Mandrel and bushing sizes

[chungus]

I have doing research and find a lot of significantly varying information. I know these are subjective to your desired neck tension but as a general guideline how do you go about choosing a mandrel and bushing size? I am currently using a mandrel three thousandths less than the bullet diameter and a bushing six thousandths less than the loaded neck diameter.

 

[RegionRat]

You might want to tell folks your basic caliber, and brand or thickness of brass, and the type of shooting context as well.

The actual values will depend on the above, plus the hardness state.

You can expect a little change (yield) but also a little spring back (elastic) when moving brass far enough to get into yield.

The bushing for a small caliber is one thing, and for a larger caliber would be different, and for a different thickness/hardness of brass would be different, etc. .... A -0.006 bushing would be a lot for a 223, but not for a 338... so it helps to be a little more specific with the context since some context can take very light seating force while others require more.

The target. seating force, or both are good feedback tools for your neck tension study. YMMV

 

[chungus]

Thanks. Lots of calibers. I am needing to buy mandrels and bushings for 22 creed, 6 dasher, 6 arc, 25x47 lapua, 6.5 creed, 6 PRC. I was previously using non bushing style dies with the expander ball but recently bought SAC dies for everything. Brass is alpha and lapua. I also anneal every firing. I understand that there will be some trial and error and I will probably have to tweak them for optimum results, but I am just looking for guidelines on what to order to start with.

 

[Rocketmandb]

I like to use a bushing such that the mandrel minimally engages the brass on each piece. My take on it is that the more you move the brass, the more springback will be introduced - and the more movement, the more opportunity for variance.

 

[TheOE800]

You might want to tell folks your basic caliber, and brand or thickness of brass, and the type of shooting context as well.

I just picked up some brass that seems fairly inconsistent not only from piece to piece but within the same case neck. Maybe I suck with the ball micrometer but in some pieces I was getting as much as nearly 0.002” total difference at various points on the neck. Some cases from 0.0142 to 0.16 some others 0.015 to nearly 0.017. What’s one to do with in this case?

 

[Rocketmandb]

I just picked up some brass that seems fairly inconsistent not only from piece to piece but within the same case neck. Maybe I suck with the ball micrometer but in some pieces I was getting as much as nearly 0.002” total difference at various points on the neck. Some cases from 0.0142 to 0.16 some others 0.015 to nearly 0.017. What’s one to do with in this case?

Here are your options:

1) Don't use that brass and get Lapua instead

2) Neck turn the brass

 

[TheOE800]

Here are your options:

1) Don't use that brass and get Lapua instead

2) Neck turn the brass

Yeah I figured those were my two options and they both suck.

 

[straightshooter1]

Yeah I figured those were my two options and they both suck.

At least with turning the necks, it's essentially a one time operation.

 

[rustyinbend]

I have doing research and find a lot of significantly varying information. I know these are subjective to your desired neck tension but as a general guideline how do you go about choosing a mandrel and bushing size? I am currently using a mandrel three thousandths less than the bullet diameter and a bushing six thousandths less than the loaded neck diameter.

I am blessed to have an AMP press, so I can "bushing down" and "mandrel up" to exactly the seating force that gives me the best results. For me ... the seating force from my AMP Press is the way I pick bushings and mandrels. It's a great new toy.

 

[padom]

I have multiple bushings and multiple 21st Century mandrel for each caliber. What bushing and mandrel combo you use is going to depend on the brand of brass, number of firings, annealed or not to get your final desired neck tension.

The first time I load virgin brass I will measure the loaded neck OD and record that number for that batch of brass with that bullet. I will then take once fired brass and measure the fired neck OD.

I will then pick a bushing i think will get my necks sized down to 0.004 under that loaded round neck diameter. I then size one piece of brass and measure the neck OD. If it's 0.004 under that loaded neck diameter we recorded earlier, perfect. If it's not, I will size another piece of brass with a larger or smaller bushing and measure again.

Once I have the right bushing that sizes those necks down to 0.004 under loaded, then I'll pick a mandrel and run that brass throught it and measure the neck again. If I want 0.002 final neck tension, then I'm looking for a mandrel size that gives me a final measurement of 0.002 under loaded neck diameter. If you want 0.001, or 0.003 neck tension then you pick a different mandrel and look for that final number under loaded neck diameter.

Now, because of springback you can use a smaller or larger bushing and different mandrel combo to get these different final neck tensions also. Which is what I did for years before companies came out with mandrel in 0.0005 increments...


Here an example if this makes it easier to understand


These numbers are not actual but will give you the picture of what to do for your brass..

say your loading for 223rem with LC matching headstamp brass and 80 smk in a bolt gun

I'll load that LC up with 80smk and measure the loaded neck...

Loaded Neck Diamter = 0.246"

I'll then fire it then tumble it. I'll then measure that once fired neck. This step has nothing to do with selecting a bushing or mandrel but gives me data on how much we are sizing down our fired necks..

Once fired Neck Diamter = 0.252"

Now, I select a bushing based off previous data in my database (or research what others use with this caliber and brand of brass as a starting point if i have no data on the combo in my database)

So I then size my once fired brass with a FL bushing die setup to bump the shoulder back 0.002 for bolt gun brass and use Say a 0.244" bushing..

I then measure this sized neck and it comes out 0.242 because of spring back... perfect that's 0.004 under my loaded round neck of 0.246... (IF it was less or more than 0.242 then I would have picked a smaller or larger bushing and sized another piece of brass until I found the right bushing)

I then grab say a 0.222 mandrel...that opens the neck up 0.002 and my final sized neck measures 0.244... thats 0.002 under my loaded round neck of 0.246 giving me a final 0.002 neck tension.

I have a box of bushings in multiple sizes for each caliber and a stand with multiple different size mandrels from 21st Century for each caliber I load for.....


Hope this helps or makes it clear for you

 

[RegionRat]

Thanks. Lots of calibers. I am needing to buy mandrels and bushings for 22 creed, 6 dasher, 6 arc, 25x47 lapua, 6.5 creed, 6 PRC. I was previously using non bushing style dies with the expander ball but recently bought SAC dies for everything. Brass is alpha and lapua. I also anneal every firing. I understand that there will be some trial and error and I will probably have to tweak them for optimum results, but I am just looking for guidelines on what to order to start with.

Okay, but get your checkbook out..... LOL

You have already heard some good advice above, and it is easy enough to buy a few bushings and mandrels bigger and smaller to try... but then what?

I would suggest you pick the rifle that lets you have your highest confidence and focus for a while on the neck prep. Pick just one caliber and tool up completely before you order for the rest. You may find you like one method for all, or you may end up with several methods based on context. Take it a step at a time and work on your skills using a test-mule before taking the plunge on all the others.

If you can run seating force measurements to get feedback it really helps.

Hopefully one of your list is a well behaved heavy barreled match gun that won't hurt you if you burn it up. A heavy section match barrel lets you shoot a lot without heating it up as fast as a lightweight carry gun.

I like to teach this by introducing it with a heavy section target rifle that allows the student to shoot far down the trajectory. This allows all of the speed and group characteristics to fully develop, but without getting into debates about how some bullets go through sonic transition and others don't.

It is counterintuitive to start with a rig where the sensitivity of brass prep is low, but it gives a valuable lesson when the next step is to run the neck prep lessons on a high-recoil lightweight carry rifle. One rifle can show the student how wide the window can run and makes it all look easy, and then other is humiliating.

Rather than humble them at the start, the easy rifle gets them a view of how the brass stress/strain relationship and the friction coefficient of the neck-bullet works.

These are lessons in material science and metalworking skills that are somewhat independent of internal ballistics and load tuning.

As an example, there are several tooling methods and yield approaches to get the same finished neck diameter.

You can minimally move the brass, or you can swing it up and down hard, ending up at the same neck ID. But, those methods change the work hardening history on the brass, as well as having their effect on the consistency of the whole batch. (Annealing can play a role, but don't do it if you are not good at it. Bad annealing is worse than no annealing.)

Just as a discussion example... If I use the concept of the Lee Collet die in 223 as an example..., when using a 0.222" diameter mandrel, the method does the minimum cold work to size the brass. It basically doesn't add any residual shear stress and only moved the brass down onto the mandrel. This is the least amount of extra yield and cold work to move the brass, just to illustrate.

At another extreme, we can us a bushing to force the neck into yield down to 0.219" and then open it with a mandrel back to 0.222"
With the elastic part of this, we would have to move below and above those diameters to get those values. A longer path to get to the same ending point.

So, how hard we push the neck diameters down and back up is up to us and rather than tell you what to do I will say you should play with all methods as a rookie and have the differences in your skill set. You end up having to test and shoot a lot before you can really understand the differences in cold work on brass, and how that affects dispersion and fatigue. There is always more than one way to skin a cat... context matters...

Don't forget to pay equal attention to the ID friction coefficient, and try to avoid over-cleaning the ID so you stay away from adhesive friction (cold welding) issues. That is a different rabbit hole for another day...

If at all possible, work with a mentor who is fully equipped to demonstrate the effects of neck prep and seating forces. Good Luck. YMMV

 

[padom]

The reason we use bushing dies and mandrels over straight FL sizing dies is the following. I want to be clear, FL sizing dies like the Forster FL Sizing die will produce excellent ammo. But, they are made to be used on ALL brands and types of brass so they work the brass WAY more than tailored bushing dies.

#1 - Bushing dies you can tailor sizing to work your specific brass minimally
#2 - You can control the amount of desired neck tension to test what shoots best in your rifle... 0.001, 0.002, 0.003, 0.004, etc
#3 - You can control runout to be very very minimal to virtually non-existent if your prep is solid
#4 - With the mandrel part, you can minimise case growth and ID irregularities by forcing the irregularities in the neck to the outside where it doesn't affect the bullet. Also, I have seen case lengths grow excessively and need more trimming PULLING an expander bull out vs pushing a mandrel in. This differs depending on amount of inside neck lube and how much the neck was squeezed down before the ball rips up through that neck...

People that argued with me about FL dies not working brass. I challenged them to take their Forster or whatever factory off the shelf FL sizing die and grab a once fired piece each of RP, LC, Lapua, Winchester, Norma brass or whatever brands you have and measure the necks.. Then, take the entire expander ball and decapping rod right out of that FL sizing die and size each case. Measure the necks.. Now, do the same thing again with each piece of brass with the expander ball/decapping rod in the die and measure the necks one more time.

You will see that these necks are being sized down WAY more than needed. Like 0.018 - 0.025 depending on the brass manufacturer.... Then they are being ripped back open a shit ton. This works that brass WAY more than necessary which in turn shorts brass life, causes case failures sooner effects neck tension, especially after firing a few times. These FL sizing dies are made this way so they will size ALL types of brass with different neck wall thicknesses...

This is the reason why many use specific FL bushing dies to only size those necks down what's needed and nothing more.. Then the mandrel step is used to a) set final neck tension and b) force everything to the outside for extremely straight and concentric bullets with virtually no runout....

 

[padom]

If you want to get into the Mandrel game and dont want to buy multiple sized mandrels for each caliber, buy 1 of these 21st Century Turning mandrels for each caliber you need. Many of us used these exact mandrels for years before companies started selling multiple sizes for each caliber.

These are 0.002 under bullet diameter. So you use the right size bushing to size 0.004 under loaded, then use this turning mandrel to open the neck back up 0.002 to give you 0.002 final neck tension. Cheaper way to enter into the mandrel game, works great, makes excellent ammo and WAY cheaper than buying sets of mandrels for each caliber.. $37.50 each..

Black Nitride Turning Arbor (Black Nitride Turning Arbor: 22 Cal)

21stcenturyinnovation.com

 

[padom]

Looking at your caliber list

If using Starline brass for 6 ARC, I use a 0.248 Redding TiN bushing
6.5cm I use Norma Match brass.. I use a 0.289 Redding TiN bushing but 0.290 is popular also depending on brass..

I cant help you with the others as I dont shoot those calibers.

 

[RegionRat]

I just picked up some brass that seems fairly inconsistent not only from piece to piece but within the same case neck. Maybe I suck with the ball micrometer but in some pieces I was getting as much as nearly 0.002” total difference at various points on the neck. Some cases from 0.0142 to 0.16 some others 0.015 to nearly 0.017. What’s one to do with in this case?

Well, without knowing the specifics of the brass I would guess it is pretty low quality stuff.

We don't start rookies with neck turning, we let them get started with no-turn chambers. This is to let them get the hang of metal working and ballistics before we take them into situations where the chambers require turned necks.

In the same context, we do try to show them examples of brass being made and how poor tooling and press maintenance can lead to runout in the body of the brass that ends up in the necks.

If you try to make a silk purse out of a sow's ear, be prepared with your sorting and turning skills. Otherwise, leave that stuff to folks with cheap labor and lots of time on their hands.... In my era, we had no choice but to learn to make junk work, but these days you can skip all that.

When you dive into the rabbit hole of neck runout and low brass quality, you accept the role of brass inspector and will need to work on your metrology skills.

You can skip all that and just buy known high quality brass, but everybody has a problem on a statistical basis. Working with higher quality brass just means that statistic is rare. I am being long winded to say you should probably still know how to inspect brass even if you only buy the best. It just doesn't need to be a pre-requisite skill like it was when I started out.

Learn to measure brass neck thickness over the seated bullet, as well as playing with the ball mic on necks. The differences teach you about surface roughness, waviness, and lay of the profile. Both ways are important, but if you don't have the background I would encourage the dimension over the bullet and de-emphasize the ball mic method for a rookie to give them time to get used to measurements. YMMV