Reply With QuoteI am far from an expert in case design, and I am not an engineer or a designer. If you was to break case design down into a science I would be the last person to ask about it. With that said I will tip toe lightly into the subject will my small amount of knowledge. I would refer you off to someone else like Chuck Hawk.
To start, with you have to figure primer usage, I have been told a small primer is good for a column of powder that would measure 1 and 1/2 inches. Flame travel of that primer is important. The size of the primer hole has something to do with this all. Accuracy gurus insist that a small primer with a small flash hole, makes the best ignition. Now I have tried to figure this out, I have talked to people, and with my own experiments I have not noted a difference in flash hole design, or primer size in accuracy. To be honest I don't have the time, equipment, or testing facility's, to prove this one way or another. I would say that the difference in flash hole design and primer size would differences is so subtile 95% of shooters could not notice the difference. To add to this different primers have different chartists, and this would throw another variable into the mix. For the most part I follow the leader, what a top notch shooter is doing, I will do. Case in point, with the 6PPC experts say never touch the flash holes, so I don't. Experts say use a fed match primer, I been told by a top shooter that there is not difference from a fed 205 and a 205M so I shoot the 205's. With a 6x47L I shoot Lapua brass necked down from 6.5x47 insted of 6XC brass because of the small primers. I use 450 CCI primers because that is what other use.
Projectile would be the next consideration, consideration one the different style and makes of bullets contributes to this. The 6mm bullet has a great BC, and it is one of the most common bullets made. It takes someone with out side the box thinking to change things, such as people like Randy Robbinnett. Randy in a partnership contributed to the designed of the 30BR. Randy sated making light weight 30 cal bullets, and I would say that this was the biggest contributing factor to the success of the round. Yes it is easy to neck of a cartridge but without the bullets it is pointless. Getting back to the point for accuracy the bullet makers have the biggest part to play in this. Case in point look at all the companies that make 64-68gr match grade bullets. (BIB, Bart's, Hotenstien,ETC) I would say 90% of these bullets will be shot in a 6PPC.
Looking at what works It seams that a short fat case works better than a long narrow case. With the case it has to have the right powder capacity, and fit with available powders. Many take the 220 case and blow it out to a shortened PPC case when shooting 22's. The PPC case has too much capacity for the light 22 rounds, so they shorten it up. Some would argue that the BR case has too much capacity for the light bullets, and this is why the PPC shines through. The PPC has a similar case capacity as the 222 rem, which has proved to work well with fast burning powders. The top shooting calibers have the case close to 100% full of powder.
With efficiency, well some cases work better than others. The size of the case has to do with pressure, and how the powder is burnt. Case in point in some cases a 6BR and a 243 Winchester have similar ballistic patterns, the 6BR does close to the same work as the 243 but it does it with less powder, it is more efficiently. There comes a end where the case is limited, and then wildcaters try to improve on this. The 6BR is a great case but it is at its end with heavy projectiles, this is why other try to get more case capacity by making it a dasher, a BRX, or whatever to solve the problem. The 6x47L has a thicker web and case head, and is able to withstand higher pressure than the BR case and it has bigger capacity to do this. The 6x47L case also has a rumored ignition problem, some stating that case is so big for the small primer, this is why some people use 6xc brass, or discredit the round. Some times the reason lies back to the firearm. But ultimately the round that is able to do the work with the lest amount of powder is preferred.
Shoulder angle has a part to play in cambering, and other things beyond my understanding. Sometimes shoulder angle is changed to gain case capacity, such as the Ackly Improved cartridges. I been told that shoulder angle also has a part to play in barrel life, with how long a throat last. The amount of powder burnt is ultimately the reason why barrels burn up.
In closing I would again state I am no expert and this field is beyond my understanding, but I saw no one else wanted to tackle the questions, so I thought I would give it a stab. Hopefully more experienced members will chime in.
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