selecting 6mm neck bushing and mandrel combinition

[dixiecricket]

Im loading 6GT and am changing up how I do things and want to try a neck mandrel after full length sizing in a Whidden bushing die. Here is where I am:

1. My chamber neck is .273" based on the reamer print and verified by a cerrosafe casting.
2. My Alpha 6GT neck wall thickness is 0.0145-0.0150", leaving a 0.001" clearance, not enough for field type shooting I do. It was causing problems.
3. I lathe turned necks to 0.012"
4. Changing from Hornady dies (my set doesnt size the base nearly enough) to Whidden bushing die.
5. I have a separate chamber gage cut with the same reamer. I expect loaded rounds to drop freely into and out of the gage. I cannot have a stuck case causing me to drop points in a timed stage.
6. I'm loading in a Dillon 650 with chargemaster . Its the only way I can keep up with loading ammo.


Here is what I need help with:
1. If I want to have 0.002" neck tension, is a .264" neck bushing going to be right?
2. What diameter and brand of neck mandrel should I run after full length sizing?
3. How much should the mandel expand the neck back up? should I use a neck bushing to create 0.003" neck tension, then expand it back out on the mandrel by 0.001"?



If this is all hashed out somewhere else, please point me in the right direction

Thanks,
Marshall

 

[savageshooter86]

Curious to hear answers on this one. My understanding is the mandrel is the amount of tension in this situation. So a 242 mandrel would be roughly 1k tension. A 241 would 2k. And 240 mandrel 3k? Assuming your annealing and the amount of spring back. So the busing selection would be whatever feel You want expanding and least amount of working the necks

 

[Richard Coody]

Just remember when you size with a bushing brass springback goes one way and when you expand with a mandrel brass springback goes.the other way.

Personally I like to use a non bushing full length sizing die when using mandrels for final sizing. I use the k&m kit with mandrel sizes in 0.0005 increments. Experiment to see what neck tension that combination likes. An arbor press with seating force gauge will help you develop brass prep techniques for consistent neck tension. Without consistent neck tension you will never reach the combinations potential.

 

[dixiecricket]

Honestly, if I have to use an arbor press then I'll scrap this route. I've seen this method mentioned as part of reloading match ammo on a Dillon.

 

[dgeesaman]

I see no reason you’d need an arbor press.

When sizing a 6mm neck down, on not-hardened brass, I get about .0005” spring back on both the sizing and expanding step. I like to have the inside of my sized brass at around .240 / .2405 before I use a .2415” expander to attain .241” ID which is just a little more than .002” neck tension. I’d rather not hazard a guess at your ideal bushing diameter but based on the above you should be able to judge that well. Just take care that most neck bushings can be off on size by .0005” high or low. If you want neck bushings that are dead perfect, get benchrite carbide bushings.