6.5 CM Neck Tension Question

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I have been reloading for about 10 years now, but just recently got my first set of bushing dies (Hornady Match) to reload for my 6.5CM.

I purchased new Lapua brass and simply lubed and ran it through the sizing die for case prep. I used the sizing die with a 0.290” bushing and removed the expander stem.

I loaded 50 rounds with this brass (140 accubonds and h4350) and worked up the load trying to find pressure.

At 42 grains of powder I was getting approximately 2850 fps.

I wanted to do my actual load development with 1x fired brass. So I cleaned, lubed and sized the brass with the same 0.290 bushing (die was set to bump shoulder ~.001”). I also used my Lee trimmer to trim the brass to 1.905” (Virgin brass was 1.912”).

During bullet seating I noticed there was not much resistance. Upon inspection, I could move the bullet into the case without much effort. I proceeded anyway and loaded another 40 rounds of the once fired brass and shot additional groups.

Although I didn’t shoot as broad of range of powder charges, my velocity was approximately 150-FPS lower with the 1x brass than with the virgin brass.

I did some measurements and came up with the following:
1x Brass:
Case Neck OD (empty) - 0.2895”
Case Neck OD (after loading) - 0.2910”
Neck Tension - 0.0015”
Length - 1.905”
Bullet can be moved in case

Virgin Brass:
Case Neck OD (empty) - 0.2895”
Case Neck OD (after loading) - 0.2905”
Neck Tension - 0.0010”
Length - 1.912”
Bullet is firmly held in case.

My thought is to order a 0.288” bushing to increase the neck tension and provide a firmer hold on the bullet. I am a bit stumped as to why the virgin brass is firmly holding the bullet with less neck tension though.

Am I missing a step thats creating this issue? Any thoughts on why I’m seeing such a large velocity change?
 

918v

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You’re measuring wrong. This is probably because you’re using a caliper that is inaccurate. .0015” neck tension will hold the bullet well enough that it cannot be moved.

And yes, if the bullet slides in and out then the velocity will suffer due to poor combustion.
 

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You’re measuring wrong. This is probably because you’re using a caliper that is inaccurate. .0015” neck tension will hold the bullet well enough that it cannot be moved.

And yes, if the bullet slides in and out then the velocity will suffer due to poor combustion.

Thank you for the feedback. As you noted, I am using calipers that may be inaccurate or not be capable of the level of precision im after.

Given that the OD of 50 pieces of brass measured exactly 0.2895” after sizing in a 0.290” bushing and the bullets themselves measured 0.264” I had figured I was getting accurate readings.

Seems logical that moving to a 0.288” bushing would provide proper neck tension so I will go that route.
 
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rady

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Curious as to what you are using for calipers? Electronic out to 0.0001"? Accuracy of those is usually only about +- 0.001".
Lapua brass tends to run thicker, so what you are describing is a bit unusual.
 
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he lives

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Curious as to what you are using for calipers? Electronic out to 0.0001"? Accuracy of those is usually only about +- 0.001".
Lapua brass tends to run thicker, so what you are describing is a bit unusual.

Yes digital calipers that read out to 0.00001". I was using the 0.290" bushing because I was expecting the lapua brass to run thicker as well.

I went back and remeasured some of the once fired and virgin brass with a micrometer to get a second set of readings. Based on those measurements, it appears that the virgin brass has 0.002" neck tension, where the once fired has 0.001" of neck tension. These readings are in better agreement with the loose bullets and reduced velocity.

I am planning to order a 0.288" and 0.286" bushing to provide 0.002" to 0.003" of neck tension on the once fired brass.

I appreciate the insight.

On a separate note, do most use the bushing dies without the expander stem installed?
 

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On a separate note, do most use the bushing dies without the expander stem installed?
I leave the post and decapping pin installed but remove/swap out the expander ball in my Redding’s. I dont have other bushing dies to speak to specifics on.
For my honed neck dies I gut them entirely.

EditL I lied, I do have one redding bushing die that I took the whole post out of. It doesnt really matter so long as you make sure that everything you need gets done to the brass one way or another.
 
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Yes digital calipers that read out to 0.00001". I was using the 0.290" bushing because I was expecting the lapua brass to run thicker as well.

I went back and remeasured some of the once fired and virgin brass with a micrometer to get a second set of readings. Based on those measurements, it appears that the virgin brass has 0.002" neck tension, where the once fired has 0.001" of neck tension. These readings are in better agreement with the loose bullets and reduced velocity.

I am planning to order a 0.288" and 0.286" bushing to provide 0.002" to 0.003" of neck tension on the once fired brass.

I appreciate the insight.

On a separate note, do most use the bushing dies without the expander stem installed?

.001” neck tension would not produce loose bullets. Only zero neck tension produces loose bullets.

Get yourself a certified dial caliper, either a Starrett ($250) or Mitutoyo ($150) that is accurate and when it says .290” it’s .290” and not .289” or .291”. That is the easiest way to play with .001” dimensional increments. Or plug gauges but a good caliper is more versatile.

I have a Forster sizing die with the neck honed to .288”. You’re going to need an expander mandrel still.
 

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If you removed the whole decapping rod/button sizing mandrel, & forgot to throw the black lock nut that secures the decapping rod to the stem back into the top of the stem, so it could serve as a space occupier, whereby it sits on top of the bushing, you may’ve gotten only a fraction of the neck resized by the bushing. If that lock nut isn’t there, there’s nothing to prevent the bushing inside the stem from raising up, even if the stem was tightened all the way down. That could potentially account for the loose bullet fit.
1623811285238.jpeg
 
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rady

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If you removed the whole decapping rod/button sizing mandrel, & forgot to throw the black lock nut that secures the decapping rod to the stem back into the top of the stem, so it could serve as a space occupier, whereby it sits on top of the bushing, you may’ve gotten only a fraction of the neck resized by the bushing. If that lock nut isn’t there, there’s nothing to prevent the bushing inside the stem from raising up, even if the stem was tightened all the way down. That could potentially account for the loose bullet fit. View attachment 7648182
This may explain what you are seeing. I've also read where the top locking ring and knurled spindle body can allow a small amount (1/4 to1/2 turn) of bushing float in redding s type dies. Not sure how your Hornady dies are set up. If there isn't a lock nut for your spindle, then you may be able to adjust the spindle to allow for the bushing to achieve close to full neck sizing. It could be something as simple as adjusting that spindle down. Worth trying as opposed to buying additional bushings.
 
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he lives

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Sounds like the hornady dies are set up a little different than the dies you are referencing.

I was unclear in my previous posts. I am using the dies with the decap pin retainer (part 12 in image below) instead if the expander (part 13 in image below).

I went ahead and ordered 0.286" and 0.288" bushings and plan to get certified dial calipers. I'll know more after measuring, but thinking I may run the brass through the dies twice. Once with the 0.290" bushing and expander, then again with the smaller bushing and no expander.




Screenshot 2021-06-16 070844.png
 

RldrNewby

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Sounds like the hornady dies are set up a little different than the dies you are referencing.

I was unclear in my previous posts. I am using the dies with the decap pin retainer (part 12 in image below) instead if the expander (part 13 in image below).

I went ahead and ordered 0.286" and 0.288" bushings and plan to get certified dial calipers. I'll know more after measuring, but thinking I may run the brass through the dies twice. Once with the 0.290" bushing and expander, then again with the smaller bushing and no expander.




View attachment 7648367
I went back & read your initial post, & realized I had looked right over where you stated it was Hornady Match Bushing Die. I haven’t used those yet, and my only experience has been with Redding Type-S Bushing Dies, so my apologies if my post was misleading. Thanks for sharing the Parts list pic. At least I have a better understanding of how Hornady’s Bushing Dies are constructed now. Good luck to u sir!
 

WilburW

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For comparison, I use a .289 neck bushing for my Lapua 6.5CM brass. This is in a Redding Type S, but the bushing size is relevant. I removed the expander ball, and instead use the Sinclair expander mandrel. Although rated for .001 next tension, actual neck tension result is more like .0015, likely due to brass "spring-back."

Projectiles are well seated. Results are excellent. Consistent single-digit SD's.
 

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For comparison, I use a .289 neck bushing for my Lapua 6.5CM brass. This is in a Redding Type S, but the bushing size is relevant. I removed the expander ball, and instead use the Sinclair expander mandrel. Although rated for .001 next tension, actual neck tension result is more like .0015, likely due to brass "spring-back."

Projectiles are well seated. Results are excellent. Consistent single-digit SD's.
That's good info and would explain why my 0.290" bushing is giving very little neck tension.
 

WilburW

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That's good info and would explain why my 0.290" bushing is giving very little neck tension.
Just thinking .286 might be way too tight for the thicker Lapua brass.
Even with .288, you might end up shaving off bits of copper during bullet seating. If so, try .289....
 
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918v

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Just thinking .286 might be way too tight for the thicker Lapua brass.
Even with .288, you might end up shaving off bits of copper during bullet seating. If so, try .289....
A properly prepared neck won’t shave bullet jackets.
 
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Graye2

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With Lapua brass I use a .289 bushing and then a 21st century .002 expander checking with pin gauges I get consistent .0015 neck tension which works well for me...you can’t move it by hand. I use a Redding micrometer die and I only size the neck about 50% of the way down to allow for better chambering of the brass (if you buy the new SAC dies they are already set up this way).

Are you planning to use a mandrel after your bushing die? If not with a .288 or .286 I think you’ll get a lot more neck tension given my Lapua Brass is fairly consistent neck thickness of 0.0135 to 0.0140 from various boxes measured with a dial micrometer. With that neck thickness you are around .291 to .292 and will end up with neck tension well over .002 (annealing, spring back, etc will all cause variation).

I would buy a few pin gauges and see where you are before investing in a smaller bushing. They are $4 a piece and will give you a better measurement than calipers. If could be that you have a larger chamber and with spring back your not getting a full .290 size. I’d be curious to know what’s the neck size of a fired round before resizing?
 

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With Lapua brass I use a .289 bushing and then a 21st century .002 expander checking with pin gauges I get consistent .0015 neck tension which works well for me...you can’t move it by hand. I use a Redding micrometer die and I only size the neck about 50% of the way down to allow for better chambering of the brass (if you buy the new SAC dies they are already set up this way).

Are you planning to use a mandrel after your bushing die? If not with a .288 or .286 I think you’ll get a lot more neck tension given my Lapua Brass is fairly consistent neck thickness of 0.0135 to 0.0140 from various boxes measured with a dial micrometer. With that neck thickness you are around .291 to .292 and will end up with neck tension well over .002 (annealing, spring back, etc will all cause variation).

I would buy a few pin gauges and see where you are before investing in a smaller bushing. They are $4 a piece and will give you a better measurement than calipers. If could be that you have a larger chamber and with spring back your not getting a full .290 size. I’d be curious to know what’s the neck size of a fired round before resizing?

Graye2 -

I already purchased the 0.286" and 0.288" bushings (should be here monday) so that I would have a couple options to play with if needed. I also have a set of certified calipers being delivered tomorrow.

With the sinclair mandrel die out of stock and the 21st century die showing a 4 week lead time, my plan for the short term is to measure the expander on the die I have and see where its at.

Are you saying you use an expander die that measure 0.262" and end up with 0.0015" neck tension after expanding? For the pin gauges, what sizes would you recommend ordering?
 

Graye2

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Yes, with a 0.262 expander mandrel I land at .0015. I do anneal after every firing.

For .264 I bought pins from 0.261 to .264 in .00005 increments...all minus gauges.
 
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Halfnutz

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    .261 through .264 will get you there.
    Pin gages come in -(minus) and +(plus) tolerances. For inside diameters you want minus.
     

    he lives

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    With Lapua brass I use a .289 bushing and then a 21st century .002 expander checking with pin gauges I get consistent .0015 neck tension which works well for me...you can’t move it by hand. I use a Redding micrometer die and I only size the neck about 50% of the way down to allow for better chambering of the brass (if you buy the new SAC dies they are already set up this way).

    Are you planning to use a mandrel after your bushing die? If not with a .288 or .286 I think you’ll get a lot more neck tension given my Lapua Brass is fairly consistent neck thickness of 0.0135 to 0.0140 from various boxes measured with a dial micrometer. With that neck thickness you are around .291 to .292 and will end up with neck tension well over .002 (annealing, spring back, etc will all cause variation).

    I would buy a few pin gauges and see where you are before investing in a smaller bushing. They are $4 a piece and will give you a better measurement than calipers. If could be that you have a larger chamber and with spring back your not getting a full .290 size. I’d be curious to know what’s the neck size of a fired round before resizing?

    Haven’t had a chance to order pin gauges, but did get a set of certified calipers.

    Using the new calipers the fired brass measures 0.295” to 0.296” before sizing.

    Updated readings using the new calipers:

    1x Brass:
    Case Neck OD (empty) - 0.290”
    Case Neck OD (after loading) - 0.2905”

    Virgin Brass:
    Case Neck OD (empty) - 0.2895”
    Case Neck OD (after loading) - 0.292”

    Those measurements are based on one casing each, not an average of multiple cases.

    Looks like moving down to a 0.288” bushing may replicate the neck tension I was getting with the virgin brass.
     
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    Graye2

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    Ok...for reference I measured 10 fired cases and all were .296. I also measured 10 loaded rounds and all measured .291. All of these were checked with pin gauges before loading and were 0.2625.
     

    ReaperDriver

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    Curious as to what you are using for calipers? Electronic out to 0.0001"? Accuracy of those is usually only about +- 0.001".
    Lapua brass tends to run thicker, so what you are describing is a bit unusual.
    Agree. My Lapua loaded OD dimensions typically run in the .2935 range and and I run a .292 bushing for the bolt gun and a .291 for the gas gun. There is plenty of neck tension there. I'm using a Mitutoyo digital caliper.
     

    918v

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    Are you guys measuring using the thin part or the thick part of the jaws?
     

    JimGnitecki

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    Yes digital calipers that read out to 0.00001". I was using the 0.290" bushing because I was expecting the lapua brass to run thicker as well.

    I went back and remeasured some of the once fired and virgin brass with a micrometer to get a second set of readings. Based on those measurements, it appears that the virgin brass has 0.002" neck tension, where the once fired has 0.001" of neck tension. These readings are in better agreement with the loose bullets and reduced velocity.

    I am planning to order a 0.288" and 0.286" bushing to provide 0.002" to 0.003" of neck tension on the once fired brass.

    I appreciate the insight.

    On a separate note, do most use the bushing dies without the expander stem installed?
    Only digital MICROMETERS show 5 decimal places. There is no digital CALIPER that shows 5 decimal places. They show 4 decimals only, AND that 5th decimal can only read either a "0" or a "5". But even that is deceptive, because as someone else has already pointed out, the inherent accuracy of even the veyr best (Mitutoyo, Starret) calipers is .001" at best, IF YOU apply consistent pressure to the device AND have the itrem being measured precisely square, AND check periodically between items to ensure that with the jaws closed you have a "0.0000" reading, and not 0.0005 or -0.0005.

    I load my Lapua brass - wall thickness .0145"- using the nitrate .291" bushing and Hornady 120g bullets that measure as .2636". This predicts that neck tension will be .291" minus (.0145" x 2) minus .2636" = .0016" neck tension. And, indeed, my Mitutoyo caliper consistent says that a previously fired case does come out of the sizing die at .290", and the actual neck tension is good, and the rifle shoots nice tight groups.

    So, I think you might have a measurement problem that is caused by a combination of the caliper limitations or its condition, and operator inconsistency on pressure and/or placement of the item being measured.

    By the way, I do have the expander in the Redding Type S neck sizing die, and it does NOT result in "undoing" the .290" OD created by the bushing. On GOOD brass (like the Lapua), the expander does NOT make the OD larger UNLESS that is required in order to correct a too small neck ID and / or non-concentric neck ID, created by inconsistent non-concentric neck wall thickness. Sure, in this case, yes, the .290" OD would be violated, bu that's better than a too small ID or non-concentric ID.

    Jim G
     
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    JimGnitecki

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    Are you guys measuring using the thin part or the thick part of the jaws?
    Depends on WHAT you are measuring. For most items being measured, you use the wide part, which on the best calipers, is also a special harder material than the rest of the jaw. But for items that are both curved and concave, you must use the thinner part of the jaws in order to avoid "bridging" across the concave surface (e.g. when measuring wall thickness with the caliper because you don't own a ball micrometer.) But that narrow part exerts more "psi" on the item because it is a smaller surface area of contact, and the narrow part is also easy to deform if not made of the hardened material, or can deform the item being measured if it IS the hardened material. So if you push too hard, you can deform both the item being measured and the caliper jaw. You need some sensitivity and skill to do caliper measurements correctly.

    Jim G
     
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    rady

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    I’m measuring at the very top of the neck using Mitutoyo certified dial calipers.
    I believe that is a problem. From all that I have read and videos viewed, it is best to use the thicker portion of the jaws and DON'T measure at the top.
    Are you guys measuring using the thin part or the thick part of the jaws?
    Thick.
     

    Graye2

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    I just checked the same 10 rounds with my mitutoyo’s...thin portion of caliper is consistent at .291 (pretty much any where on the sized portion of my necks). I only size the top 50% of my necks with my micrometer neck sizer so with the thick portion of the calipers I’m .292 but I’m running close to the unsized portion of the neck at that point.
     
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    918v

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    The reason I asked is depending on how you measure you’ll get a different reading and this explains the discrepancy between two people measuring the same thing.

    If you measure the neck in the middle using the thick part of the jaws they will catch the lower part of the neck where the sizing bushing left a radius and the reading wI’ll be bigger.

    For the sake of this discussion it would be nice if everyone measured the same way so the numbers made sense. As it is right now the numbers are all over the place and it’s not because the brass varies that much.
     
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    rustyinbend

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    I use a Redding Type-S Bushing Die to size-down (decapping pin/expander ball removed), and then a 21st Century Expander Mandrel to size back up to the proper neck tension. The .2645 mandrel is giving me solid results in 6.5-CM. Oh ... and I anneal after every firing to ensure good brass elasticity.
     

    Baron23

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    The .2645 mandrel is giving me solid results in 6.5-CM.
    I'm guessing that using .2645 mandrel for a .264 bullet works because of spring back?

    Have you used pin gages or the like to confirm degree of spring back and ID or you just happy that this combo is shooting very well.

    Not trying to put you on the spot....just trying to learn a bit about bushing dies and mandrels as right now I just use a Redding FL die with expander ball.
     

    WilburW

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    OP: The Sinclair Expander mandrel for 6.5/.264 measures .263”, for an intended .001“ neck tension.

    In reality, because the brass doesn’t hold that diameter, it “springs back” about a half of a thousandth. I end up with about .0015” (I.e. one and one-half thousands) of neck tension…
     

    Snuby642

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    I run fls with expanders sanded to yield - 0.004 on average.

    Then everything gets the Sinclair mandrell - 0.002 treatment.

    As long as you don't have a neck turn chamber situation every piece of brass is consistant.

    That dropped group size accross the calibers.

    No bushings, no measurements no bullshit ever again.

    You can get mesurement tools calibrated in a lab (wtf is certified anyway) but it needs recalibrated constantly.

    Why in hell would you stress over that little sticker when you can buy a piece of precision ground tool steal once and check your own tools forever.

    Measuring neck tension is in the past, different bushings etc also in the past and any 30 cal varient cartridge is covered by the one 30 cal mandrell .

    Quit wasting time on that crap.

    I satisfied my criteria by doing this on least count 6 different head stamps. They all started grouping better and much closer to the same.

    The slight case volumetric difference in cases was way less noticable at all and determined that neck tension rules the day.

    Imho
     
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    918v

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    I'm guessing that using .2645 mandrel for a .264 bullet works because of spring back?

    Have you used pin gages or the like to confirm degree of spring back and ID or you just happy that this combo is shooting very well.

    Not trying to put you on the spot....just trying to learn a bit about bushing dies and mandrels as right now I just use a Redding FL die with expander ball.

    I think he misspoke. If you run a .2645” mandrel through a 6.5 neck you will not have enough grip on the bullet. I don’t think anyone makes a .2645” mandrel. The biggest expander I am aware of is RCBS (meant for oversized lead projectiles) which mics .2640”
     

    rady

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    I think he misspoke. If you run a .2645” mandrel through a 6.5 neck you will not have enough grip on the bullet. I don’t think anyone makes a .2645” mandrel. The biggest expander I am aware of is RCBS (meant for oversized lead projectiles) which mics .2640”
    21st does. If you buy one of their Sets you get the following:

    "Our caliber specific expander mandrels are available in .0005” increments in calibers 22 to 338 and will range from .001” above bullet diameter to at least .003” below bullet diameter depending on caliber."

    But they also make a 0.2645 mandrel, if you so desire, and many other in-between mandrels. I can see why so many like the 21st stuff.

    The reason I asked is depending on how you measure you’ll get a different reading and this explains the discrepancy between two people measuring the same thing.

    If you measure the neck in the middle using the thick part of the jaws they will catch the lower part of the neck where the sizing bushing left a radius and the reading wI’ll be bigger.

    For the sake of this discussion it would be nice if everyone measured the same way so the numbers made sense. As it is right now the numbers are all over the place and it’s not because the brass varies that much.
    I've never had a problem with hitting the unsized portion of the neck with the thicker portion of the jaws.
     

    Brettmparker1

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    I bounce between .288/.289 i do have the .290 but I ran into similar problems. If you can move the bullet in and out by hand with little effort there is not enough neck tension. But like all the witchcraft involved in reloading what works for some does not for others.
     

    JimGnitecki

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    I bounce between .288/.289 i do have the .290 but I ran into similar problems. If you can move the bullet in and out by hand with little effort there is not enough neck tension. But like all the witchcraft involved in reloading what works for some does not for others.

    Yes, I guess there is some witchcraft, because I use the Redding .291" sizing bushing, and as the math I showed a few posts earlier shows (.291" minus (.0145"x2 wall thickness) - .2636" Hornady bullet OD), it makes for a "perfect" .0016" neck tension.

    And that .0016" neck tension is sufficient that when I screw up on BTO and make the cartridge too short, it takes MANY wacks with the inertia kinetic bullet pullet to get that bullet back out!

    Jim G
     

    Brettmparker1

    I didn’t do it!
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    Apr 26, 2019
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    Yes, I guess there is some witchcraft, because I use the Redding .291" sizing bushing, and as the math I showed a few posts earlier shows (.291" minus (.0145"x2 wall thickness) - .2636" Hornady bullet OD), it makes for a "perfect" .0016" neck tension.

    And that .0016" neck tension is sufficient that when I screw up on BTO and make the cartridge too short, it takes MANY wacks with the inertia kinetic bullet pullet to get that bullet back out!

    Jim G
    I guess I start shit from time to time on here, not intentional. I guess to get your wack count down maybe if 2x4s weren’t so much money you could get a couple and practice nailing them together.

    live to type another day…. also if you haven’t learned by now that everyone on the hide is right so stop arguing.
    Hope you get a laugh out of this.
     

    JimGnitecki

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    Oct 24, 2011
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    Austin, TX
    I guess I start shit from time to time on here, not intentional. I guess to get your wack count down maybe if 2x4s weren’t so much money you could get a couple and practice nailing them together.

    live to type another day…. also if you haven’t learned by now that everyone on the hide is right so stop arguing.
    Hope you get a laugh out of this.

    Yeah, I did. :)

    Jim G
     
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