Expander mandrel and bushing die?

[Matt_3479]

So I’ve never used an expander mandrel and thinking of getting a few as I ran into my first major inconsistency. My question is, I run redding type s bushing dies and curious if I’m running a bushing for the goal of .002thou neck tension, what mandrel do I get? For instance If I’m running a .336 bushing for neck tension for my Norma, should I run a 306 mandrel then to maintain my .002 though neck tension or should I be under sizing with a bushing slightly say .003 thou then then open back up .001 thou with a mandrel?

 

[RegionRat]

Assuming your brass thickness is nothing dramatic, your numbers sound reasonable, however.

I have never liked getting "stuck" and would say it is best to have your bushing sets covered, as well as your mandrels. If you anneal on every cycle, you may find that the recipe is stable stays the same on every cycle. Sometimes you will find a trade between sizing down and using the mandrel will give a different seating force. The only way to respond is to have your options open.

 

[Howland]

Is 0.002" just what you want, or have you determined that 0.002" is the optimal interference fit?

If you keep only the current bushing and get only the 0.306" mandrel, any necks with below average wall thickness will give less neck tension.

 

[skeeljc]

The mandrel needs to expand the neck by .002" to be effective. Less than that and the brass will just spring back.

The key to using mandrels for the final size is to anneal before sizing every time.

 

[David Christian]

@Matt_3479, what are you doing to your brass during your reloading cycle? Have you tested the spring back in your brass? That would help you back into what size bushings and mandrels/pins you should have in your tool bag. Do you anneal or turn necks?

Measure the neck diameter before and after sizing and see how those numbers compare to the bushing dimensions (measure the bushing as the stamped number may not be accurate). For me, I anneal after each firing and find only .0005 of spring back in my brass.

Through trial and error on a .284, I experimented with 4 consecutive bushing sizes (.309 to .312) as well as with 5 different pins (.2820, .2825, .2830, .2835, .2840) and found the combination that gave me the most consistent and accurate results.

For a bolt gun, loading one at a time, I don’t believe in the .002 general rule of thumb after doing these tests. 20,000 loaded rounds and three years later I am still using the same combination. Necks skimmed to .014, .311 carbide bushing, .2840 carbide pin, leaving me with just the spring back of .0005 as my neck tension.

 

[D-4297]

I'm in total agreement with David on this one . The less you move your neck brass around , the more consistent it will be . I shoot TR with a .308 , No turn chamber . I use a .335 bushing , that takes my neck to .3065/.307 , followed by a .3075 expander . In other words , I'm getting approximately .0005 interference fit , also .

 

[skeeljc]

Gauge pins are the only way to determine what is happening to the neck ID. Measuring neck OD and subtracting measured neck wall thickness can induce error due to the measurement technique. A gauge pin measures the true ID. Measuring the loaded neck OD is the best way to determine the hold on the bullet because it accounts for the bullet compression.

 

[Ned Ludd]

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Just remember that when you squeeze a case neck down from the outside with a bushing, the brass spring-back will cause it to open back up around .0005" or so when it is removed from the die. When you open a case neck up from the inside with a mandrel, the spring-back works in the opposite direction, and it will cause the neck to close up around .0005" or so when the mandrel is withdrawn. If using the mandrel as the final sizing step, I like to re-size the cases first with a bushing that is approximately .001" to .002 smaller than what I would use if the bushing die were going to be the only re-sizing step. That way, the mandrel will actually do some work and open up all the necks equally. If the necks as sized by the bushing die are very close in diameter to what the mandrel will ultimately open them up to, I feel like you get a little more variability in the final product. Due to the brass spring-back closing back up the necks about half a thousandth when using a mandrel, you want a mandrel that is ~.0015" under bullet diameter if it is to be used as the final sizing step.

For example, I would normally use a 0.336" diameter bushing as the sole sizing step for Lapua .308 Win Palma brass, which gives very close to .002" neck tension (interference fit). In contrast, when I use a bushing die followed by a mandrel sizing step, I would go with a .335" or .334" diameter bushing first, then finish them off using a 0.3065" diameter mandrel as the final sizing step. It can certainly be argued that using a two-step process such as this works the brass more than a single pass with a bushing die. However, I anneal brass every firing and I have never noticed any issues whatsoever when moving the brass that extra little bit using a slightly smaller bushing followed by the mandrel. In my hands, it's not a limiting source of error. I can imagine it might be more of a problem if you first used a bushing that was .003" or .004" (or more) tighter than the mandrel would open the necks up. By going with a bushing that is only .001" or .002" smaller, the mandrel will open up every neck to a small degree, which I feel improves consistency in its use, but it shouldn't be grossly over-working the brass, especially if you anneal every firing.

 

[D-4297]

Nice post , Ned . You said it much better than I did .

 

[Catgunguy]

Thank you Ned. Very helpful.

 

[klamathsteel]

I have a Forster standard (non bushing) FL die for 6.5x47. When i size a case with the expander ball in
i get a neck ID of .262. If i take the expander ball out neck ID is .258. So can i use a mandrel to expand
from .258 up to .262 or is that too much ? I'm trying to lose the expander ball and still use the die i have.

 

[JimSC]

great post Ned. Yesterday I began experimenting with mandrel sizing and went .002 smaller on my bushings smaller than when not using the mandrels. So far I am pleased with the results

 

[Mark W]

I’ve been using a bushing die with an expander as the final step for a while now with my 6 BRA. After reading Ned’s post, I’m going to do do some math and see exactly how much I’m moving the brass. All that I know right now is that my seating became more consistent and the targets responded positively once I started my current process. I might have got lucky on my bushing and mandrel selection because I can see how it wouldn’t do anything if the bushing and mandrel are too close in size.

 

[Ned Ludd]

I’ve been using a bushing die with an expander as the final step for a while now with my 6 BRA. After reading Ned’s post, I’m going to do do some math and see exactly how much I’m moving the brass. All that I know right now is that my seating became more consistent and the targets responded positively once I started my current process. I might have got lucky on my bushing and mandrel selection because I can see how it wouldn’t do anything if the bushing and mandrel are too close in size.

Agreed. If the two sizing steps results in the case necks being very close to the same size, I've always felt that that led to greater variability/less consistency. The second of the two tools used, which can be the mandrel or the bushing (I've done it both ways), needs to do a little work to ensure consistency. Even opening the necks up just a thousandth or two seems to be enough. Of course, if the two steps leave the necks very close to the same diameter, it can also be argued that the second step is largely unnecessary and merely "extra work", although it is certainly possible to also improve the straightness/concentricity of the necks in the second step without greatly changing the diameter.

 

[skeeljc]

I am still learning about how to keep case necks concentric and in line with the case body. So far it seems that a one piece FL sizing die (w/o expander) produces the best results. Expanding the neck with a pin as a separate operation introduces some misalignment. A standard FL die reduces the neck diameter too much for good brass life. The solution seems to be to open the neck portion of the FL die to reduce how much it sizes the case neck. Then a pin can be used to expand the neck to achieve the desired neck tension. This means turning the case necks to a specific diameter for the FL die/pin setup.

Right now my thought is to size the neck OD to .003" below the loaded round neck OD with a modified FL die and then use a gauge pin to expand to the neck ID to achieve the desired neck tension. That way I can vary the neck tension by changing the expander pin size. Gauge pins are readily available in 0.0005" increments for around $5. Special order gauge pins are available in 0.0001" sizes for around $20 each.

 

[leclairk]

How do I determine what bushing size I need to buy for a FL sizer, assuming I want .003 neck tension? I need a bushing for my FL Whidden die. They say to measure a loaded round and subtract from that but I haven’t loaded any rounds. Should I measure a factory Hornady round and use that?

 

[skeeljc]

How do I determine what bushing size I need to buy for a FL sizer, assuming I want .003 neck tension? I need a bushing for my FL Whidden die. They say to measure a loaded round and subtract from that but I haven’t loaded any rounds. Should I measure a factory Hornady round and use that?

You need to seat a bullet in YOUR brass and then measure the neck diameter. This is because the size of the bushing needs to be based on YOUR brass thickness in the neck. Just size the neck enough to hold the bullet and create a dummy round. You can always pull the bullet and use the brass.

An alternate approach would be to use a neck thickness micrometer to measure your neck thickness. You need to average at least three measurements of neck thickness. Then add twice the neck thickness to the bullet diameter to get the loaded round neck OD.