Do you mandrel after using an FL bushing die?

[Castle Rock]

I just use the expander in the die along with a bushing that doesn’t over work the neck.

 

[EE_Reloader]

I use FL bushing dies and then run a mandrel afterwards. If you have any variation in neck thickness then you will have different neck tension as the bushing will push that variation to the inside of the brass. I use a mandrel .002" smaller than bullet diameter and that gives me a more consistent neck tension as that pushes any variation to the outside of the case. There was more thought placed into this but unless someone wants to hear the ramblings of an overthinker, I'll keep it to myself.

 

[Treelineasassin]

I use FL bushing dies and then run a mandrel afterwards. If you have any variation in neck thickness then you will have different neck tension as the bushing will push that variation to the inside of the brass. I use a mandrel .002" smaller than bullet diameter and that gives me a more consistent neck tension as that pushes any variation to the outside of the case. There was more thought placed into this but unless someone wants to hear the ramblings of an overthinker, I'll keep it to myself.

002 under mandrel, often referred to as a turning mandrel, typically leaves 0025 nk tension. Let's use lapua 6cm for example. Loaded nk OD is 273. Prior to seating bullets, your mandrel had set the nk of to 2705. What size bushing in your process, is being utilized, 269? This is all just theory based for numbers.

 

[EE_Reloader]

Normally I start with finding the brass case neck thickness. Let's says it's .015" for simplicity sake. I have the diameter of 6mm (.243"). So I take .243" + (.015"x2) there are 2 sides of brass. So now we have a final loaded measurement of .273" I will normally pick a bushing that is .003" -.004" smaller than .273" so .269 to .270. I will then run a .241" mandrel down the brass. Sizing using a .269 to .270 bushing guarantees that the mandrel will engage and set your final neck tension. How the brass behaves after the fact is based on several other things that I won't get into here but for me, I want consistency in the process.
This is all based on the assumption that the brass is 15 thousandths all the way around for this math to work. However if you start having a lot of neck thickness variation, which you can get in lots of brass (won't name any here), then the process start to fall apart. The brass might not get sized down enough (if its thinner than 15 thousandths) for your mandrel to engage, etc.

 

[Treelineasassin]

Normally I start with finding the brass case neck thickness. Let's says it's .015" for simplicity sake. I have the diameter of 6mm (.243"). So I take .243" + (.015"x2) there are 2 sides of brass. So now we have a final loaded measurement of .273" I will normally pick a bushing that is .003" -.004" smaller than .273" so .269 to .270. I will then run a .241" mandrel down the brass. Sizing using a .269 to .270 bushing guarantees that the mandrel will engage and set your final neck tension. How the brass behaves after the fact is based on several other things that I won't get into here but for me, I want consistency in the process.
This is all based on the assumption that the brass is 15 thousandths all the way around for this math to work. However if you start having a lot of neck thickness variation, which you can get in lots of brass (won't name any here), then the process start to fall apart. The brass might not get sized down enough (if its thinner than 15 thousandths) for your mandrel to engage, etc.

Got ya, sounds similar to my workings. Inconsistent necks, I size down a bit more with the bushing, to guarantee all the consistencies are pushed out by mandrel, thanks for detailed response. Even wirh lapua and Alpha, I still find 001 variation of neck thickness measuring several quadrants of the neck well using a tuning micrometer.

 

[BBob]

So kind of like (or exactly like) seating depth testing. How many have actually tested and can prove that using a mandrel does anything to improve your groups? I suspect it's a feel good, I think it does sort of thing. I've done my own testing and as far as doing it to improve grouping I don't do it (anymore).

 

[dfirkus83]

I size down 4 thou under bullet diameter with a bushing and set tension with a mandrel. Works well for my setup.