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Discussion Starter · #1 ·
I searched the forum and read till my eyes were crossed. I’m a little confused on the bushing size needed for the 6.8 Redding type s FL die……both my starline and S&B brass with a loaded 105 CBB MKZ (resized using rcbs SB die with decapping rod removed, and .275 21st century expander mandrel) measures .295. Redding instructions state to subtract .01 from that and order that bushing, which would be .294…….but the threads that I read state that they use a .300 bushing.

I really don’t want to waste money buying 8 bushings. Two or three maybe, but not 8.

Can someone please quell my confusion?
 

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I'm not sure I will be much help. My 105 MKZs measure 0.302" in S&B brass while 120 SSTs measure 0.301". I use a 0.300" bushing which is 0.001" smaller than the loaded SST. It still works ok for me with the MKZ because I found the tighter neck seats the bullets better with their groove/bands on the bullet shank. Even with a 0.002" thinner case neck on Remington brass (0.004" diameter). I haven't seen measurements that small. Are your calipers measuring correctly?

Another way to work this is

bullet diameter + 2x neck thickness - 0.001" = desired bushing diameter

Also, this bushing diameter is for running the Redding Type S die without an expander ball which improves concentricity and reduces work hardening of the brass.

I also run a mild crimp with a dedicated Lee collet crimping die with the 0.300" bushing.
 

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Discussion Starter · #4 ·
I'm not sure I will be much help. My 105 MKZs measure 0.302" in S&B brass while 120 SSTs measure 0.301". I use a 0.300" bushing which is 0.001" smaller than the loaded SST. It still works ok for me with the MKZ because I found the tighter neck seats the bullets better with their groove/bands on the bullet shank. Even with a 0.002" thinner case neck on Remington brass (0.004" diameter). I haven't seen measurements that small. Are your calipers measuring correctly?

Another way to work this is

bullet diameter + 2x neck thickness - 0.001" = desired bushing diameter

Also, this bushing diameter is for running the Redding Type S die without an expander ball which improves concentricity and reduces work hardening of the brass.

I also run a mild crimp with a dedicated Lee collet crimping die with the 0.300" bushing.
You nailed it. Luckily I have 3 sets of calipers. The one I was using had a low battery so I replaced it and checked my measurements again with all 3 micrometers, including an old dial mic thats 20+ years old. Makes me want to spend the coins on a quality mic instead of the ones I have.
Feel like an idiot. My measurements on both starline and S&B brass with my loads were at .303-.302 out of several rounds measured with all three of my mics.
Looks like everyone else was right and I’m an idiot for not checking my mic for accuracy.
 

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That's a good idea. I have two sets of weight standards for my beams and e-scales. They would work for the lower end of the measuring range of the mics, and upper range of the calipers. I have feeler gauges that work for the calipers lower range, but for the mics upper range I have some dummy/snapcaps that'll be perfect for the mic's upper range standards.
 

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Here is a formula I found somewhere. Neck wall thickness X 2 + bullet diameter = ___ Next subtract .002 to .003 from that number for the bushing size. Hope that helps.
 

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This is the information related to me by another member some time ago.

The 300 is fine and is what I used for a long time, my brass is getting old and the necks are a litlte thinner so I just went down to a 299 bushing to to give it about .002" neck tension after the expander pulls through.

.299 bushing - .024" neck thickness = .275" neck ID/Tension
or
.277 bullet + .024" neck thickness = .301 - .002" for tension = .299 bushing
or
.301" loaded round - .002" neck tension = .299 bushing

but most brass is closer to .026" thick(.013*2=.026") so in most cases a 300 bushing is perfect.

300 bushing - .026" neck thickness = .274" neck tension (.003" tension is better in an AR)
or
.277" bullet + .026" neck thickness = .303 - .003" neck tension for a .300 bushing
or
.303" loaded round - .003" neck tension = .300 bushing(this is the easiest way most people figure their bushing size but you have to take into account how much your expander opens the neck back up after the neck is sized, say your using a .300 bushing with brass with a .026" thick neck that should give you .274" neck ID for .003" neck tension but if the expander opens the neck back up to .275 you just lost .001" of your neck tension and can go down one more bushing size to make up for this because brass usually only springs back .001" so if your .001"' smaller than you want it will end up just right in the end.
 
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