Neck mandrel question

[Zack_va248]

Started using a K&M neck mandrel and noticed on seating it’s smooth and then a bit of crunch/tension

Measured my neck about 1mm below the mouth and had .290”, perfect .002” for my 6.5 creed. However the neck just before the shoulder junction is .287” so I’m .003” more neck tension at the base of the neck.

The mandrel tapers to a max diameter of .264” when it goes flat and there’s not enough bearing surface on the mandrel at .290” to size the entirety of the neck.

My question is where are you guys measuring your necks for those using a k&m mandrel and is it ok to set the tension at .002” just before the shoulder? Leaving the neck slightly opened up at the mouth?

I don’t feel that’s correct. I believe that I should have the neck be consistent all the way down at my desired .002” under seated bullet size. Please correct me if I’m wrong. Thanks in advance gents.

 

[KnowNothing256]

Sorry, to confirm my understanding: you’re saying that the portion of the mandrel that’s 0.262” (but I think you said 0.264”?) is shorter than a 6.5CM neck?

 

[Zack_va248]

Sorry, to confirm my understanding: you’re saying that the portion of the mandrel that’s 0.262” (but I think you said 0.264”?) is shorter than a 6.5CM neck?

Correct. The taper is too fast at .262” to size the full length of the neck without opening the case mouth further.

 

[Steel head]

Basically it sounds like you have a donut situation caused by your mandrel or it’s in the brass.

You really don’t want that.
You want the neck doing the retention not a tight spot, especially near the neck shoulder junction.

I started making my own mandrels and I have a longer full diameter area so I have no issues like that or have to bottom the mandrel shoulder into the neck to get full sizing.

 

[Zack_va248]

Basically it sounds like you have a donut situation caused by your mandrel or it’s in the brass.

You really don’t want that.
You want the neck doing the retention not a tight spot, especially near the neck shoulder junction.

I’m going to switch to a straight mandrel like the 21st century and run it at a .262” and see how that works in comparison.
My Redding dies did a great job at keeping
it consistent but I wanted to try out using a mandrel to see if it made a difference in sd/es

 

[IHFarmer07]

Basically it sounds like you have a donut situation caused by your mandrel or it’s in the brass.

You really don’t want that.
You want the neck doing the retention not a tight spot, especially near the neck shoulder junction.

I started making my own mandrels and I have a longer full diameter area so I have no issues like that or have to bottom the mandrel shoulder into the neck to get full sizing.

Yep, my first thought, donut, pretty sure if you have a neck tension issue it’s a donut issue......only good way to get rid of them is to neck turn into the shoulder just a touch.

 

[2aBaC̶a̶]

Stupid question but can you screw the die down further so the mandrel goes deeper? Hard to belive they would make a mandrel for only part of the neck.

 

[Steel head]

Stupid question but can you screw the die down further so the mandrel goes deeper? Hard to belive they would make a mandrel for only part of the neck.

I’ve seen a few quite short but always enough to get the job done.

 

[Zack_va248]

Stupid question but can you screw the die down further so the mandrel goes deeper? Hard to belive they would make a mandrel for only part of the neck.

No, the taper goes up to .264" before it levels off to straight. If I go further the case mouth will be opened up to caliber sized.

 

[Steel head]

No, the taper goes up to .264" before it levels off to straight. If I go further the case mouth will be opened up to caliber sized.

It sounds like you have a bad mandrel or some other issue happening

 

[Zack_va248]

It sounds like you have a bad mandrel or some other issue happening

Agreed. I just wanted confirmation from others that this isn't how the mandrel should be.

 

[Steel head]

I drew this with my advanced dick drawing skills.
This is what most of my purchased and self made mandrels look like.
Generally there’s 1.5 neck lengths of full diameter shank to work with.

 

[spife7980]

I drew this with my advanced dick drawing skills.
This is what most of my purchased and self made mandrels look like.
Generally there’s 1.5 neck lengths of full diameter shank to work with.

View attachment 7588706

Hes got k&m

OP, that shank cylinder should be .262, not .264

 

[Steel head]

Hes got k&m
View attachment 7588711
OP, that shank cylinder should be .262, not .264

Interesting
Obviously that’s a case stop?
Not a lot of real estate but enough and yes a .262 is what should be used.

 

[spife7980]

Interesting
Obviously that’s a case stop?
Not a lot of real estate but enough and yes a .262 is what should be used.

Yeah, case stop to index off of and to not crush the mouth. Always seemed like a dumb design to me.

 

[Steel head]

Yeah, case stop to index off of and to not crush the mouth. Always seemed like a dumb design to me.

Yea I just make the shank longer and let the press be the stop.

I’m guessing OP has a 264 mandrel and is trying to use the nose.
He’s playing with the tip!

 

[Zack_va248]

Yea I just make the shank longer and let the press be the stop.

I’m guessing OP has a 264 mandrel and is trying to use the nose.
He’s playing with the tip!

Hes got k&m
View attachment 7588711
OP, that shank cylinder should be .262, not .264

Unfortunately the only option they have on their site was for a "6.5" with no specificity to what desired tension you want. I suppose they aren't wrong. It is a .264" mandrel. But I want the max shank at .262" so I can run the full length of the neck up on it and done.

 

[2aBaC̶a̶]

No offense OP but my first inclination when something doesnt work is user error.

Just so were all clear.

Are you saying that at the part where the taper starts (red)measures .262" but by the time it gets to the end (green) its .264"?

 

[Zack_va248]

No offense OP but my first inclination when something doesnt work is user error.

Just so were all clear.

Are you saying that at the part where the taper starts (red)measures .262" but by the time it gets to the end (green) its .264"?

View attachment 7588744

No, the from the beginning of the tapering up to the red line is .262" then the flat from red to green is .264"
That's why I can't get the necks to be consistent all the way through. It's only .262" for a very very small section. Maybe .100" worth
I agree with you though. Most often it is user error. I just didn't see any possible way I was wrong here. I even checked the measurements with three different Mic's to verify that wasn't the issue.

 

[2aBaC̶a̶]

No, the from the beginning of the tapering up to the red line is .262" then the flat from red to green is .264"
That's why I can't get the necks to be consistent all the way through. It's only .262" for a very very small section. Maybe .100" worth
I agree with you though. Most often it is user error. I just didn't see any possible way I was wrong here. I even checked the measurements with three different Mic's to verify that wasn't the issue.

Ok got it. In that case yeah sounds defective.

 

[TheOfficeT-Rex]

Sounds like the wrong size mandrel for what you want. The 'flat' section should be doing the final sizing, not the tapered bit.

Having seen that, I think I like the sinclair/21st century mandrel designs better. They look like the dick drawing above and have plenty of long, flat shank for full sizing. The 21st black nitride ones are pretty smooth for the price.

 

[Steel head]

Sounds like the wrong size mandrel for what you want. The 'flat' section should be doing the final sizing, not the tapered bit.

Having seen that, I think I like the sinclair/21st century mandrel designs better. They look like the dick drawing above and have plenty of long, flat shank for full sizing. The 21st black nitride ones are pretty smooth for the price.

 

[whatsupdoc]

OP you need to adjust your mandrel so that the edge of the case mouth ends up at the green line in the picture above.

The stop screw is hitting the bottom of the case and preventing the mandrel from completely expanding the case.

 

[Dave62677]

just get the 21st century mandrel which you can choose the proper neck tension size.

 

[2aBaC̶a̶]

OP you need to adjust your mandrel so that the edge of the case mouth ends up at the green line in the picture above.

The stop screw is hitting the bottom of the case and preventing the mandrel from completely expanding the case.

The problem is that the expander body between the red and green lines is a full .264 instead of the .262

 

[Joel Danielson]

The K&M mandrels are not made to be tension setting devices (some have tried to make them be). They were originally used to open up new cases prior to being turned for neck thickness.
Get one of the 21st Century systems and be done. You can order several sizes if you want to play with neck tension for better consistency and vertical in your LR shooting.
Here's another system that is really good: https://portersprecisionproducts.com/expander-mandrel-die/
Cheers

 

[whatsupdoc]

The problem is that the expander body between the red and green lines is a full .264 instead of the .26

Ok got it, missed that.

 

[2aBaC̶a̶]

The 21st century looks legit and you can order mandrels in .0005 incriments.

I use the sinclair one which is basically the same. Speaking of which I need to try the TiN coated becase the SS one causes galling when small brass deposits on it.

 

[jmw]

The Sinclair carbide mandrels are the best I’ve used

 

[Dave62677]

I apply a very thin layer of hornady one shot on the 21st mandrel every 10 cases. I also apply a thin layer one shot on the lower part of the bullet. I notice my arbor press seating pressures are way more consistent. My last batch of load avg 8 ES. Some said it is not necessary but I do what I made myself feel good.

 

[Recon Marine]

The 21st century looks legit and you can order mandrels in .0005 incriments.

I use the sinclair one which is basically the same. Speaking of which I need to try the TiN coated becase the SS one causes galling when small brass deposits on it.

I use the tin coated Sinclair with no problems. Carbides are outrageously priced.

 

[Tokay444]

You can’t have a taper that’s .262”. It’s either ___” to .262”, or .262 to ___”.

 

[KnowNothing256]

You can’t have a taper that’s .262”. It’s either ___” to .262”, or .262 to ___”.

Thanks for adding exactly nothing to the troubleshooting process. Which, by the way, has already been figured out, as the thread comments make clear.

Keep up the good work.

PS: And if you wanna get so dang technical, a taper defined as you described would also require a length, as in 0.262” to 0.264” over 0.150”. The least you could do is nitpick *well,* sheesh.

 

[Tokay444]

Of course there’s a length.

 

[2aBaC̶a̶]

Rough crowd.

 

[Steel head]

The 21st century looks legit and you can order mandrels in .0005 incriments.

I use the sinclair one which is basically the same. Speaking of which I need to try the TiN coated becase the SS one causes galling when small brass deposits on it.

They are nice.
They make a lot of nice stuff.

 

[never_summer]

Expand Mandrel for Bullet Tension

Expand Mandrels for Bullet Tension expand the case neck so the brass will spring back to the correct size needed for seating bullets.

kmshooting.com

K&m makes a custom mandrel, I use these in my 223 and 6bra with good results. They don’t take a horrible amount of time to be delivered and once the stem is set it doesn’t really matter how far you set the die. Wish they had carbide like my Sinclair was but that’s my only gripe