I want to up my reloading game.  Tell me about bushing dies.  I was looking at the Redding dies (223) but am unsure what bushing to purchase.  

Is it a trial/error on finding the right size bushing?  Is there a formula?  I'm guessing it depends on the brass, but where do I start?

Thanks for the help

If you are shooting from an AR or a factory bolt action?  You likely wont be able to see the difference on target, bushing vs standard.

If you are shooting from a custom bolt gun and you trim necks to specific thicknesses?  Then its worth looking at.  However, you may be further ahead with the easier method of just FL sizing without the expander ball in your sizing die and using a mandrel to set neck diameter/tension.

Just food for thought.

Measure a loaded round with a caliper. The subtract anywhere from .001 ~ .003.  That being said, variations is neck wall thickness can make a difference. Also, any semi auto should have greater neck tension because of how violent chambering is. Once of the things I have noticed is that there is a small section of the brass right where the neck & shoulder meet that does not seem to get sized. Not sure it really matters though.  

I have several sets of the bushing dies. If I was going to do it over again, I'd get Forester FL dies and then have them hone the internal dimension on the neck and set neck tension with a carbide mandrel. I had them do this to a 30 year old .308 die and it works perfectly now. It's a two step operation for sizing but not too bad on a progressive.

There are plenty of videos on choosing a bushing. Just watch a few of those, then look up a honed die.

Each brand of brass is going to have a different neck wall thickness.  
Redding has long recommended this for determining a bushing size.


If you are single loading in a bolt gun, then 0.001 neck tension will work....
If you are loading from a magazine in a bolt gun, then 0.002 neck tension would be good...
If you are shooting the ammo in a semi-auto...then 0.003 neck tension should do the trick.

Example...... let us say you measure 5 different loaded rounds of your "224 super duper" loaded in Diamond brand brass
Your average came out to be.....0.252"
But loading in WW brass your measurement average came out to be....0.248"


Diamond Brand brass loads - 0.252" since this is a bolt gun that you may or may not load from a magazine...your bushing sizes would be 0.251 and 0.250
WW Brand Brass loads - 0.248 would make bushings 0.247 and 0.246 the ones for that brass

I use the Redding bushing dies for almost everything and I pair them with a carbide expander ball.

For your existing die -

1.  Remove the expander ball or the entire stem.
2.  Measure the OD of a case fired in your rifle.
3.  Measure concentricity of body and neck.
4.  Resize a case.
5.  Measure the OD of the neck.
6.  Measure concentricity of body and neck.

7.  Reinstall the expander and resize the case (or another case), repeating the measurements.

All by themselves, these results convinced me to try bushing dies.  I was appalled by how much the "standard" die was reducing the case neck only to have the ball re-expand it.

8.  Seat a bullet and re-measure the OD of the neck and concentricity.  

You don't need neck-turned cases to benefit from improved concentricity, dramatically reduced working of case neck and easier sizing of the neck by the carbide ball.

Pick a bushing that allows the ball to size the neck but with minimal undersizing.

OP, even different lots of the same maker can need different bushings..Figure out what brass you have  and what it measures then plan on getting at least 2 sizes smaller than just the one you measured..Eventually you are going to end up with 5 to 15 bushings depending on how many different brass makers/lots you have...I have found sizing .001" smaller and using a mandrel die to finish necks is much better since pulling anything out of the neck( such as the normal button on the de-primer rod) is prone to pulling necks out of square with the cartridge, but I do anneal every single time.....Mandrels don't do that since they size going in....Also annealed/not annealed can also affect bushing size if the brass keeps springing back because it has work hardened and needs annealed....

Is this on a single stage press?

Do you have a universal decapper?

Do you already have a traditional full length resizing die with a decapping rod and expander ball?

The cheaper option might be to just pull the decapping rod assembly out of your full length sizing die.

Then use a Lyman M die to expand the neck to the correct size.  Especially if this is going to be shot through an AR.

Yes there is a formula.  I think this is it:

[(bullet diameter) + (2 X neck wall thickness)] - (0.002) = bushing diameter


But I could be wrong.   I think you could easily google it though.

The reason I asked if you were doing this on a single stage is because if you do use a universal decapper first, a decapping rod-less full length resizing die second, and then a Lyman M die third, then I just added 2 more cranks of the press’s handle to what is an already rigamarole-ish process.

If you have a Dillon 550/650/750 , then it would be really easy to set up an extra toolhead with those three dies.

That’s ASSuming you don’t have to trim.

This is largely what I do. Not for any particular reason beyond spending a fair amount of time some time ago pushing brass around to make wildcats or turn this brass into that brass, just kind of the zen I fell into.

Depending on your mandrel die, you can adjust a fair bit of neck tension, but less than bushing dies.

Here is an article on expander mandrels:

https://bulletin.accurateshooter.com/2019/05/precision-expander-mandrels-from-21st-century-shooting/

Whether those same exact guys at 21st Century are still in business….I have no idea.

One other thing some guys were doing was taking pin gauges:

Attached File


And “chucking” the correct size pin gauge into a collet style bullet pulling die.

If they were really handy, they would first radius one end of the pin gauge.

Then they would use the bullet pulling die AND the pin gauge together to expand necks.

That  title is misleading.

It should really read:  “STOP JUST ONLY NECK RESIZING YOUR BRASS!!!"

The Redding S die can be set up about 3 different ways:

1.  With the decapping rod/expander ball and whatever neck bushing it is just like a regular traditional full length resizing die.
2.  No decapping rod/expander ball and a neck bushing, it is both bumping the shoulders back and squishing the necks
3.  No decapping rod/expander ball and NO neck bushing, then it is only bumping the shoulders back.  How the reloader person gets the necks squished down…I guess… is gonna have to take an only neck sizing or neck bushing die.

EDITED.

.244" is what I recommend for .223. It achieves approximately .0035" of neck tension without the expander ball installed. I run a .221" expander ball to push any donuts to the exterior.

21st Century makes a set that runs these diameters:  .221, .2215, .222, .2225, .223, .2235, .224, .2245, .225
I think they got it covered, but that price, ouch.  I want to buy a set, but Id want like 3 sets minimum, and I can think of better things to spend my money on.

I just use a TiN coated Sinclair at .222" for my mandrel.  Its proven to work quite well, and didnt kill me on price.

I know full well the reasons for using a bushing die for wildcats and random ideas that pop into my brain when it decides to fart.  :)
I use a Redding bushing 6.5 Grendel die for making my 6mm Grendel brass, and a Hornady bushing die for my 6 CM as I wanted to test a few things an the set was really cheap on sale.  I do use SAC bushings as well, that actually was money well spent, I definitely like them better than the Redding bushings.

Pro tip - buy a Forster .223 full length sizing die and have them home the neck to .244". You will work the brass only .001" more than needed to seat the bullet firmly (.003" of neck tension) and dramatically reduce oversizing your case necks.

I keep forgetting those guys at 21st century are still around.

Just maybe you will work the brass slightly less.

If you can see a measurable difference in group size you will have to have a beyond outstanding rifle and ability.

I own redding 308 s die set it did nothing measurable group wise.
Just another rabbit hole imo