Reeder Custom Guns - Forming .310GNR brass question

I’m starting to load some .310’s and looking to see what you guys all do to bring down the neck of the .405 brass without crushing them. I have a 378 GNR set, so that’s the first step down. I did a couple to .310 next and it is a long size down from .378. Even we’ll lubed brass I boggered up 2/6, so I stopped. Already talking to a couple people that say just neck size only till you fire form. could you use maybe a .357 pistol die to help in between the .378 and .310? I’m practicing on .405 brass before I try my limited supply of .310 brass. Thanks for any advice, Michael

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405 down to 375, then down to 358 or 338 at the lowest, then down to 308. The 357 Mag die won't work as the 405 case won't go into the 357 die. Neck sizing then fireforming is fine, but you still have to go down to .308 before you can fireform, so going in steps is the only way you can do it.

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since the .405 is smaller in diameter than .308/.30-06. Something like a .358 Winchester or .35 Whelen, even a .338 Win. sizer would step down fine. I could tell you some of the nutty stuff I do but I'd certainly not want folks to try them on their own. Whatever works and gets it done.

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Forming .310GNR brass question

you need to go down in a couple of steps.

If you have a .35 Remington it migh be close