This brass is brand new, does it have to be sized and belled before loading ?

I always do, but then all I have to do is put it in the Dillon as usual.

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Science plus Art

I'd check a few random cases to see if they chamber easily and, if they do, they have probably been sized at the factory.

I have never sized new handgun brass, of any caliber, and have never had a problem.

With a Dillon (or perhaps even ANY progressive press) you can leave out various dies as desired. You could adjust station 2 beller/powder drop, to not do any belling if you wanted.

In such as Dillon 550/650, all of that is part of the "one lever pull, one loaded round" process anyway, so you wouldn't gain any time advantage by leaving them out.

Personally I never found the need to trim to length any pistol brass either.

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Dum vivimus Vivamas

I say do it ------new brass out of the bag is not all uniform....****nning it through your sizer will make them all alot closer to the same size and uniform for you to have the most accurate ammo from your loader

I would do it and leave the depriming pin in as I have found a very few new cases with no primer hole.

If I were loading it I would send it through the progressive press as usual.

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Freedom is never free!!
SWCA #3437

Last weekend I finished up on prepping 1000 new Starline 357 Magnum cases.

If you measure your brand new brass you will likely find that it is sized nearly exactly to the SAAMI mean diameter. In the case of my RCBS sizing die that is 0.002 inches larger than my sized cases.

So, I would assume that NOT sizing the brass will result in less Neck Tension than what would be seen in sized cases. That might create issues with Bullet Pull in some revolvers using a full power load of 357 Magnum. In a 38 special it likely won't be a problem as long as the ammunition is properly crimped. BTW I would NEVER go without sizing any Semi Auto ammunition, the loss of Neck Tension could lead to a bullet setting back to a hazardous length while the round was being chambered. Being a bit OCD and rather fond of consistent procedures I ALWAYS size any new cases.

As for flaring the cases, I have never in my entire life ever seen any new brass that was factory flared. Lessons learned the hard way have taught me that simply chamfering the ID of the case will NOT prevent a lead bullet from being destroyed by simply pressing it into the case. In fact I was also in a position where I actually considered making a miniature coffin for the 357 Magnum case that was destroyed in this lesson. Yeah, I do mourn every 357 Magnum case lost, because they have been darned difficult to acquire. Needless to say I now ALWAYS flare all of my handgun cases.

So, my short answer is that you do need to size and flare every single one of those new cases. While you are doing it just be glad you aren't a bit OCD. Because if you were a new batch of cases would also mean trimming every one to length and reaming every flash hole to 0.082 inch.

I would rezize them. You do every other time they are loaded, yes?. You could probablu get by with out but why not.

As to flairing or belling yes to that also if you want to start the bullet for seating.

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Still Running Against the Wind