Factory Case Neck is Slightly Smaller Than Lee Neck-Sized Case Neck

jaykchan · December 28, 2016, 07:42 PM

I have been using Lee neck sizing die for a while. It works OK, and I thought I had learnt how to use this die. But then I bought some factory new brass, and I find that the outside neck diameter of the new empty brass is slightly smaller than the outside neck diameter of my existing empty brass (that have been neck-sized using the Lee die).

The outside neck diameter of factory new 8mm empty brass is like 0.344".
The outside neck diameter of Lee neck sized 8mm empty brass is like 0.348".

Note: The factory new brass and my existing brass are all coming from the same manufacturer.

Is this a problem? As of now, the Lee neck sized cases seem to work fine. The brass can hold the bullet well, and I cannot use my finger to push in the bullet or to pull it out. I assume this means my Lee neck sizing die is setup OK. I straightly follow the Lee instruction to set it up (touch the shell holder and then turn in a full turn, and size each case twice with the case rotated between sizing). By the way I am using a Lee single stage Classic Cast Press.

I am asking this not only because the outside diameter of factory new case is slightly smaller than my Lee neck sized cases, but also has to do with the FPS of my handload seems not to be consistent. The extreme-spread of a 5-shots group can be from 60-fps to 160-fps. Something is not right. I am quite sure that the powder weight is correct because I weight each load twice using two different powder scales. I am wondering may be the neck tension is not consistent.

Should I use a 0.002' undersized mandrel to size my brass down to near the factory brass cases are? I have already owned the above-mentioned 0.002" undersized mandrel for 8mm die. Therefore, I could have tried it. But I really don't want to mess with the existing settings of my neck sizing die that I have carefully setup -- unless I know this is for a good reason.

Please let me know what you think. Thanks.

Jay Chan

jepp2 · December 28, 2016, 07:47 PM

Seat a bullet in each and measure again. That will tell you the neck tension you have and you can determine the neck wall thickness.

reddog81 · December 28, 2016, 09:29 PM

Is the brass from the same lot or box? It's possible if made at different times that different specs were used.

Are you using the same die to size and expand the neck. I'm no expert but I believe the expanding process is what sets the final diameter of the brass ( that is until the bullet is seated).

JeepHammer · December 28, 2016, 10:07 PM

To be quite frank about it,
Now you are ready for a sizing die with bushings for the size you are looking for.
99.99% of 'Reloaders' wouldn't measure, wouldn't know the difference, and wouldn't care.

Most simply 'Assume' the "One Size Fits All" (one size fits nothing) dies were 'Factory' and never even consider checking or correcting.

jaykchan · December 29, 2016, 09:15 PM

I re-measure the brase cases and I find that the neck size is a bit smaller than what I found yesterday. Last time I probably measured too close to the mouth where it might have expanded out slightly. I measured again. This time I stay 2mm to 3mm below the month. The difference is not as big (-0.004") as what I found yesterday. But the difference is still there (-0.002").

I have also followed jepp2's suggestion and seat bullets in several new brass cases. And measure the outside diameter of neck size with the bullets. I also measure the loaded rounds from existing twice-used brass cases, and factory new loaded rounds. The result is the following:

Factory new case: 0.348" w bullet, 0.3435" w/o bullet
Twice used case.: 0.347" w bullet, 0.3455" w/o bullet
Factory new ammo: 0.347" w bullet, N/A w/o bullet

You can see from above that the new measurement still finds that the factory new brass is still 0.002" slightly smaller than my twice-used brass.

You can also see that the outside diameter of factory new brass with bullet seated on it is actually 0.001" larger than that's of the twice-used brass with bullet. I thought the result would be the other way around. But the result is oppositive to what I thought.

I don't know why. May be someone can explain this to me?

Strangely the same is also true for factory new ammo. I assume the neck thickness of factory new brass "should" be the same as that's of the factory new ammo (they are from the same manufacturer). Then the outside neck diameter of both factory rounds with bullet should be the same, right? But they are not. May be the factory new ammo have been crimped, and my handloaded rounds are definitely not crimped.

Because the neck of factory new brass happens to be 0.002" smaller than my twice-used brass, I am really tempted to start using the 0.002" undersized mandrel to size the neck (to match the neck size of factory new brass), and start shooting some test groups to see what will happen. Moreover, I feel that there is _noticeably_ more tension to seat a bullet in the factory new brass than to seat a bullet in a twice-used brass. This is kind of appealing to me. Seem like smaller neck size can result with tighter neck tension. But I want to hear from forum members' opinion before I start trying many different things.

To answer reddog81's question: No, the brass cases are not from the same lot. This may cause the neck thickness to be different? I use the LEE neck sizing die to size the neck only (not full length size). I am not aware that it can expand the neck to receive a bullet. I have been using boat-tail bullets. Therefore, I cannot tell if the case mouth has been expanded or not. I run a finger over the case mouth, and I cannot tell if it is expanded or not either. Can lot-to-lot variation result with 0.002" difference? Please let me know. Thanks.

To JeepHammer: I don't think I am qualified to say anything about whether using sizing die with bushings will help or not. I am under the impression that experts in bench-rest shooting may be able to tell the difference. As for me, if my group size can be shrunk from 3.5" down to 2", I will be very happy. After-all, my rifle is a military surplus rifle from WWII, and it is still in its original full length military stock with front band and such. Therefore, I am not expecting too much. All I want are the FPS to be in a reasonable range and the group size down to 2". Having said this, I will keep what you said in mind when I need to work up a load for a sporterized mauser rifle.

Jay Chan

rootie3 · December 30, 2016, 07:01 PM

Your new brass came ready to reload... that is why the neck is smaller than your neck sizing die. As was mentioned above put a bullet in it and then measure...

Larry

jaykchan · December 31, 2016, 08:25 PM

Why the neck of factory new blank brass have to be smaller than used brass that have been neck-sized? Does this mean that mine have not been sufficiently sized down? I have followed LEE instruction to size my used brass in my LEE single stage press. But if this is not enough for some reason, please let me know. I am open to suggestion.

And I am not totally believe that LEE instruction is correct all the time either. For example, I used to use the same LEE neck sizing die to size my brass using a LEE Hand Press, and I followed the same instruction to setup the die. Unfortunately I found that the neck tension is VERY inconsistent. The neck tension of some cases (like 1 out of 20) were some light that I could use my fingers to pull the bullet in and out.

This problem is gone as soon as I replaced the LEE Hand Press with a LEE single stage press. This shows that I cannot totally believe in LEE instruction about how their die should be setup. This is the reason why I want to post a question here to hear what other people think about this issue (neck size of factory new brass is slightly smaller than the brass that I have neck-sized).

Yes, I have seat bullets in several factory new brass and I have posted the result in my last message posted yesterday.

Please let me know what you think. Thanks.

jaykchan · January 3, 2017, 05:31 PM

I read this article: http://www.accuracy-tech.com/neck-tension-hand-loaders/ about proper neck tension. And it said that I need to make sure the outside neck diameter of resized case (w/o bullet) should be 0.002" to 0.003" less than that's of a case that has a bullet seated in it; that is to maintain the proper neck tension. When I checked mine:

Factory new case: 0.348" w bullet, 0.3435" w/o bullet (-0.0045")
Twice used case.: 0.347" w bullet, 0.3455" w/o bullet (-0.0015")

This means my hand-load with twice-used cases are slightly not as tight as they should be. This explains the reason why I feel the tension doesn't seem to be tight enough when I seated a bullet on my twice-used cases. But it is not that much away from the desirable 0.002" neck tension. Therefore, this is probably OK.

As for the 0.0045" neck tension resulted from using the new factory brass, that is probably too much, and I should not use that neck size as the guide.

What this means is that I should not worry about the neck size of the new factory brass.

The article also said that this is desirable to have the neck tension a little bit high than (0.002" to 0.003") a little bid less (< 0.002"). This means the neck tension of my twice-used cases is probably a bit too loose. This "may" explain the reason why the FPS of my hand-load is not consistent. I will try several things to see which way will bring the neck tension of my hand-load to 0.002" to 0.003" range. Unfortunately I will need to wait for warmer days to test my hand-loads.

In other words, people here who asked me to seat a bullet to find out the result are all correct. I didn't know the significance of this advice until I have read that article.

Thanks for everyone who has taken the time to reply.

Jay Chan

**Unclenick** · January 3, 2017, 06:05 PM

First things first. It's the inside diameter of the case neck you are mainly interested in, not the outside. For the outside to be a valid indicator of the inside, you first need to confirm that the neck walls are the same thickness. Even in the same brands there can be variations. Due to sub-contracting brass out, even though the headstamp is the same, the brass isn't always made by the same factory on the same tooling. The SAAMI tolerance for the diameter of the brass over the bullet is minus 0.008", so there is some significant thickness range allowed.

If the necks are, indeed, the same wall thickness, then I would consider a tighter mandrel if you are not satisfied with how the cartridges shoot now. If you are satisfied with how they shoot now, don't narrow the mandrel, as that works the brass more and won't get as many reloads before the necks start to split or require annealing.

jaykchan · March 18, 2017, 10:57 AM

Sorry for getting back the result so late. Between waiting for items to be delivered and waiting for a warm weekend in the middle of a cold winter, I only managed to go to the shooting range one month ago to test my hand-loaded ammo.

I purchased the 0.002" undersized neck sizing mandrel from Lee, and used it to prepare ammo to see if the tighter neck tension may help me to get a consistent fps. Unfortunately the result was disappointing.

I didn't see any reduction of extreme-spread of fps. It surely didn't hurt. But it didn't help either. Therefore, I will have to look for a different avenue to improve my hand load. And that will be in a different message thread.

I will still continue using the undersized mandrel -- not for improving fps I use it for holding the bullet better to improve reliability (because I had a past experience of the neck tension was too loose and bullet in 1-of-20 case could be too loose).

I am posting the result just to let you know how this goes. Thanks for listening.

Longshot4 · March 18, 2017, 04:20 PM

I don't understand why you are concerned about your new brass neck size. But most of all I don't understand why you are neck sizing new brass. The brass comes all banged up... I would be Full Length sizing the brass and inspect the case length then measure it all again after it has been fire formed in your chamber. As your other brass has been. That is also a good time to inspect the length and trim if needed.

GripRigger · March 21, 2017, 07:36 PM

I don't know if I'm answering from the perspective you need but I just wanted to remind that the reason your factory cases are so much smaller is so the manufacturer can be sure their ammo will load/feed into any rifle including tighter target chambers.

And of course as you noted, when you fire form the brass it grows .......... it grows and then your sizer squeezes it smaller than it should be but the expander/sizing button coming back out gets it to the "correct" measurement. Unless you are using a Lee collet neck sizing die?

But as to your measuring.......are you using the exact same bullet make, type and weight as what is in the factory cartridge you are comparing it to? Have you measured, using a micrometer, the diameter of the new bullets against the factory bullets? I have measured between bullets in the same batch of 175gr SMK's and found differences in diameter as well as weight.

Perhaps you need to start over. Pull another factory bullet and measure it. Then sort through the bullets you use until you find one that is exactly the same dimensions and weight. And measure at 2-3 different points on the bullet seating area/shank/caliber diameter.

As mentioned before a lot has to do with the case neck thickness. If you have a proper thickness micrometer, you can measure it against the new brass.

I also am not sure if it's an accurate method to compare the necks of fired/sized brass against unfired new factory cartridges that you have pulled the bullet from. You got your sizer over-squeezing the neck of your fired brass and then the sizing button coming back through there opening it back up.....probably .002" difference to caliber size to allow for brass spring back. You don't really know what the neck tension/sizing process was during manufacture of the new factory cartridges. And as for factory new you are just pulling a bullet. There's no fire forming.

I also don't know if an inexpensive Lee neck die with an expander button is going to give you the exacting measurements you seem to need.

As mentioned already, consider going to a Redding Type-S or other bushing die. Or get a body die to bump the shoulder and a Lee collet die for the neck tension. These will give you more consistent neck tension. If you go this route you will also need to outside neck turn for the most consistent neck tension results.

I always FL size but that's just me. You would get your headspace and case body
sizing with the body die, which does not touch the neck......and then get the neck right with the bushing die. To me it sounds like this is what you need.

Not to bag on Lee but I will say that I have a 6.5 CM Lee FL sizing die that I swear is no good. It's not bumping the shoulder back enough and not sizing the lowermost portion of the brass enough. I have never been able to size with it as easily, comfortably and with an accurate shoulder bump as with my Redding and RCBS dies in .223, .308 and 7.65X53 Mauser. I have a Redding Type-S bushing die on order which in my heart I know will solve the sizing problems with the 6.5 Lee die.

Lastly.....shouldn't you be looking at factors like powder type and how accurate your powder drops are as far as the ES? Have you checked your scale(s).....calibrated etc etc? Do you sort and weigh cases and bullets and are you totally anal about powder weight? These things might have as much or more importance as far as ES, than neck tension alone.

I am sorry if I have missed the mark completely here and doubly sorry if I'm telling you things you know well already and didn't need my unsolicited ramblings.

I hope that at least something I said provided food for thought-if not for you but maybe someone else learning about this stuff. Unclenick is the guy to listen to along with Longshot and others.

December 28, 2016, 07:42 PM	#1
jaykchan Junior Member Join Date: April 7, 2013 Posts: 7	Factory Case Neck is Slightly Smaller Than Lee Neck-Sized Case Neck I have been using Lee neck sizing die for a while. It works OK, and I thought I had learnt how to use this die. But then I bought some factory new brass, and I find that the outside neck diameter of the new empty brass is slightly smaller than the outside neck diameter of my existing empty brass (that have been neck-sized using the Lee die). The outside neck diameter of factory new 8mm empty brass is like 0.344". The outside neck diameter of Lee neck sized 8mm empty brass is like 0.348". Note: The factory new brass and my existing brass are all coming from the same manufacturer. Is this a problem? As of now, the Lee neck sized cases seem to work fine. The brass can hold the bullet well, and I cannot use my finger to push in the bullet or to pull it out. I assume this means my Lee neck sizing die is setup OK. I straightly follow the Lee instruction to set it up (touch the shell holder and then turn in a full turn, and size each case twice with the case rotated between sizing). By the way I am using a Lee single stage Classic Cast Press. I am asking this not only because the outside diameter of factory new case is slightly smaller than my Lee neck sized cases, but also has to do with the FPS of my handload seems not to be consistent. The extreme-spread of a 5-shots group can be from 60-fps to 160-fps. Something is not right. I am quite sure that the powder weight is correct because I weight each load twice using two different powder scales. I am wondering may be the neck tension is not consistent. Should I use a 0.002' undersized mandrel to size my brass down to near the factory brass cases are? I have already owned the above-mentioned 0.002" undersized mandrel for 8mm die. Therefore, I could have tried it. But I really don't want to mess with the existing settings of my neck sizing die that I have carefully setup -- unless I know this is for a good reason. Please let me know what you think. Thanks. Jay Chan

December 28, 2016, 07:47 PM	#2
jepp2 Senior Member Join Date: December 24, 2008 Location: Loveland, CO Posts: 1,476	Seat a bullet in each and measure again. That will tell you the neck tension you have and you can determine the neck wall thickness. __________________ NRA Benefactor Life member

December 29, 2016, 09:15 PM	#5
jaykchan Junior Member Join Date: April 7, 2013 Posts: 7	Replies I re-measure the brase cases and I find that the neck size is a bit smaller than what I found yesterday. Last time I probably measured too close to the mouth where it might have expanded out slightly. I measured again. This time I stay 2mm to 3mm below the month. The difference is not as big (-0.004") as what I found yesterday. But the difference is still there (-0.002"). I have also followed jepp2's suggestion and seat bullets in several new brass cases. And measure the outside diameter of neck size with the bullets. I also measure the loaded rounds from existing twice-used brass cases, and factory new loaded rounds. The result is the following: Factory new case: 0.348" w bullet, 0.3435" w/o bullet Twice used case.: 0.347" w bullet, 0.3455" w/o bullet Factory new ammo: 0.347" w bullet, N/A w/o bullet You can see from above that the new measurement still finds that the factory new brass is still 0.002" slightly smaller than my twice-used brass. You can also see that the outside diameter of factory new brass with bullet seated on it is actually 0.001" larger than that's of the twice-used brass with bullet. I thought the result would be the other way around. But the result is oppositive to what I thought. I don't know why. May be someone can explain this to me? Strangely the same is also true for factory new ammo. I assume the neck thickness of factory new brass "should" be the same as that's of the factory new ammo (they are from the same manufacturer). Then the outside neck diameter of both factory rounds with bullet should be the same, right? But they are not. May be the factory new ammo have been crimped, and my handloaded rounds are definitely not crimped. Because the neck of factory new brass happens to be 0.002" smaller than my twice-used brass, I am really tempted to start using the 0.002" undersized mandrel to size the neck (to match the neck size of factory new brass), and start shooting some test groups to see what will happen. Moreover, I feel that there is _noticeably_ more tension to seat a bullet in the factory new brass than to seat a bullet in a twice-used brass. This is kind of appealing to me. Seem like smaller neck size can result with tighter neck tension. But I want to hear from forum members' opinion before I start trying many different things. To answer reddog81's question: No, the brass cases are not from the same lot. This may cause the neck thickness to be different? I use the LEE neck sizing die to size the neck only (not full length size). I am not aware that it can expand the neck to receive a bullet. I have been using boat-tail bullets. Therefore, I cannot tell if the case mouth has been expanded or not. I run a finger over the case mouth, and I cannot tell if it is expanded or not either. Can lot-to-lot variation result with 0.002" difference? Please let me know. Thanks. To JeepHammer: I don't think I am qualified to say anything about whether using sizing die with bushings will help or not. I am under the impression that experts in bench-rest shooting may be able to tell the difference. As for me, if my group size can be shrunk from 3.5" down to 2", I will be very happy. After-all, my rifle is a military surplus rifle from WWII, and it is still in its original full length military stock with front band and such. Therefore, I am not expecting too much. All I want are the FPS to be in a reasonable range and the group size down to 2". Having said this, I will keep what you said in mind when I need to work up a load for a sporterized mauser rifle. Jay Chan Last edited by jaykchan; December 30, 2016 at 08:06 AM.

December 30, 2016, 07:01 PM	#6
rootie3 Junior Member Join Date: December 14, 2011 Posts: 9	smaller neck Your new brass came ready to reload... that is why the neck is smaller than your neck sizing die. As was mentioned above put a bullet in it and then measure... Larry

December 31, 2016, 08:25 PM	#7
jaykchan Junior Member Join Date: April 7, 2013 Posts: 7	Why? Why the neck of factory new blank brass have to be smaller than used brass that have been neck-sized? Does this mean that mine have not been sufficiently sized down? I have followed LEE instruction to size my used brass in my LEE single stage press. But if this is not enough for some reason, please let me know. I am open to suggestion. And I am not totally believe that LEE instruction is correct all the time either. For example, I used to use the same LEE neck sizing die to size my brass using a LEE Hand Press, and I followed the same instruction to setup the die. Unfortunately I found that the neck tension is VERY inconsistent. The neck tension of some cases (like 1 out of 20) were some light that I could use my fingers to pull the bullet in and out. This problem is gone as soon as I replaced the LEE Hand Press with a LEE single stage press. This shows that I cannot totally believe in LEE instruction about how their die should be setup. This is the reason why I want to post a question here to hear what other people think about this issue (neck size of factory new brass is slightly smaller than the brass that I have neck-sized). Yes, I have seat bullets in several factory new brass and I have posted the result in my last message posted yesterday. Please let me know what you think. Thanks.

December 28, 2016, 09:29 PM	#3
reddog81 Senior Member Join Date: October 16, 2014 Location: Iowa Posts: 1,634	Is the brass from the same lot or box? It's possible if made at different times that different specs were used. Are you using the same die to size and expand the neck. I'm no expert but I believe the expanding process is what sets the final diameter of the brass ( that is until the bullet is seated).

December 28, 2016, 10:07 PM	#4
JeepHammer Junior member Join Date: February 27, 2015 Posts: 1,768	To be quite frank about it, Now you are ready for a sizing die with bushings for the size you are looking for. 99.99% of 'Reloaders' wouldn't measure, wouldn't know the difference, and wouldn't care. Most simply 'Assume' the "One Size Fits All" (one size fits nothing) dies were 'Factory' and never even consider checking or correcting.

January 3, 2017, 05:31 PM	#8
jaykchan Junior Member Join Date: April 7, 2013 Posts: 7	Should be Nothing Wrong I read this article: http://www.accuracy-tech.com/neck-tension-hand-loaders/ about proper neck tension. And it said that I need to make sure the outside neck diameter of resized case (w/o bullet) should be 0.002" to 0.003" less than that's of a case that has a bullet seated in it; that is to maintain the proper neck tension. When I checked mine: Factory new case: 0.348" w bullet, 0.3435" w/o bullet (-0.0045") Twice used case.: 0.347" w bullet, 0.3455" w/o bullet (-0.0015") This means my hand-load with twice-used cases are slightly not as tight as they should be. This explains the reason why I feel the tension doesn't seem to be tight enough when I seated a bullet on my twice-used cases. But it is not that much away from the desirable 0.002" neck tension. Therefore, this is probably OK. As for the 0.0045" neck tension resulted from using the new factory brass, that is probably too much, and I should not use that neck size as the guide. What this means is that I should not worry about the neck size of the new factory brass. The article also said that this is desirable to have the neck tension a little bit high than (0.002" to 0.003") a little bid less (< 0.002"). This means the neck tension of my twice-used cases is probably a bit too loose. This "may" explain the reason why the FPS of my hand-load is not consistent. I will try several things to see which way will bring the neck tension of my hand-load to 0.002" to 0.003" range. Unfortunately I will need to wait for warmer days to test my hand-loads. In other words, people here who asked me to seat a bullet to find out the result are all correct. I didn't know the significance of this advice until I have read that article. Thanks for everyone who has taken the time to reply. Jay Chan

January 3, 2017, 06:05 PM	#9
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,061	First things first. It's the inside diameter of the case neck you are mainly interested in, not the outside. For the outside to be a valid indicator of the inside, you first need to confirm that the neck walls are the same thickness. Even in the same brands there can be variations. Due to sub-contracting brass out, even though the headstamp is the same, the brass isn't always made by the same factory on the same tooling. The SAAMI tolerance for the diameter of the brass over the bullet is minus 0.008", so there is some significant thickness range allowed. If the necks are, indeed, the same wall thickness, then I would consider a tighter mandrel if you are not satisfied with how the cartridges shoot now. If you are satisfied with how they shoot now, don't narrow the mandrel, as that works the brass more and won't get as many reloads before the necks start to split or require annealing. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

March 18, 2017, 10:57 AM	#10
jaykchan Junior Member Join Date: April 7, 2013 Posts: 7	Undersized Mandrel Doesn't Help in FPS Consistence Sorry for getting back the result so late. Between waiting for items to be delivered and waiting for a warm weekend in the middle of a cold winter, I only managed to go to the shooting range one month ago to test my hand-loaded ammo. I purchased the 0.002" undersized neck sizing mandrel from Lee, and used it to prepare ammo to see if the tighter neck tension may help me to get a consistent fps. Unfortunately the result was disappointing. I didn't see any reduction of extreme-spread of fps. It surely didn't hurt. But it didn't help either. Therefore, I will have to look for a different avenue to improve my hand load. And that will be in a different message thread. I will still continue using the undersized mandrel -- not for improving fps I use it for holding the bullet better to improve reliability (because I had a past experience of the neck tension was too loose and bullet in 1-of-20 case could be too loose). I am posting the result just to let you know how this goes. Thanks for listening.

March 18, 2017, 04:20 PM	#11
Longshot4 Senior Member Join Date: February 22, 2014 Posts: 868	I don't understand why you are concerned about your new brass neck size. But most of all I don't understand why you are neck sizing new brass. The brass comes all banged up... I would be Full Length sizing the brass and inspect the case length then measure it all again after it has been fire formed in your chamber. As your other brass has been. That is also a good time to inspect the length and trim if needed.

March 21, 2017, 07:36 PM	#12
GripRigger Junior Member Join Date: March 18, 2017 Location: Los Angeles Posts: 11	I don't know if I'm answering from the perspective you need but I just wanted to remind that the reason your factory cases are so much smaller is so the manufacturer can be sure their ammo will load/feed into any rifle including tighter target chambers. And of course as you noted, when you fire form the brass it grows .......... it grows and then your sizer squeezes it smaller than it should be but the expander/sizing button coming back out gets it to the "correct" measurement. Unless you are using a Lee collet neck sizing die? But as to your measuring.......are you using the exact same bullet make, type and weight as what is in the factory cartridge you are comparing it to? Have you measured, using a micrometer, the diameter of the new bullets against the factory bullets? I have measured between bullets in the same batch of 175gr SMK's and found differences in diameter as well as weight. Perhaps you need to start over. Pull another factory bullet and measure it. Then sort through the bullets you use until you find one that is exactly the same dimensions and weight. And measure at 2-3 different points on the bullet seating area/shank/caliber diameter. As mentioned before a lot has to do with the case neck thickness. If you have a proper thickness micrometer, you can measure it against the new brass. I also am not sure if it's an accurate method to compare the necks of fired/sized brass against unfired new factory cartridges that you have pulled the bullet from. You got your sizer over-squeezing the neck of your fired brass and then the sizing button coming back through there opening it back up.....probably .002" difference to caliber size to allow for brass spring back. You don't really know what the neck tension/sizing process was during manufacture of the new factory cartridges. And as for factory new you are just pulling a bullet. There's no fire forming. I also don't know if an inexpensive Lee neck die with an expander button is going to give you the exacting measurements you seem to need. As mentioned already, consider going to a Redding Type-S or other bushing die. Or get a body die to bump the shoulder and a Lee collet die for the neck tension. These will give you more consistent neck tension. If you go this route you will also need to outside neck turn for the most consistent neck tension results. I always FL size but that's just me. You would get your headspace and case body sizing with the body die, which does not touch the neck......and then get the neck right with the bushing die. To me it sounds like this is what you need. Not to bag on Lee but I will say that I have a 6.5 CM Lee FL sizing die that I swear is no good. It's not bumping the shoulder back enough and not sizing the lowermost portion of the brass enough. I have never been able to size with it as easily, comfortably and with an accurate shoulder bump as with my Redding and RCBS dies in .223, .308 and 7.65X53 Mauser. I have a Redding Type-S bushing die on order which in my heart I know will solve the sizing problems with the 6.5 Lee die. Lastly.....shouldn't you be looking at factors like powder type and how accurate your powder drops are as far as the ES? Have you checked your scale(s).....calibrated etc etc? Do you sort and weigh cases and bullets and are you totally anal about powder weight? These things might have as much or more importance as far as ES, than neck tension alone. I am sorry if I have missed the mark completely here and doubly sorry if I'm telling you things you know well already and didn't need my unsolicited ramblings. I hope that at least something I said provided food for thought-if not for you but maybe someone else learning about this stuff. Unclenick is the guy to listen to along with Longshot and others.