6.5 GAP 4S - Hornady v. Redding Dies with regards to neck sizing

[grizzlestomp]

GA Precision is building me a 6.5 RSAUM rifle and I am trying to decide if I need both bushing and nonbushing dies to properly neck turn cases.

6.5 GAP 4S (SAUM) Comp Die set with bushings (either .289 or .291 bushings) OR
Hornady 6.5 GAP 4S Custom Die Set w/ Micrometer Stem (non bushing)

I was leaning towards the Redding die, but I plan to neck-turn my brass and as I was researching that I found an article stating that non-bushing dies should be used before neck sizing. Then a bushing die is used to resize to achieve precise neck tension.

Plan on using the Hornady 6.5 GAP 4S brass. Chamber is being cut with new .120 FB reamer.

Can anyone comment on this? More generally, appreciate any feedback on which route to go. Thanks.

http://www.6mmbr.com/neckturningbasics.html
Brass Preparation
Before we go any further, size your brass with a full-length non-bushing die and trim to uniform length. Both these tasks are VERY important. If the brass is new, run it over the expander and trim to uniform length. While I don't like non-bushing dies for regular case sizing, this is where they are important. For neck-turning, you have to size the neck all the way to the shoulder junction and a bushing die always leaves about 0.050" unsized (by design, you can't fix that). If all you have are bushing dies, I recommend the Hornady New Dimension as your non-bushing die, they are well made and leave the brass very concentric.

Final Check
And here's the payoff, a perfect, 0.0125" thick neck. It's very uniform around the circumference, usually I only see 1 or 2 ten-thousandths variance which is perfect as far as we're concerned for this purpose. As a final bit of math (0.0125" x 2) + .308" = 0.333" so we calculate 0.007" clearance for a loaded round in our 0.340" chamber neck. Now, with the necks uniformed like this, we can select the bushing size that will give us our preferred neck tension and experiment with various levels of tension, secure in the knowledge that all of the cases will actually have the desired neck tension and thus give a meaningful result to our experimentation.

 

[spife7980]

They want you to size the neck down with a true full length sizing die to ensure that the expanding mandrel can work all the neck equally. A bushing die doesnt size the entire length of the neck. The bushing floats and so it will lift up a few thousandths when you size with it on top of having a chamfered edge that doesnt reach all the way to the bottom.

You want to squeeze it all down and then open it back up with the expander. The expander should provide us with a consistent internal diameter. Once we get the internal diameter consistent we can then turn off the discrepancies that are forced to the external side of the neck. Because the base of the neck isnt sized all the way down with a bushing die the internal diameter would be larger at the base and more material would be removed there relative to the rest of the neck. Since more material would be removed there from the external side it will create a ring of brass with a thinner thickness than the rest of the neck.

On top of that good turning practices also employee a slight cut into the shoulder of the brass with a cutter that matches the angle of the shoulder. This is done to eliminate the thicker shoulder brass from creating a bulge as it flows into the neck with repeated firing and sizings. If the neck isnt fully sized you wont get a precise cut into the shoulder.

Here you can see a bit of the neck that wasnt sized with a bushing die, it results in a more rounded transition from shoulder to neck in addition to the unsized portion.
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Now, after we have everything turned to a consistent diameter we want to avoid over working the brass on each firing/sizing cycle with excessive sizing down and then sizing back up. Because we know that the brass is a consistent thickness we could use a bushing die to size it down the exact right amount that we want and avoid using an expander at all as there should be no thickness discrepancies that the expander would be trying to push to the outside.

 

[grizzlestomp]

Very helpful. Thank you. So after using a FL die, then neck turning, I would then use a bushing die to achieve the desired neck tension?

 

[spife7980]

Very helpful. Thank you. So after using a FL die, then neck turning, I would then use a bushing die to achieve the desired neck tension?

Yes, you can. Or you can continue to use the traditional full length die if you wanted to. A traditional die is made to work with the largest variety of options, it will over work the maximum spec brass so that it can ensure that it is still capable of properly working the minimum spec brass. It can squeeze the neck down .010 below bullet diameter just to be sure that it gets it sized and then use the expander ball/mandrel to open it back up to only .002 below bullet diameter; that introduces an extra .008" of brass movement/working. The more you work the brass the quicker it will expire.

Some are honing their full length dies out to the exact diameter they want so as to eliminate that excessive .008" of brass movement (forster offers this option as well as whidden and any custom die makers). A bushing die performs this same concept but you can swap a bushing in and out where as once a traditional die is honed there is no uncutting that metal. If you have it honed out for thick brass and down the road switch to thin brass that missing material may be enough to not allow the die to properly size the brass. So most that hone it leave a couple extra thousandths and just mitigate some of the excessive sizing so that they only have .004" instead of .008". Its still excessive but not as dramatically.

A bushing will allow you to try a .289 bushing and then a .288 bushing and the go back up to a .289 if you wanted to do so. You can select which ever diameter you desire. And since its turned and the inconsistencies removed you can run the exact bushing you want with no worrying about expanding.

That said many are still running traditional unhoned dies with lots of success, myself included. Annealing will mitigate some of the stresses in the brass that occurs from the working.Steel can be heated/annealed to make it harder or softer depending on how its done. Brass will only get harder by working it and it will only get softer by heating it.