6 UM or 6-7PRC?

[huntnful]

Got my 6-7prc out on the range this morning. Loaded up 65grns n570 with 115 dtacs. Seems like the rifle is going to be a shooter. First 3 shots out of the gun with a 3/4” dot for reference. Velocity was 3130 average over 8 shots this morning. Going to run the velocity up once all my brass is fire formed. Only crappy part is I collapsed 2 shoulders out of 10 when I was seating bullets. Hopefully that trend doesn’t continue. UM did a good job on the build.

Open up those necks with a bigger mandrel if you're collapsing the shoulder by just seating bullets. That's way too much seating pressure for sure. Or get the right bushings that don't size down the neck as much when you're taking the 7mm necks to 6mm.

 

[longrange13]

Open up those necks with a bigger mandrel if you're collapsing the shoulder by just seating bullets. That's way too much seating pressure for sure. Or get the right bushings that don't size down the neck as much when you're taking the 7mm necks to 6mm.

I’ve got the bushing that’s .003 smaller than loaded neck size and then I’m using the Sinclair carbide mandrel. I’ve always had good luck with this combo, but there is a good bit of seating force. Have you had good luck with any other mandrels? I’ve used some other brands before but since they aren’t carbide they end up gauling necks and end up being a pain.

 

[huntnful]

I’ve got the bushing that’s .003 smaller than loaded neck size and then I’m using the Sinclair carbide mandrel. I’ve always had good luck with this combo, but there is a good bit of seating force. Have you had good luck with any other mandrels? I’ve used some other brands before but since they aren’t carbide they end up gauling necks and end up being a pain.

Brushing the inside of the necks with an oversized nylon brush on a drill bit helps significantly with seating pressures.

As well as 21st century moly inside the necks.

What size mandrel are you using?

 

[longrange13]

Brushing the inside of the necks with an oversized nylon brush on a drill bit helps significantly with seating pressures.

As well as 21st century moly inside the necks.

What size mandrel are you using?

I’ll give that a try, thanks. It’s a .242” mandrel

 

[huntnful]

I’ll give that a try, thanks. It’s a .242” mandrel

Definitely brush the necks. And I would moly them also. But I bet just brushing them solves it. Virgin necks on brass can be super sticky, until you get them once fired and put a layer of carbon inside there.

 

[Ryan Avery]

For some reason this neck down is PIA. Compared to others I have done. We lost a few soldiers when I necked down 150 cases.

 

[Ryan Avery]

@Ryan Avery got mine in from UM this week, they did a great job. What was your coal with the 115 dtacs? Going to load some test loads tonight.

BTO is 3.19, thats all I have on my Phone. I will post my notes when I get to the shop.

 

[Axlrod]

Do you run into problems using Imperial Sizing wax? With deadening powder or just getting powder into the case.

I use dry moly on the inside of my necks.

I put it on the bullet, so no powder issues. Very little to none of the wax can touch the powder. I haven't observed any problems. I have used moly as well, the wax works better for this application.

 

[khuber84]

You're necking down 0.041 that's a bit. Work hardens the brass. After you neck down all the way, I'd anneal before mandrel, then seat bullets.

 

[Axlrod]

Thanks for the info. Any idea how low I could go on powder charge and still get a decent fire form? I’d like to take it easy on the barrel if I can for the first 100 rounds.

It would be really hard to quantify barrel life vs. a few grains less powder. To get your brass completely fireformed will typically take 3 fireings or so. I like FF loads to be around 90% of max. New ADG brass fired in my 30 Nosler doesn't need the shoulder moved back, until after the 3rd time. Things are much more consistent after the first time however.

 

[longrange13]

It would be really hard to quantify barrel life vs. a few grains less powder. To get your brass completely fireformed will typically take 3 fireings or so. I like FF loads to be around 90% of max. New ADG brass fired in my 30 Nosler doesn't need the shoulder moved back, until after the 3rd time. Things are much more consistent after the first time however.

Cool, thanks for the info. I’ll just keep rolling with 65 grains then and bump up after the first firing.

 

[longrange13]

You're necking down 0.041 that's a bit. Work hardens the brass. After you neck down all the way, I'd anneal before mandrel, then seat bullets.

I was wondering this same thing. If it was better to have a softer shoulder or harder shoulder to prevent buckling. I’ll run them through my amp and see if it’s better.

 

[Ryan Avery]

You're necking down 0.041 that's a bit. Work hardens the brass. After you neck down all the way, I'd anneal before mandrel, then seat bullets.

This made no difference IME.


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[khuber84]

This made no difference IME.


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I've only necked down from 30 to 7mm, 7mm to 257, 6.5 to 6mm, and 6mm to 22. Always did it in 2 steps with a bushing die, or with a Hornady universal neck die.

I don't recall every crushing a shoulder seating bullets. Imperial dry graphite lube, ensuring you're using a seating mandrel prior to seating, and annealing the neck has always given me success.

I'd think the best die to execute this big a job properly would be the SAC 7prc die with a variation of neck/shoulder inserts.

I wonder if an inside donut is being formed, and seating the bullet to hit the thicker donut area is causing the shoulder to collapse. I always try to be seating above the neck shoulder junction, especially on necked down wildcats, that brass you squeezed down has to flow somewhere.