Why do I need to flare case mouth (with photos)?

It’s often recommended to flare a case mouth, when reloading flat bottom bullets. Why? They go in just fine…

Using a boat tale type bullet:

The tale works in the same way as a shoehorn. It funnels the bullet into a case, when neck is under tension without shaving bullet material.

Using a flat bottom type bullet:

The bottom of the bullet doesn’t quite funnel itself in the case and forcing it down will remove (shave) some bullet material.

I am not going to go into different equipment and ‘the how’, this is something I am planning to cover later, but I will cover why…

Below are two pulled flat bottom powder coated bullets, that were seated and crimped. One was seated into a case that was flared, the other was ‘just’ seated without flaring (forced in). Bit obvious which one is which…

However, all damage is hidden inside the case, so it’s not very obvious that this has happened, unless you know what to look for.

There are a few implications to this:

  • Bullet is no longer the same weight. Depends on the neck tension, it can shave a lot or a little.
  • Bullet is no longer the same diameter when it engages the lands in the bore. So it’s reasonable to think that it will not generate the same pressure, velocity and may not have the same point of impact with the same tested charge.
  • Bullet is no longer powder coated, which will increase the chances of leading the bore.

Moral of the story, if you are using flat bottom bullets – flare the case mouth.

The base of the Flat bottom bullet can be slightly larger than the main bearing surface of the rest of the bullet. Hence the hidden damage.

With work hardened brass it can present depending on the seating depth that the bullet becomes loose in the case as well.

Your example is perhaps more extreme than a jacketed case but the same can happen. even on boat tails if the case has no chamfer.

No expert here. But I’d be surprised if that amount of damage would significantly effect accuracy. Let’s face it they get Jamed through the the rifling at speed, changing the same again.

Could be right, @Oldbloke. With cast projectiles, I am more concerned with leading than anything else. Accuracy is relevant, if all bullets are the same, then, maybe, POI will change, but not accuracy… However, gas cutting and leading is on the table (depends on velocity/charge of course). IMHO, best is just to follow all steps in loading cast, instead of taking shortcuts and paying for it later.

Agree, more you get right the better.
Just depends how OCD you are.