The Accurate Reloading Forums THE ACCURATE RELOADING.COM FORUMS Guns, Politics, Gunsmithing & Reloading Single Shot Pistols Case volume vs Barrel length ? Is there a ratio ?Go | New | Find | Notify | Tools | Reply | |
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Welcome aboard. P.O. Ackley did a lot of work on what he described as bore capacity, but like my approach it was based more on experience than on mathmatics. Homer Powley used to put out a slide rule type computer for calculating pressures, velocities, etc. with certain barrel lengths. By and large it is relavant, but in TC factory barrels, some of their rifling designs tend to skew the results from the Powley calculator. You might ask around and see if anyone has a source for these. I am not certain that Homer Powley is still alive even. I can offer nothing in regard to calculations, but have a pretty good feel for what is to be expected. Run something by me and I will give it my best "guesstimation." Don Shearer has a pretty good stock of theoretical sources to draw from. Don, if you are on board, what can you offer our friend across the pond? Mike | |||
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Jurgen & Mike, I have seen essentially nothing about useful barrel length limits for any given chambering. As Mike notes, most everything has been "seat of the pants" estimates based on experience. I don't recall seeing anything in P.O's books on it either. Probably the best bet would be to get hold of a Powley calculator. Mike, Homer died a couple of years ago. When he died, he left all his notes and ballistics material to Ken Howell. Ken lives in Stevensville, Montana, but has been in ill health recently, so I don't know if you can even get in touch with him now. There are still some of the Powley slide rule calculators floating around and occasionally you will see one. Probably the best bet would be to make a post on this forum in several places to see if someone has one. Sorry I don't have more, Don Shearer | |||
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| <MePlat> |
Thank you [ 07-14-2002, 16:48: Message edited by: MePlat ] | ||
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I think that this sounds like "expansion ratio" to me, i.e. the volume of the bore in front of the bullet over the volume of the case. I do think the "best" expansion ratio would be affected by powder burning rate, sectional density, etc., but it seems like 9 to 1 sticks in my mind as being a good "ballpark" number to estimate ideal barrel length for a given cartridge. Bill | |||
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quote:Don, I wasn't quite on track with my response to Jurgen's question about useable barrel length. You are correct in that so far as I can recall, P.O. did not get into the short barrel scenarios, and did not even publish barrel lengths used to obtain the data in his books. I guess what I was thinking is that as the bore size goes up, velocity losses with shorter barrels goes down. Thus the bore size enters into the picture also. Really sorry to hear about Homer Powley and Ken Howell. I never had any dealings with Powley, but when Ken was with Wolfe Publishing, we communicated often. None of us last forever, and the best we can hope for is to have made a difference for the younger generations that follow us. Thanks for the input.... hope all is well there. Mike | |||
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Jurgen, Here in the states New Yorkers have a reputation for answering a question with a question. We call it a "New York Answer." Here are some New York answers for you: What amount of muzzle blast will you accept? What is the minimum velocity you will accept? What level of handling qualities will you accept? What completeness of burning will you accept? I see the question as stated as being quite subjective. It depends on the application and what you want to accomplish. Velocity loss increases as you shorten a barrel with a given cartridge, normally, if you are talking about a high velocity round. In other words, if you take a 26" .30/06 barrel, chronograph it, then whack off an inch at a time and chronograph it at each interval, the velocity loss keeps increasing the shorter you go. Low velocity rounds with fast powders often lose velocity with longer barrels since the powder is burned enough that the pressure has dropped to the point where the gases are no longer accelerating the bullet, and friction between the bullet and barrel is slowing it down. Just for grins, give us some examples of what you have in mind concerning your question. This should be more fun than any theoretical discussion based on mathmatics and hard numbers. Mike | |||
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Velocity loss increases as you shorten a barrel with a given cartridge, normally, if you are talking about a high velocity round. In other words, if you take a 26" .30/06 barrel, chronograph it, then whack off an inch at a time and chronograph it at each interval, the velocity loss keeps increasing the shorter you go. I quit reading gun rags along time ago, but i remember an article on this where a guy did just that, took an old 06 with I believe a 29" bbl and started whacking it off an inch at a time (down to 24-22") to see what was what. The ol' boys have always said velocity would decrease by about 30 fps per inch(I believe) as a rule of thumb and his test pretty much showed it true. But I would think with all the diffrent powders available that a standard would be nigh impossible. | |||
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If you'll look over in the reloading pages of this bunch of forums, you can find where some of the fellas did an experiment with a brand new 223. They cut off an inch at a time and recorded the results. See if this URL works http://www.accuratereloading.com/223sb.html Rick | |||
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| <pshooter> |
With current faster burning powders, Is safe pressure levels the main obstacle between muzzle vel. and bbl. length? Shorter bbl...faster burning powder...faster bullet...higher pressures? Granted this question is like lasic surgery with a swiss army knife, but does it have any merrit? mvm | ||
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| <MePlat> |
Thank You Again [ 07-14-2002, 16:48: Message edited by: MePlat ] | ||
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Greyfox, Interesting study. Hope the ATF guys don't "catch them." On the other hand, maybe the study wasn't done in the States?..... Gary T. | |||
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| <pshooter> |
Do higher pressures alter the burn rate? I think this idea is smothering me! mvm | ||
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pshooter, I can't speak to the higher pressures altering the burn rate, but a certain length of barrel is needed for any given charge to reach maximum pressure, and some powders don't perform worth a hoot at lower pressures. So if the barrel were shorter than was necessary to reach a full normal pressure level, accuracy could be pretty poor with such a powder. One that comes to mind is AA2520. For example, working at the pressure levels we find acceptable for the Contender in .444 Marlin based cases, Don Shearer could not get decent accuracy from AA2520 after a number of attempts with it. On the other hand, those loading with this same powder to higher pressure levels than we condone find that it shoots exceptionally well. It apparently needs a slightly higher pressure level in order to perform well. If a barrel were too short to reach the needed pressure level with a given powder, one could find the accuracy very disappointing. Mike | |||
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| <pshooter> |
Thanks Mike. Is it oversimplifying to say just keep using faster powders untill acceptable muzzle velocities are reached as long as pressure seems OK. I guess it can't be that simple, or there would be no factory velocity wars. mvm [ 07-14-2002, 16:04: Message edited by: pshooter ] | ||
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Mike and others, A slight correction about my testing with AA2520 in the Bellm Boomers. Mike noted that I couldn't get acceptable results with 2520 and that is correct. However, the problem was that it produced such a humongus muzzle flash that it completely defeated the Oehler 35P chronograph. Recall that I do all my testing at an indoor facility where the lighting for the chronograph is incadescent lights through a slit in a baffle with orange filters. The muzzle flash just overwhelmed the chronograph and I could not get ANY reliable velocity data out of about 50 shots, so I don't know what the velocity was. Therefore I abondoned further testing with 2520. I even tried putting up deflector plates with a small hole for the bullet to go through trying to deflect the flash, but to no avail - the flash was just too big and bright. I even bought another can of 2520 thinking my original one might be defective - no. Other powders worked fine. The message that came through to me was that 2520 MAY work OK, but that humongus muzzle flash sure was not caused by normal powder burning - - it was caused by powder that was NOT burned in the barrel. The probability was that the powder was burning for quite a while after it left the barrel - even as the blast crossed over the chronograph which was 10 ft from the muzzle. Little clarrification there. Don Shearer | |||
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| <J�rgen> |
I`m astounded to say the least ! I will print all your answers and add them to my "collection" , what I was wondering , especially in short barrels , if there is a certain case capacity that is way too big with any powder type ?! If my memory serves me right I`ve seen .416 Rigby chambered in a pistol length barrel , this actually made me think about this whole thing in the first place !Is there a way to burn all this powder ?? There must be a certain ratio , thanks so far , J�rgen ![[Wink]](images/icons/wink.gif){kind=icon} ![[Smile]](images/icons/smile.gif){kind=icon} | ||
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Jurgen, I am certain that one could quantify the results of many samples and arrive at a ratio the experimenter deemed acceptable for his particular criteria. But before such a ratio would be meaningful, you would need to address some of the questions I posed above pertaining to what you hoped to accomplish and what you would find acceptable. Such a point surely exists, of course. But there is no single answer. Mike | |||
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quote:Don, It appears that when the pressure is pushed just a little higher than what we are working with in the Triad cartridges AA2520's fireball goes away and it turns out to be a top performer. But this is only where pressures are closer to about the 50,000 psi mark. I have experienced the same fireball with WW760 for example in handgun lengths when I attempted to use standard primers with it. Switching to magnum primers stopped it, and the groups came right in, which should parallel your findings. Mike | |||
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quote:Thatis basically correct, yes. You want to burn as much powder in the length of barrel you are working with as you can. There can be exceptions where a given slow powder will give the highest velocity and good accuracy though, compared to much faster powders. Mike | |||
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| <J�rgen> |
Mike: I know that my question has too many aspects in itself, it turns out to be even more complicated than I thought at first ?! One of your answers above (for Don ) included a little bit of an answer already , it is the pressure factor! But to get back to one of the most extreme examples , the 416 Rigby , is there really a chance (with even the fastest useful powders) to burn almost or over 100 gr of powder in a short barrel (12"-15")without burning 1/3 of it outside ?? My latest addition is a 16" 35 Whelen Imp. and when I planned this whole thing , I figured that the volume of this case is close to maximum !But like you said , there`s no single answer , I thought that there`s a formula (bore dia. , pressure ,volume etc.) to calculate it .Once again thank you very much for all your answers so far , J�rgen | ||
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| <pshooter> |
Jurgen, Thanks for the question. It adresses something I've been wondering about. Is anybody breaking the rules and using "faster than typical" powders in their "rifle pistols"? I may be wrong (usually am) but there are much faster powders than we usually use in our type of pistols so can we try them and still keep our fingers? I do understand that adequate pressure contributes to burn efficiency and consistency and too little powder causes misfires so is too much pressure the main stumbling block? Maybe cannon powder will work (hehe). Still trying to find a 3000fps, 150gr, 15"bbl combination. mvm | ||
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Jurgen, no, I doubt that much of the 100 gr. of powder in a 416 gets burned in a short barrel. For that matter, toss a match into the sweepings on the floor in front of an indoor firing range sometime. Even the fast powders used in normal handguns like the .38 Spls., 9mms, and .45 Autos don't burn completely. Don shoots in an indoor tunnel. Any comments about the unburned powder in front of the firing line? Don, I have not played with the Powley computer, but as I recall, one can derive some information from it useful for Jurgen's question, even though it does not factor in the subjectivity of what is or is not acceptable to the user. Mike | |||
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| <J�rgen> |
Hi Mike , this is what I meant , lots of wasted , unburned powder !But what if we use even faster , bulkier powders ? While staying within the pressure limits , is there anything that keeps us from experimenting ? | ||
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| <J�rgen> |
I forgot an example : I usually load N140 in my 308 Win. (22" barrel) but I`ve tried N135 in my 16" Encore , although I`ve not measured it yet !I`ll even go to N133 soon , N135 looked very promising but still unburned powder granules.....!I`ll keep you posted ! | ||
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