Type S bushing choice.

So I know the rule is take a loaded round O.D. And subtract 1.5 thou and this should be your neck bushing size. But here is where I don't understand the logic. What if your sizing down brass and the brass neck is thicker? And I don't need to trim the necks because the chamber has more headspace allowing for this. I tried this method and put a carbide expander ball to see how much to touched on the way down. I was quite surprised.

You should typically have .003 - .004 gap between your reamed chamber and your brass neck. If you are shooting a .308 variety, the bullet is .308, then measure your brass thickness, for example .016 multiply that times 2 (both sides) that equals .032, add that to the bullet diameter and that nets out to .340. That would be perfect if your chamber was .343 - .344 and that is the fundamental measurement. The neck sizing bushing is for sizing for the correct neck tension, that is why folks suggest to measure your OD then minus .002 -.003. that will apply that amount of tension to hold the bullet in the case but you have to get the brass neck size correct first before you take that measurement. I hope that makes sense.

That does make sense. I just took a quick measurement of my brass it was
.0015 thick X 2 .0030
Bullet is .264
so .294 bushing?

Rhovee said:

That does make sense. I just took a quick measurement of my brass it was
.0015 thick X 2 .0030
Bullet is .264
so .294 bushing?

Click to expand...

Nope, that gives you no noticeable tension on bullet. You need a .292" bushing for .002" tension or .291" for .003" tension. This assumes your neck thickness measurements are spot on.

Ya that's the interesting thing. It seemed like I had to much on a .293 bushing when seating bullets so I attached a carbide 6.5mm expander ball and it was catching quite a bit on the way down.....

Your expander has more to do with neck tension than bushings. The bushing is primarily used to size the neck down so when the expander comes back through the neck on the up stroke it is the desired sizefor grip around the bullet. Example that is why most expanders say on a .264 cartridge are around .262 the thicker the neck on a .264 the bigger the bushing otherwise if you use to small a bushing your just over working the brass. If you use the same expander and just change bushings your inside neck dia. will still be the same. That is why expander kits are becoming more popular

Rhovee said:

What if your sizing down brass and the brass neck is thicker?

Click to expand...

Then your loaded neck OD is larger, leading to different size bushing need.

Rhovee said:

And I don't need to trim the necks because the chamber has more headspace allowing for this. I tried this method and put a carbide expander ball to see how much to touched on the way down. I was quite surprised.

Click to expand...

Nonsensical.

Um, I might be somewhat lost or is there a math error. If a .308 with brass thickness .016 would net out at .340. Wouldn't the .264 with case neck of .0015 not be a net of .267? Or was the .0015 measurement suppose to be .015?

"If you are shooting a .308 variety, the bullet is .308, then measure your brass thickness, for example .016 multiply that times 2 (both sides) that equals .032, add that to the bullet diameter and that nets out to .340."

".0015 thick X 2 .0030
Bullet is .264
so .294 bushing?"

he was just off on his decimal i think he meant .015

First it would be best if we knew the throat dimension, If you haveza custom barrel ask the people who chambered, if you dont know what is SAMMI spec for your round. Start there and then make your brass fit to give you .003 - .004 tolerance.

Yes my math was off with a decimal point. I could try and get a picture of the reamer. I did notice with a .293 bushing that once I resize once fired brass it does just barely touch the expander button. On virgin it pulls through with some resistance. I then do a quick stroke back over to even them out. I have read that getting the correct bushing and getting rid of the ball is ideal. Doesn't your case neck diameter change once the neck gets stretched and trimmed?

I turn my necks on a few different rifles and they seem to stay about where i turn to. Sometimes I will go back over them after I shoot them , I know some guys say that is not good but I have good luck, I like the expander to iron it out from the inside and get any dings out from extraction or whatever else pushes them in. all of the rifles i shoot i do very minimal bumping if any, so I dont trim much at all. I do have a rifle that whiddon made my custom dies and with the correct bushing that expander just barely hits it

You need to remove the expander here, using the bushing will tighten the neck but then you bring the ball up and destroy that good work, remove it to keeps things under control.

At the Redding website they recommend using a bushing a couple thousandths smaller if you do not neck turn your brass and use the expander that comes with the Redding bushing die.

Tech Line & Tips (FAQs)
Bushing Selection
http://www.redding-reloading.com/tech-line-a-tips-faqs/140-bushing-selection
"The above methods of determining bushing size require that the cases being sized have a fairly uniform neck wall thickness or have been neck turned. If the neck wall thickness varies more than 0.002", it may be necessary to use a bushing a couple of thousandths smaller than your calculations indicate, and then use a size button in the die to determine the final inside neck diameter."

On top of this brass spingback will effect the inside neck diameter, meaning there is no perfect bushing size. And you need several bushings to cover your sizing needs.

Example the Forster bushing bump die in .308 comes with three bushings.
Bushings included: 0.336", 0.334", 0.332"