Case Forming

Ambrose

This is an issue I've never heard addressed. If, for instance, I take a new .300 H&H case, load it with a near maximum powder charge for a 180 gr. bullet and fire it in my .300 Weatherby the case will form to the Weatherby chamber and some of the energy from the powder will have been used to thus form the case. Now if I take that same case that has been formed, load it with the same powder charge and bullet, and again fire it in my Weatherby, will the velocity be greater since energy from the powder is not now diverted to form the case?

zimmden

I don't see how it could be since the expanding gases exert the same pressure in all directions in the chamber and cannot go anywhere except down the barrel pushing the bullet. The same gas pressure that forms the new shoulder remains behind the bullet to accelerate it. The energy is not used up until the bullet is out of the barrel IMPO.

HandLoad

The amount of energy taken from the ballistics is so minor WRT the delivered energy of the explosion, it is nearly un-measureable.

HandLoad

Remember: every time you shoot, you take the brass past the elastic limit. Thus it is deformed by a regular shot. The only variance between the "Normal" Obturation and "Fire-Forming" is the amount of deformation that occurs beyond the elastic limit of the brass. Further, if it is past the elastic limit at the smaller dimensions, as it expands the brass offers less and less resistance.

nononsense

Ambrose,

"Now if I take that same case that has been formed, load it with the same powder charge and bullet, and again fire it in my Weatherby, will the velocity be greater since energy from the powder is not now diverted to form the case?"

The simple answer is that with the same charge used in the fireforming, the pressure will be the same and in essence lower since now the case capacity is larger.

Your near maximum charge in the smaller parent case becomes a smaller charge and lower pressure in the new larger capacity case.

Best.