Forming 300 blackout shoulder problem

[760405reloader]

I think im just going to invest in the redding trim and form die

[dellet]

It might be helpful to know,

The make of the brass you’re trying to convert

Neck diameter

Neck thickness

[760405reloader]

Im mainly using lc,hornady, and aguila

[bangbangping]

Can you remove the decapper and look in the die? You should see a fairly sharp step where the shoulder is formed. I can't think of anything that would cause your results with multiple headstamps other than a bad die or a die packed with junk.

[cdl]

I normally use GSI International trim dies in my Dillon, but I have a set of Hornady dies in my go kit.

So out of curiosity I ran a few pieces of LC through, Chopping second, then used a 0.305" mandrel so they would fit on the trimmer pilot. Trim and deburr. I will still size and expand these again latter when I reload, but these are good enough for who it's for. Maybe yours will look better after you've run an expander through them.

[760405reloader]

Mine seem to look like that middle one even after expanding

[760405reloader]

I grinded down a shellholder and it seemed to make things better

[dellet]

Most likely the second trip trough the sizing die is just helping hard brass form.

The problem I see in your photo is the soft shoulder on the once fire 300 brass. If grinding down the shell holder helped this, there is possibly a die problem. Regardless, the shoulder on the converted brass should be much more defined than it is. By grinding the shell holder, you may create a headspace issue, or even start having misfires.

By measuring the neck and body above and below the shoulder will help to figure out if the die is sizing the brass correctly and just not forming the shoulder, or if the whole thing is off.

The body below the shoulder should be around 355”-.360”, the neck without the expander in will be around .315”-.320”. With the expander in the neck will be .325”-.330”.

If the neck and body diameter is correct, the shoulder should form correctly when fired.

Comparing yours to cdl’s, it looks like the Hornady die just really does not do a very good job of forming a shoulder.

[rlandry6]

The problem with grinding down the shell holder is that unless you are using a dedicated shell holder for this, any other tools, devices, or measurements that depend on the .125" measurement of the shell holder is going to be off. That's possibly creating multiple issues to resolve a single(hopefully) one.
I still believe the Sheridan slotted gauge will take you to your problem.

[rebel]

Though the Sheridan slotted gauge is a nice tool. It's not gonna help that shoulder at all rlandry,
If the brass chambers, fire form it and check the shoulder then. Should be sharp and defined. I like my forster sizing die. But the sharpest shoulders are produced by fire forming. You can use your die to the bump the shoulder back when reloading.
That die is suspect, I'd replace it.