The Accurate Reloading Forums THE ACCURATE RELOADING.COM FORUMS Guns, Politics, Gunsmithing & Reloading Reloading Accuracy and case designGo | New | Find | Notify | Tools | Reply | |
| Accuracy and case design | Login/Join |
One of Us |
If I saw it once Ive read it a dozen times that case design has nothing to do with accuracy. For those who claim so I have a question. How do you explain "inherint accuracy" in cartridges like the 308, 6.5X55, 223. ppc and so on?? Inquiring minds want to know.. | ||
|
one of us |
It's just a matter of how you define accuracy. For hunting rifles for normal hunting scenarios, it doesn't matter. The stocks, barrels, firing positions, wind, bullet quality, all induce larger variations than the cartridge itself. For extreme long range, it matters, primarily from a velocity variation perspective. Short powder columns and sharp shoulders help. When you start shooting 16 lb rifles off the bench with match grade components, things show up that otherwise don't. For extreme accuracy (100 yard benchrest, etc), it matters. Even there, people argue about it, and they are discussing differences as small as .05" groups. JMO, Dutch. | |||
|
| one of us |
Harold Vaughn develops an interesting idea in his book, and shows data to support it. As the bullet starts to move down the barrel, external recoil begins. As the barrel tries to slide back in the stock, the barrel lug presses against the stock, which then starts to push the tip of the barrel upward. This is the source of much of the barrel vibration. Long actions have a bigger open place than short actions do. So short actions are more rigid, and produce less barrel vibration. Short cartridges are therefore supposed to be more accurate than long ones. It's in a book, so it couldn't be wrong, could it? Anyway, that might help explain why the 6ppc is such a good cartridge, and why benchrest shooters favor the 308 over the 30-06. Personally, I am unburdened by any direct knowledge of the subject. | |||
|
| one of us |
I have read Vaughns book several times (the best gun book ever writen) and I can't recall one word on action length. Dutch is right on with his answer. Good Luck! | |||
|
one of us |
Quote: Well said. I, too, share this shortcoming (thankfully).  RSY | |||
|
| One of Us |
Quote: Inherint accuracy.. Im not suggesting that any given cartridge cannot be made to compete with others commonly used for extreme accuracy through extensive gunsmithing. Im talking about the fact that a certian handfull of cartridges (like my list above) chambered in any given factory model will predictably produce better groups than many of those that do not make the list. Of corse there are always exceptions and many other factors in accuracy, but more often than not factory hunting rifles chambered for a few cases will have a distintive edge before they ever come out of the box. Thats what Im talking about and I believe it to be true, which to me dispells the myth that case design is irrelevant to accuracy. I believe it is relevant. | |||
|
| one of us |
Irv... I wholeheartedly agree that Harold's book is a great one. He does thoroughly develop the idea of the moment produced by the forward force of the stock on the recoil lug being a major source of barrel vibration. Perhaps I didn't make the transition to my own thoughts perfectly transparent. The statement about short actions being more rigid is my own. If the action is more rigid, the upward deflection of the barrel tip will be less. Sadly, Harold isn't with us anymore. I'd really like to know more about some of his experiments. It's a real loss. Anybody that will instrument rifles the way he did, and lug an old Tek 555 tube type oscilloscope around, with a gas generator to power it, is a hard-core experimenter. | |||
|
| one of us |
denton; Sorry to hear about Harold. I had heard that he wasn't doing well. When I bought his book I was so thrilled with it that I phoned him. Glad that I did he was quite a gentleman. What thrilled me was the first logical explaination of wind drift. Very few gun writers have the technical background, but many pretend they do. Take Care! | |||
|
| one of us |
Quote:Quote: Hey Wstrnhuntr, I completely agree with you and Dutch. Perhaps we are dating ourselves a bit to recognize the distinctions as clearly. 20-25 years ago, few folks would even give your list a second thought and agree readily. Go back another 25 and only a fool would argue the point. Back then, the Bullets we had just weren't as well made as the ones we have today. 22cal and 30cal dominated. That is where the efforts were focused to make those Bullets as close to perfect as possible. As improvements were made to the manufacturing techniques, they were also incorporated in the other calibers by Sierra and Nosler. Everyone else had to respond to their lead in order to retain market share. Somewhat the same with Powders, but the big difference is not as clear for an individual Powder. What we can easily see though is a much larger variety of Powders that will work with each cartridge. This allows a better opportunity to locate a combination that just matches the rifle/cartridge combination. But there is more to the Powder portion of your question than is readily apparent. For some reason, when you take a 222Rem/223Rem or a 308Win, you will normally find that 4-10 Powders may all work very well. And 2-5 may be darn near tied for accuracy potential. On the other hand, something like a 22Hornet or a 7mmRemMag(one of my favorites) has a much narrower group of Powders that will get both excellent Accuracy and excellent Velocity. If you have a few Load Manuals, it is fairly easy to see which calibers seem to match well with a larger number of Powders. Good topic. | |||
|
| one of us |
Westernhunter, Problem with "inherent accuracy" is that it is not defined. In general, you find some correlations. For example, in 308 caliber, the 308 Win is ususally more accurate than the 300 WBY. Is this because the 308 win is inherently more accurate? Or is it because the 308Win's muzzle pressure is half that of the 300WBY, and thus crown imperfections become more evident in the WBY cartridge? Or, is it because the 308Win is ususally shot from a 20" to 22" barrel, and the 300WBY from a 24 or 26" barrel". Longer barrel, more barrel whip. Or, is it because the recoil from the 308Win is less than the 300 WBY, making shooting it off the bench consitently more difficult? Und so weiter, etc, etc. Teasing out the true causes of accuracy requires isolation of factors like the ones mentioned, and then the instrumentation and dedication to quantify them. FWIW, Dutch. | |||
|
| one of us |
Boy oh boy, this is the first place I've seen this discussion where there were so many disbelievers.  I would also be in that camp.Vaughn's work is a classic and I never doubted that he was too. I recall the central theme of his treatment on the subject dealt with attendant reductions of bolt thrust with smaller cartridges and other advantages that accrue lessor case capacity in regards to barrel/action stress and movement under strain. The list of things necessary to generate accuracy and precision is longer than my arm. While case design may have SMALL influence on internal ballistics, it will NOT generate accuracy when other fundamentals are ignored. What some cases may have is a very fortuitous blend of capacity, that when blended with proper powder and primer, create a lovely harmony, and perhaps that allows minor oversite elsewhere without great penalty. It is interesting to note that most NBRSA 5 shot records at present were established before the PPC cartridges came to the fore. So, I'm left to wonder, what the hell is everyone talking about when they discuss "INHERENT ACCURACY"? I've looked for technical information related to internal ballistics that would support the theory, but find none. Accuracy is the product of many things properly assembled and executed, not voodoo. For those that prefer the later, I've a barrel of hydrostatic shock in the garage I'd like to sell you.  | |||
|
| one of us |
Hot Core, Dutch: I'd like to comment on this thread. I agree with you guys. After a lifetime of rifles and ten years of shooting benchrest and hanging out in a rifleshop with a bunch of Hunter class benchrest guys, I've devoloped some opinions. Those cartridges on the list do work. I've come to the conclusion that assuming a correctly built rifle that the 222, the 6PPC, and the 308 are probably about the right size in case capacity for the bore size. The companies that make bullets and bullet jackets have probably concentrated their efforts on these sizes since they are shot most in competetion hence the best quality in bullets. Then its necessary to find a bullet weight that will balance out with the case cpacity and bore size. In the 22 its from 50 to 55, in 6mm it seemed to be 60 to 70 gr. and in the 308 it seemed to be 155 to 170. Then it is necessary to find a powder that burned well in that size case and bore size. Also, the same as the quality of bullet jackets the quality of brass assumes a great importance in the quest for accuracy. We always felt that one of the secrets of the PPC's success was the high quality of the original Sako 220 Russian brass. I shot the Varmint classes with PPC's but I watched my Hunter class friends work on a ton of wildcats. They were mandated by the rules to a minimum case of 45 gr of water or about 30-30 size. One of the extreme experiments was an attempt to duplicate the design of the PPC in a larger case. I watched those guys develop the 6mmFireplug. That was a 45-70 taken down and shortened to 6mm with a 30d shoulder. Randy won the Pa Hunter Ch, back in the 80's but the cartridge wasn't as consistent as he wanted. The 308 worked but was hard to manage recoil wise with 168 gr bullets. That led to light weight bullets but the accuracy wasn't there. Eventually those guys settled on an improved version of the 30-30 with bullets in the 130 gr range. The quest for a powder went on and on. The old AA2015 from around 1990 worked great but supplies played out and T32 worked but again suppies played out. But, once they found a powder that came into balance with the case capacity, bore capacity and bullet weight the rifles started to shoot. Today, the 30 Aardvark(basically the 30-30 Imp.) rules Hunter Benchrest here in the N.E. at least. The case is long and slim as opposed to the short fat PPC in the VArmint classes. We concluded from all this that it wasn't the shape of the case that made once cartridge more accurate but rather the ability to bring all the components into a balance with the bore size. And that just made the harmonics of the rifle easer to tune. Personally, I've never been sure our conclusions were scientific but that was our experience. I think that those cases that just seem to work accuracy wise were those that started out about the right size, were shot with the right weight bullets right away, and were in bore sizes where good bullets were avaiable. knobmtn | |||
|
| One of Us |
Quote: Knobmtn, Thanks for the input, I think you've hit the nail on the head. Ackley used to refer to that as "proper adjustment between case capacity and bore size". But I think that it goes even deeper than that. An effecient and consistant discharge is in essence what we are talking about and the variables involved in obtaining that are great. Clearly there is no distint shape that all of the cartridges on "the list" share. I believe that the success of the PPC's can be attributed more to this ballance of internal ballistics than short and fat. But by the same token, the design of the case DOES have an influence on internal ballistics. To believe otherwise denies the fact that a handfull of cases have a greater tendancy to accuracy than others. Considering that the gasses must make their way past the shoulder of the case, I dont see how doing so efficently could not be a factor. This may be a bad example, but kind of like the difference between a stock and a performance exhaust system on an auto. Minute as it may be, there is going to be a difference in the flow dynamics there with varying shapes and components. At least thats my theory. | |||
|
| one of us |
wstrnhuntr: Quote: "An effecient and consistant discharge is in essence what we are talking about and the variables involved in obtaining that are great" I would say you and I are defintely on the same wave length regarding accuracy. Quote: ". Ackley used to refer to that as "proper adjustment between case capacity and bore size". The guys that I've been involved with are mostly in their mid 50's today. We grew up regarding Mr. Ackley as the ultimate authority on this stuff. We're all lifelong rifle and accuracy enthusiasts. My friends really shoot the Hunter class, I think, because it is a good place to test wildcats in meaningful way. Along that kind of road one develops some opinions and learns a little. knobmtn | |||
|
| one of us |
Hey knobmtn, Excellent post. There is a lot to be said for being able to "learn" from others by reading a book. Eliminates a lot of re-inventing the wheel. But, it is possible to be mislead into improper conclusions and never be aware of it without a certain amount of first-hand experience to compliment and support(or disprove) that book knowledge. Quote: ... Quote: Can't remember who/where it was that I became enlightened to "a Balanced Cartridge Design". But over the years, I've come to believe it does exist for the components we have available. I can see where both of you are going with: Knobmtn: "it wasn't the shape of the case that made once cartridge more accurate but rather the ability to bring all the components into a balance with the bore size." Wstrnhuntr: "the design of the case DOES have an influence on internal ballistics." Then it gets back to the original question and obviously good arguments can be made for both sides. To confuse the issue a bit more, Gary Sitton once wrote about "The Natural Bullet Weight". To shorten his thoughts does not do it justice. "BUT", basically he believed that for each Cartridge, with a specific purpose in mind, there is a Natural Bullet Weight. Depending on what you intend to do with the Cartridge, all the performance characteristics come together to indicate a specific Bullet as best. Things such as accuracy, velocity, retained energy at the point of impact, wind drift, time of flight, trajectory, and recoil. And there is nothing wrong with including any additional parameters you need for your specific task like: barrel life, report level, powder efficiency. Here you simply list the items as to which is the most important for the task in descending order. Then look to see what Bullet fits those parameters the best. This to me as Mr. Sitton calls the Natural Bullet Weight, is balancing the performance characteristics of each cartridge. It is readily apparent that some Cartridges are easier to "Balance" than others. | |||
|
| one of us |
Wstrnhuntr: Quote: "But by the same token, the design of the case DOES have an influence on internal ballistics. To believe otherwise denies the fact that a handfull of cases have a greater tendancy to accuracy than others. Considering that the gasses must make their way past the shoulder of the case, I dont see how doing so efficently could not be a factor" I totally agree. I didn't touch on this point for a reason. Believe me, the case design and shoulder angle was discussed on a daily basis. I've personally had cases that I went from 25d shoulders up to 40d shoulders 5d at a time on. The only conclusion that I and my friends came to was that usually a sharper shoulder needed a slower burning powder. In the smaller cases even that wasn't always readily apparent. But that fact did lead us to believe that the basic design did have influence. But this post was about accuracy and case design. Now, I am talking about modern case design without a lot of taper and a reasonable shoulder angle, say 25 or 30d or greater. We never drew any conclusions that changing the shoulder angles within those parameters changed accuracy. Powder burning rate, yes; accuracy,well, we just never decided conclusively. That's the reason I stayed away from that on my post. Others may have reached a conclusion. But, I can tell you that we moved a lot of brass around on good case designs and shot them in good rifles over wind flags and also in match conditions. And, we never decided for sure. I would NEVER dispute the fact, though, that the case design does change the internal ballistics. Your analogy of the exhaust system on a car, in my mind, is a good one. knobmtn | |||
|
| one of us |
Hot Core: Quote: "But, it is possible to be mislead into improper conclusions and never be aware of it" For sure. That's one of the problems of experiementing with rifles. They always raise as many questions as they answer. I always felt that if I had benchrest quality rifles and learned how to shoot them I would be able to figure out a lot of this stuff. However, just as I thought I knew the answer another variable would pop up. For example, just changing the lot number on a powder or primer can change the load settings on these rifles. Now, there is another variable introduced. By eliminating the variables as much as possible in the rifle other variables are introduced, or at lest they become apparent. That's why I'm always hesitant to say "this is the way it is" on any of these topics. I think its better to say this is what I did; you draw your own conclusions. By the way,,,this is off topic. Do you remember our postings over the 7mm-08? I'm building one in a 7-08 Ackley. While I've been waiting for the barrel and stock to come I've been shooting the gun a bit. It's a Model 7 youth gun. I'd be curious about bullet weights and what you have to sy about them in that bore size. You can send me a PM or even make a new post if you want. A little further down the road I will probably do that if I don't hear from you. knobmtn | |||
|
| one of us |
Quote: Hey Knobmtn, Yes I do remember. Probably best for you to crank up a thread. That way the Rookies can learn from it. And, you never know who may join in with even better/more experience. I've no experience with the Ackley version, only the regular 7mm-08. | |||
|
| Powered by Social Strata |
 | Please Wait. Your request is being processed... |
|
Visit our on-line store for AR Memorabilia