Mandrel expander die question

[JS624]

Hey guys I know this I'm probably a dumb question but I just recently bought the k&m mandrel expander die set up.
so I'm using whidden FL bushing dies as I understand it the bushing sizes the O.D. of the brass to a specific dimension where as the mandrel does the same but to the I.D of the brass.
so where I'm confused is if I should remove the bushing from my die or not? I've heard the bushing moves any brass imperfections to the I.D of the brass which is not ideal.
so my other question is if I remove the bushing what sizes the the brass down so I can in turn expand it with said mandrel?
sorry if this is a little confusing. I'm a little confused myself.
thanks

 

[MtnCreek]

Size the neck with the bushing, then use the expander mandrel.

 

[flyright]

Use the largest bushing you can so that the mandrel is barely touching when in comes back through. This reduces the working of the brass and helps to minimize run out.

 

[Fursniper]

Size the neck with the bushing, then use the expander mandrel.

^^^This^^^

 

[Sheldon N]

Measure the OD of the neck after sizing with the bushing die, then measure the OD of the neck after running the expander mandrel through. IMO the goal should be that the before and after should be about 0.001 apart, bushing die squeezes it down 0.001 too far, then the mandrel die expands to the final desired size.

You'll probably need a bushing that is ~0.003 smaller than the neck OD of a loaded round.

 

[_Raining]

Measure the OD of the neck after sizing with the bushing die, then measure the OD of the neck after running the expander mandrel through. IMO the goal should be that the before and after should be about 0.001 apart, bushing die squeezes it down 0.001 too far, then the mandrel die expands to the final desired size.

You'll probably need a bushing that is ~0.003 smaller than the neck OD of a loaded round.

^^^This. Expanding mandrel should give 1 thou tension, turning mandrel should give you 2 thou tension.

 

[JS624]

Measure the OD of the neck after sizing with the bushing die, then measure the OD of the neck after running the expander mandrel through. IMO the goal should be that the before and after should be about 0.001 apart, bushing die squeezes it down 0.001 too far, then the mandrel die expands to the final desired size.

You'll probably need a bushing that is ~0.003 smaller than the neck OD of a loaded round.

thanks sheldon!

 

[JCCinOhio]

and... if you're reloading for a semi-auto, you may want to get a custom expander mandrel. I found -.002 was a little too little neck tension and had a custom -.0035 one made by pma tool. Went from pulling my hair out (didn't have much to start) to .5 moa groups at 185yds (furthest I can shoot at home). (for .308 SA)

 

[shoot4fun]

First, you are correct that the bushing will push irregularities to the ID of the neck. That could cause things that are not desirable. So, you're really thinking about this and that's good.
Now for my dumb question of the day.
Doesn't your FL die have an expander ball?
The ones that come in Whiddon dies are very good and he sells kits with different sizes if you really want to get picky. The Whiddon expander ball seems to be better about the "dragging" issue but using Redding Dry Neck Lube will absolutely take care of that and has been known to help reduce fliers (especially if you use SS media for cleaning).

 

[nexusfire]

I ditched the expander on my bushing die when I switched to the mandrel. You can get run out if the rod is not straight.

 

[JS624]

Thanks guys

 

[Wayne McNeely]

Fortunately, your Whidden die sizes the full length of the neck. Simply run your brass through the size die, then run the case over the expander to get the proper ID for turning brass. I would add, most people turn necks on new brass so as to get the most benefit from the brass. After doing all this sizing up and down, don’t forget to anneal, as this will work harden your brass and will lead to necks splitting.

Wayne