One could spend quite a bit of space addressing your questions, but we will try to summarize.
The primary factor in design pressure is the chamber of the firearm. Within a given chamber design, the case is usually the weak point in the system. But there are exceptions to both of these generalizations.
The chamber shape has an effect, as in the .45 auto where the feed ramp leaves a part of the case unsupported by the chamber, so that the case must bear the entire load at that point.
The thickness of the chamber and the material determine the strength of the chamber. For instance, a Ruger Blackhawk in .45 Colt will withstand a lot more pressure than a modern Colt revolver, which, in turn, can withstand more pressure than a 100-year-old Colt revolver.
The action type has an effect also. A bolt action is inherently stronger than a lever action, for instance, though improvements in design can reduce the difference.
In the past, different case designs had an effect on the pressure a cartridge could stand, but modern cases are more or less equally capable for their design cartridge. However, cases for one cartridge may be considerably thicker than for another cartridge, and therefore capable of withstanding higher pressure. The design pressure of the 300 Winchester Magnum, for instance, is considerably higher than some apparently similar cartridges.
In earlier days, a countersunk revolver chamber could withstand higher pressure than a non-countersunk chamber, but modern cases have made this distinction obsolete.
As mentioned earlier, this is a complicated subject, and an overview may not be very helpful. Suffice it to say that there are people who load cartridges well beyond design limits. Some of those experiments have led to changes in specifications for cartridges, where the cartridge had more capability than had traditionally been recognized. Other of those experiments led to missing fingers and worse.
The issue is much too complex for there to be charts or formulas relating charges and seating depths to pressure. Sometimes changes have a linear effect, and sometimes they are dramatically nonlinear. Some powders, for instance, burn faster as pressure increases, which makes for some startling pressure increases with relatively small powder increases.
At the other extreme, it has finally been proven that an overbore rifle cartridge, in a barrel with throat erosion, loaded with a much reduced charge of slow burning powder can detonate and demolish the firearm. Contrary to misinformed opinion, this does not happen in pistol cartridges.
All these complicated factors indicate why it is so important to follow loads developed in laboratories and published in reliable manuals rather than striking out on one's own.
Unless one has a PHD in metallurgy and a laboratory at hand, it is best to stick with published design pressures.
[This message has been edited by KLN (edited 11-20-2001).]
The primary factor in design pressure is the chamber of the firearm. Within a given chamber design, the case is usually the weak point in the system. But there are exceptions to both of these generalizations.
The chamber shape has an effect, as in the .45 auto where the feed ramp leaves a part of the case unsupported by the chamber, so that the case must bear the entire load at that point.
The thickness of the chamber and the material determine the strength of the chamber. For instance, a Ruger Blackhawk in .45 Colt will withstand a lot more pressure than a modern Colt revolver, which, in turn, can withstand more pressure than a 100-year-old Colt revolver.
The action type has an effect also. A bolt action is inherently stronger than a lever action, for instance, though improvements in design can reduce the difference.
In the past, different case designs had an effect on the pressure a cartridge could stand, but modern cases are more or less equally capable for their design cartridge. However, cases for one cartridge may be considerably thicker than for another cartridge, and therefore capable of withstanding higher pressure. The design pressure of the 300 Winchester Magnum, for instance, is considerably higher than some apparently similar cartridges.
In earlier days, a countersunk revolver chamber could withstand higher pressure than a non-countersunk chamber, but modern cases have made this distinction obsolete.
As mentioned earlier, this is a complicated subject, and an overview may not be very helpful. Suffice it to say that there are people who load cartridges well beyond design limits. Some of those experiments have led to changes in specifications for cartridges, where the cartridge had more capability than had traditionally been recognized. Other of those experiments led to missing fingers and worse.
The issue is much too complex for there to be charts or formulas relating charges and seating depths to pressure. Sometimes changes have a linear effect, and sometimes they are dramatically nonlinear. Some powders, for instance, burn faster as pressure increases, which makes for some startling pressure increases with relatively small powder increases.
At the other extreme, it has finally been proven that an overbore rifle cartridge, in a barrel with throat erosion, loaded with a much reduced charge of slow burning powder can detonate and demolish the firearm. Contrary to misinformed opinion, this does not happen in pistol cartridges.
All these complicated factors indicate why it is so important to follow loads developed in laboratories and published in reliable manuals rather than striking out on one's own.
Unless one has a PHD in metallurgy and a laboratory at hand, it is best to stick with published design pressures.
[This message has been edited by KLN (edited 11-20-2001).]
