Redding Bushing Selection Help

[mjphawk]

For those that reload for precision long range. I have a question regarding bushing selection for the Redding Neck Sizing Die. I am attempting to size my necks to get approximately 0.001" smaller than the bullet diameter (0.308").

The attached images are Lapua brass which was previously fired in my gun using a 0.338" carbide neck bushing. I believe this to be too tight since at time small shavings of the jacket were being scratched off of the bullet.

It seems as though the neck is slightly flared at the top where I am getting a 0.340" measurement and slightly smaller in the middle of the neck at 0.338".

My concern is that if I go up to a 0.339" or 0.340" bushing that I will not have enough neck tension after allowing for spring back.

Any help is appreciated.

Pictures are measurement of 1) middle of neck, 2) top of neck, 3) bullet just above neck (to ensure calibration), and 4) neck using micrometer (additional check for calibration, contacts at top of neck).

 

[mdmp5]

The case mouth will show a larger measurement than the neck if it is not adequately deburred

 

[mjphawk]

The case mouth will show a larger measurement than the neck if it is not adequately deburred

I chamfer and deburred the cases but I guess I need to get more aggressive?

Any thoughts on the proper busing size? If you are indicating that the mouth may be flared out because of inadequate case prep that would mean that the measurement I am taking off of the center of the neck is more accurate. The middle of the neck measures 0.338" and I am using a 0.338" bushing which would indicate zero neck tension when in fact the tension I have is rather significant.

 

[Milo 2.5]

I chamfer and deburred the cases but I guess I need to get more aggressive?

Any thoughts on the proper busing size? If you are indicating that the mouth may be flared out because of inadequate case prep that would mean that the measurement I am taking off of the center of the neck is more accurate. The middle of the neck measures 0.338" and I am using a 0.338" bushing which would indicate zero neck tension when in fact the tension I have is rather significant.

Try a couple with an aggressive chamfer, unless you've trimmed the brass, the outside(deburring) of the case takes care of itself through firing and sizing, your case mouths may be yielding a false sense of tension.
I was running a .336" bushing on a 300 Norma case, which has to be thicker for comparison.

 

[mdmp5]

I haven't loaded 308 in quite some time. From memory, with Lapua brass, 336 was the correct bushing. I think that have me 2 thou of neck tension.

yes, check your chamfering and deburring . Actualy, a chamfer does not need to be deep at all. I just give it a light touch unless I need to trim, which gets done in the giraud. However, the deburring will leave a small lip on the outside of the mouth. Run your finger over it and if it feels like a little rough step, that is why you are measuring big.

im having a hard time articulating exactly what I mean about the deburring, but I understand what you are seeing

 

[DynamicAccuracy]

Measure in multiple spots on the neck and mouth and average them out. If you have .001 neck tension you'll barely feel it seating the bullet at least I dont anyways

 

[mdmp5]

Measure in multiple spots on the neck and mouth and average them out. If you have .001 neck tension you'll barely feel it seating the bullet at least I dont anyways

Neither will .002. I wouldn't average out anything. I would get the mouth as clean as I can and then the tension should be universal in any spot on the neck

 

[Sheldon N]

If you're shaving the bullet jacked on seating, you need more champfer/debur as noted above.

I personally like to measure the neck just below the rim to get a clean and flat surface to check. As long as you measure in the same place on both the sized empty case and the case with the bullet in it you should get good comparative measurements.

Biggest thing though is to measure the cases after sizing to see what your actual results are. What's printed on the bushing doesn't matter, what matters is what comes out of the die. I've seen Redding bushings produce results that were 0.001 - 0.0015 smaller than the printed number on the bushing. Total amount of sizing, brass hardness, annealing, and bushing to bushing manufacturing variation can all affect what results you get.

 

[Rob01]

From what you are showing they the .336 bushing for .002" of neck tension. It's what I used years back for one of my lots of Lapua brass. The other was a .335.