Working up a load for the 22-6MM and everything was fine until this morning
Shot a five shot group that was decent
Went to load 5 more and started crushing cases to a mushroom at the shoulder
I haven’t changed anything from the last time which was yesterday
All cases were sized and primed at the same time so there nothing different about them
Took the die apart and cleaned and everything is moving smoothly
What has happened ?

Is the expander ball too close to the neck sizing area of the die. Forster dies are designed to have them expander ball right under the neck but if they ball is too high at will crush the cases.

This is happening when I’m pressing the bullet in
I had already pressed around 25 in with no problem and this just started

Get your micrometer or calipers and a strong light and recheck before you crush another case. Wes is correct about Forster dies. If it were only one I could blame Murphy but 5 somethings off kilter somewhere. Same brass lot? If so you could have 'soft' brass.

Same brass lot
Same everything
I just loaded the remaining 4 of 50 pieces
I ruined 10 pieces
I did chamfer them deeper inside and outside
Bullet pressed in perfectly
These are Hornady dies
Very limited choice when it comes to this particular cartridge

RCBS seating die? These dies are designed to crimp or not crimp depending on how you set up the die.

Have you trimmed all of the cases to the same length? If these cases are longer and you didn't set up your die properly it may be trying to crimp the case on the bullet. But if there is no cannelure to crimp in it may crush the neck into the shoulder.

Just trying to guess at the issue.

These are Hornady dies
I prepped all cases at the same time and they are all the same length
The seater die is set up per spec’s
I’ve been doing this more than 20 years and have never encountered a problem even remotely close to this
To load and fire as many as I have since Friday morning and this happens with the same set up is just plain weird
May be something to with being 6MM cases necked down to .224 but what I can’t find especially since they all mic the same and most all have loaded perfectly

I'll go out on a limb have you measured the thickness of the walls at the case mouth

Yes I’ve mic’d everything
Right now I’m leaning towards the inside chamfer not being deep enough and the bullet pushing the case neck down into the shoulder
I will say the bullet was pressed in each case that mushroomed
I’m thinking it was just too tight to start seating the bullet and it crushed the case
Since I’ve chamfered the inside a little deeper I’ve loaded 6 more with no problems

I'm sticking with my bad brass guess. I've loaded for 40 years and never has that happened. When the cases were made I'd bet the shoulders weren't properly formed and got brittle. Has some Winchester 30/30 brass you could only use Ball or Spherical powder otherwise the mouth would twist&turn goofy upon clambering. 30/30 brass ain't the strongest design so I chucked it up to the same thing this is Just one them things.

Very possible but could that be possible when they all came out of the same bag ?
I’ve never been stumped with a reloading issue until now and all I have is guesses

Did you anneal the cases? When forming brass to a different caliber it's a good idea to anneal them.

This is new brass
The only thing I’ve done to it is size trim prime

The bullets are 75 grain eldm

No issues with any of the brass I’ve already fired so I’ll just chalk it up to bad brass or n that lot

I had something similar happen several months ago. I just happened to take a pipe cleaner and just touch a bit of lube in the case mouth and they straightened back up. I could feel it when it was going to happen. It didn't happen on the second round of loading at all.

What brand of brass? Could have been over-annealed from the factory and is too soft.

You need to lube the bullet. You can do that, or tumble your brass about 15 minutes in corn cob and the dust will serve as lube.

Bullet lube is pretty easy. Graphite powder works but is messy. I put bullets in a ziploc, spray some Hornady one shot case lube in the bag and then work the bullets around. Then load.

This has happened to me many times with super clean brass.

It sounds like you have too much neck tension. Is the neck diameter stamped on your barrel? If it is a no turn, you still may need to use a neck turner. I would adjust it just enuff to just clean up the neck about 3/4 way around. Make sure your turner has the angle of your shoulder and cut just deep enuff to just kiss the shoulder. If a bullet wont start into a fired case, that means the outside diameter of the neck of the fired round is too thick for your chamber. and you need to neck turn. The reason it does it on the 2nd firing is that brass flows just a tiny bit. Also make sure that you trim to length

You might want to push an empty case without bullet up into your seating die to make sure there is no resistance. It sure sounds like the neck walls are too thick on some of your brass. There are variations in the best of brass. If the walls are too thick, then neck turning is your answer. another thing to try is to raise your die a 1/16" and lower your bullet seating stem to compensate, Let us know when you get it worked out.

Sounds like different brass thickness on neck. Mixed brands?? Inside neck reaming needed?