My 300 Win Mag cases are Federal Gold Medal. As near as I can tell it takes 88 grains of H110 (very fine ball powder for pistols) to fill a new case to the base of the neck. A once fired case will take 92 grains. My question is this: If with fired and then neck sized cases I find that my gun can handle 76.0 grains of H1000 behind the Sierra 220 MK then could I use that same charge in the smaller new case? The question really is which is the important perameter, case capacity or chamber capacity? Within reason of course. I would expect it to be different for a new 6mm Rem case fired in a 6mm Ackley chamber versus a fireformed case in that same chamber. But that is a much bigger % increase in case capacity. Thanks, Rufous.

Fired cases are tighter in the chamber than factory. That's why accuracy nuts with bolt action guns neck size only. They want the case to fit tight in the chamber. Factory ammo is designed to "feed" and fit a variety of chambers. Fire formed and neck sized is fitted to YOUR gun.

Particularly in a high end caliber like 300 Win mag, the brass will flow toward the neck. The neck will lengthen -- which is what neck trimming for length is all about.

Brass in the longer neck has to come from somewhere, mostly it's from the area just in front of the web. There are guages available for checking case thickness/thiness at the front of the web.

DON'T increase load beyond published spec just because the case holds more powder. Loading powder to case capacity works in black-powder cartridge rifles. You'll kill yourself loading to case capacity in a 300 Win mag. just because the brass/chamber accomodates more powder.

rufous

The way I understand it is that when the unfired brass is sujected to the same charge as the fired brass less pressure is generated. Something to do with the expanding brass causing the pressure spike to be delayed, which made the peak pressure to be lower than with fireformed brass.

It is the capacity of the chamber, not the capacity of the unfired brass, which determines the volume which contains the pressure of the powder gases. It is irrelavent what the shape or form of the thin brass in front of the head is to the final volume of the chamber, since on firing it will expand to match the chamber precisely.

In other words, using identical new brass with less internal capacity than fired brass will still result in the same, or very similar, pressure.

Shotshells, on the other hand, are a different story because (1) they operate at much lower pressures which may not obturate the shell completely in the chamber, and (2) more importantly, the resistance of the crimp to unfolding becomes less and less as a given shell is reloaded more times.

RUFOUS,
A fired case has expanded to fit the chamer of the rifle it was fired in. Depending on the size of the chamber, a case fired in one rifle may or maynot chamber in another rifle of the same make and calibre.
If a load is safe for your rifle it maybe used in new or fireformed cases. My chronograph tells me the same load in new brass will not give you the same velocities as it will in fireformed cases. Part of the energy is used in expanding the case. In my rifles this seems to reduce velocities between 25 and 50 fps. I hope that this is of some help.

------------------
BigBob

[This message has been edited by BigBob (edited 02-01-2002).]