School me on expander mandrels

[brushape]

What’s the deal with expander mandrels, when should I use them? Why and how?

Cartridge in question is a 7prc I already bought hornady bushing dies but got the wrong bushings. Using Peterson brass unfired


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[Taudisio]

The idea is to get consistent neck tension on the bullet. There are a lot of factors that can affect it, other steps you may already be doing have the potential to already give you consistent tension and it may just be redundant. Not knowing your entire setup, someone from the outside can’t tell you if it will help or not. Odds are that it will, hence why it gets suggested often.

 

[jhm2023]

I prefer removing the expander/decapping rod from sizing dies and then neck expand in a separate step using a mandrel sized to my preference of interference fit (neck tension). Plus, I feel that running something through the neck works better when pushing it through rather than pulling it through, but perhaps I'm crazy. Either way, I get considerably better SD and ES using a mandrel in a separate step.

 

[Lawnboi]

The premise is the same as the button that likely comes with your full length die.

Many just tailor a bushing and mandrel so that they minimally work the brass, versus a one size fits all die that likely squeezes the pissout of the neck and expands it back out.

I size/mandrel/decap in one step with a sac die. Being that they make a 7prc die, if you value consistency and your time that is the way to go imo.


I still keep a mandrel die around for odd calibers and virgin brass.

Zip a .002 under mandrel through that Peterson with some imperial on the rim, dry tumble it for an hour, and you will have nice even seating force on that first firing.

Don’t buy any of bushings till you figure out loaded neck diameter, if your going to use a mandrel size .004 under and mandrel up to .002 under. With spring back that gives nice consistent .0025 plus or minus interference fit. Atleast that’s what I do.

 

[CC11]

When I started reloading for my 28 Nosler I was having issues with the Nosler brass and my typical set up of sizing/depriming it. I could tell when I was seating bullets the necks were off as some bullets were harder to seat than others and knowing that would affect my groups. I went to ADG brass and run a mandrel through it now and my gun is a tack driver. Took all the questioning out of it for me and gave me peace of mind that at least that part of the puzzle wouldn't screw my shots.