Bullet seating issues with 375-338

[spencerhenry]

Got the rifle rebored a few weeks ago. Just got the dies today. Resized 55 338 win mag cases through the 375-338 Redding dies. Cases look good, no issues expanding necks. But, when I tried to seat bullets, they are VERY tight. The first one was tight, and did not seat. I chamfered the neck and tried again and it worked but still tight, the next one after chamfering crushed the shoulder. That was with nickel brass, then I tried regular brass with a chamfer and that was better but still shaving a tiny bit of jacket and seating pressure is high.
This is used brass, most of the primer pockets looked like once fired, but some is probably twice fired.
Should I see if Redding makes a slightly bigger expander button? or Perhaps get an 'M' die. I do intend to load cast bullets in this round, starting bullet size will be .379. Groove size is supposed to be .376, so I might need to drop down to a .378 or even .377. But, if I can't seat a .375 to .376 jacketed bullet, an oversize cast bullet is going to be worse.

I am only using the nickel brass because I have it, I prefer non-plated.

Suggestions?

 

[spencerhenry]

Expander is .373 by my starret calipers.
I wonder if resizing necks and use brass has made for hardened brass that is springing back to being undersized and annealing would solve the issue? Bummer that I already primed them all.

 

[spencerhenry]

Initial load testing is pretty good. A 235gr speer with 70gr of 4064 runs 2800fps with no pressure signs.

Some the fired brass has tiny cracks in the neck, looks like I will anneal the next batch.

 

[LA50SHOOTER]

Got the rifle rebored a few weeks ago. Just got the dies today. Resized 55 338 win mag cases through the 375-338 Redding dies. Cases look good, no issues expanding necks. But, when I tried to seat bullets, they are VERY tight. The first one was tight, and did not seat. I chamfered the neck and tried again and it worked but still tight, the next one after chamfering crushed the shoulder. That was with nickel brass, then I tried regular brass with a chamfer and that was better but still shaving a tiny bit of jacket and seating pressure is high.
This is used brass, most of the primer pockets looked like once fired, but some is probably twice fired.
Should I see if Redding makes a slightly bigger expander button? or Perhaps get an 'M' die. I do intend to load cast bullets in this round, starting bullet size will be .379. Groove size is supposed to be .376, so I might need to drop down to a .378 or even .377. But, if I can't seat a .375 to .376 jacketed bullet, an oversize cast bullet is going to be worse.

I am only using the nickel brass because I have it, I prefer non-plated.

Suggestions?

One recommendation that you may want to consider is using a 375 cal. expander mandrel, especially if your encountering a lot of spring back.
Sinclair or Brownell's has them and the die (2 sizes available - either a 7/8 x 14 for standard presses or a 1 1/2 x 12 for the big presses).
You could choose between either an expander or a turning mandrel as there is 0.001 difference in size. - That may get your necks to where your not encountering that large amount of neck tension and usually running the necks across a mandrel doesn't hurt your run-out.

- Ron -

 

[JRS]

Initial load testing is pretty good. A 235gr speer with 70gr of 4064 runs 2800fps with no pressure signs.

Some the fired brass has tiny cracks in the neck, looks like I will anneal the next batch.

The plating on that brass is pretty hard as it is. Annealing nickel plated brass will make it even harder.