work the brass in the case. I would expect that over time and multiple reloads the case body and neck will work harden (unless you are also annealing) - the inconsistency in the body sizing versus brass properties should lead to velocity inconsistencies. Though I would expect this inconsistency to be slight.

In my limited testing (243Win and 260Rem, both Lapua cases and without annealing) neck sizing only resulted in slightly higher velocities and slightly more consistent velocities. For a hunting rifle or short distance rifle I wouldn't have seen the results in the groups - only on the chronograph. I saw better results at 500 yards with my 243 in terms of less vertical in the group (full length sized versus neck sized) and better results out to 1000m with the .260Rem with again less vertical.

Two rifles is hardly a comprehensive study though and I didn't prove my theory that repeated full length sizing without annealing would lead to more velocity inconsistency than repeated neck sizing.

My deal with neck sizing is that you get good consistency for a few firings then have to bump the shoulder anyway which gives you essentially a different load every few firings. Not a massive deal but still somthing you have to consider and adjust for.

I think most people over work their brass when fl sizing, you only have to bump the shoulder 2 thou or so. If you are full length sizing with this method then you are drastically minimising how much you work the brass.

For neck tension uniformity pretty much all the precision guys are annealing every load. Even with just neck sizing you as still too g to get some work hardening and a change in tension.

But at the end of the day it's all semantics and unless you are a br shooter or f class guy just use whatever system work for you. Carefull loading either way will make loads that shoot better than most rifles and shooters anyway.

I'm hunting not bench resting so prefer the so.plicity and reliability of partial fl sizing

Originally Posted by Nick-D

My deal with neck sizing is that you get good consistency for a few firings then have to bump the shoulder anyway which gives you essentially a different load every few firings. Not a massive deal but still somthing you have to consider and adjust for.

I tested this with my 260Rem - was here a measurably difference in velocity between cases I had just put through the bump die and those just fire formed. Yes, I found a very slight change in average velocity (lower on those just been through the bump die) - not enough for me to worry about in practical rifle competition out to and past 1000m.

Originally Posted by Nick-D

But at the end of the day it's all semantics and unless you are a br shooter or f class guy just use whatever system work for you. Carefull loading either way will make loads that shoot better than most rifles and shooters anyway.

I'm hunting not bench resting so prefer the simplicity and reliability of partial fl sizing

Absolutely agree with this approach. For my hunting rifle I neck size but as I have about 100 cases on the go and only need to bump about every 5 reloads it is going to take me a long time and a lot of hunting trips before I need to bump the shoulders on them.