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I read a lot about this here on AR and I'm wondering what the opinions are. Some use the chronograph as a pressure tool and some don't. It's being discussed on another thread and I didn't want to hijack that thread to discuss this single issue. So what say you? Can the chronograph be used to measure pressures or is there a proven correlation between velocity and pressure? | ||
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in my experience it is a helpful tool, but not a stand alone indicator. even if we are using all the same components they will vary some from lot to lot and of course we will be using a different firearm. sometimes chronographs vary from one to another in their readings. barrels can be fast or slow also. atmospheric conditions and altitude will also cause variations in velocities. velocity is like a new car, always losing value. BC is like diamonds, holding value forever. | |||
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I firmly believe, as so do a lot of folks that a chronograph is the single most important tool available to the handloader. In my opinion, things like flattened primers, sticky bolts, case expansion, etc are indicators you've well exceeded acceptable pressures. jorge USN (ret) DRSS Verney-Carron 450NE Cogswell & Harrison 375 Fl NE Sabatti Big Five 375 FL Magnum NE DSC Life Member NRA Life Member | |||
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If you use the exact same brand and style of powder, primer, case, and bullet as the book you can expect similar velocities. Keep in mind there will be variations in speed due to different barrel lenght that needs to be acknowlaged, and temp will have some small influnce. If say for example, speer claims 50 gr of powder "X" with their bullet "B" and primers in a specific case gives 2950 fps with a max load from a 24" bbl. When you chrono your load with the same components, but 1gr less powder you find your velocities are running 2900 fps out of your 22" bbl. You can be fairly sure you are in the same pressure RANGE as the max load in the book. This doesn`t mean you are getting XXXXXX psi, just that you are seeing similar pressures as Speer stopped at when testing their data. Changing any of the components will alter the load and the velocity won`t be as accurate an indicator but still IMO is useful.  ------------------------------------ The trouble with the Internet is that it's replacing masturbation as a leisure activity. ~Patrick Murray "Why shouldn`t truth be stranger then fiction? Fiction after all has to make sense." (Samual Clemens) "Saepe errans, numquam dubitans --Frequently in error, never in doubt". | |||
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This is an excellent question and one I hadn't thought much about before today. I called Ty at Barnes with some load pressure questions. Seems that my old 300win mag load (developed under Barnes 3 manual) is now over max in the new Barnes 4 manual. Ty said they spent alot more money on firing mechanisms in the latest manual. Therefore the chambers tended to be tighter and pressures were increased with smaller powder weights than in the previous manual. His advice was to chrony the load I developed a couple years ago and compare it to the new max load velocity. He said that was the single best way to determine if it were too hot or not. I suspect he knows what he's talking about. Seemed to be a quite knowledgeable young man. | |||
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Interesting. So what should one expect in a situation were manuals differ greatly on powder charge and velocity using the exact same components and barrel length. Example, 300WSM 190gr HPBT, 24in barrel 1-10 twist, Win brass, WLRM primer. In Sierra #5 H414 it lists 62.9gr @2800fps and 65gr Max @2900fps. In Lyman 48 it takes 61gr(Max) of H414 to reach 2844fps. That's two grains less powder with an increase in velocity or 44fps. | |||
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It has always bothered me that the guys with all the lab equipment can disagree so much about loads. Looking at a lot of different manuals and comparing results can be frustrating.....but then it's why we work up our own loads using the cumulative data from several sources. Even Hodgdons data varies substantially from what they now have on the internet and what they published in their hard cover manual #26 When it comes to pressure indicators, the chronograph provides us with a piece of information....nothing more. I consider it valuable information but not to be considered correlated to pressure. One should never expect to reach velocities published in books by ignoring other pressure indicators nor should one stop load development because velocities are high when all other pressure indicators are totally absent. I have a .308 Win shooting 180 grain accubonds at 2,740 from a 20" barrel with absolutely no pressure signs at all.....not even flattened corner radius in the primers.....it makes me think the chrony is off!.....but it's not! It's a heavily compressed load for elk hunting and I'd never had reached that velocity if I quit when I reached factory velocities or other published velocities.....but far worse is the idea that one can keep shoveling in the powder until he reaches a certain velocity....it's simply not good practice.
Here's a statement that I cannot concur with at all.....it simply isn't true and the folks at Barnes should want to retract it! I'd fully concur that if, in the process of working up a load, one reaches factory published velocity, he has a right to think he may be nearing max (SAAMI) pressures even though he sees no other pressure signs....in fact he may have already exceeded that pressure. But one simply don't know.....It's a piece of information.....nothing more....it's not a pressure gauge or a "stop (or worse) or go sign"....it's well known that in most rifles the brass case is the weak link and the brass should tell us when it's too much......not the velocity. Other reloaders can do it anyway they choose....it's their call but I like my chrony....it furnishes reliable information about velocity.....nothing more.....and it does indicate that I may be approaching or have reached significant pressures.....but I want to read the brass as my primary pressure indicators. /////////////////////////////////////////////////////////////////////////// "Socialism is a philosophy of failure, the creed of ignorance, and the gospel of envy, its inherent virtue is the equal sharing of misery." Winston Churchill | |||
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Perhaps it's because I started handloading long before chronographs were readily available to handloaders but I NEVER use a chronograph when working up a load. Several times a year I set it up to see how fast my bullets are going mainly to satisfy my curiosity. For those of you who use them for load workup, it's probably a bit of useful additional information as long as you don't think you can push a load just because your bullets are going 50 fps slower than the manual says they should be. I don't take just one sign of pressure and run with it but take them in concert. 1. I fairly much disagree that one can't tell about pressure by looking at primers. What can be said is that one can't say the primer appearance from high pressure in one gun will be the same as that in another. You have to take the primer appearance in each gun individually and correlate it with other characteristics of the gun you are shooting. A pierced primer or primer leak always indicates very excessive pressure unless there is a quite bad firing pin. 2. One of the most useful pressure signs is how the bullets behave on paper. This works best if you're shooting a gun with good potential accuracy. Groups start out big, tighten and then start widening again. I always stop where groups are the tightest which is generally 3/4 of the way to what the manual lists as the maximum load but occasionally it ends up being a bit over the manual maximum. 3. A sticky bolt is a definite sign of excess pressure. In a break open gun like a Contender or Encore which I shoot the most, slight stickiness when opening the action is the norm with factory ammo so is a good indication of a handload that has been pushed far enough. For weaker actions like pump, semiautos and lever actions it's best to slavishly stick with manual recommendations. 4. Case life, loose primer pockets, etc. are indicators of pressure but you don't get that information until you've reloaded them several times. As for the Barnes manual; there is a lot of useful information in it but, in my opinion, the older manual had a lot of pretty hot loads; hotter than I ended up shooting. | |||
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I don't think so! You can *hope* to get equivalent velocities, but very often (mostly?) you are below what the books "promise"! At least that has been my experience. - mike ********************* The rifle is a noble weapon... It entices its bearer into primeval forests, into mountains and deserts untenanted by man. - Horace Kephart | |||
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There were a good many folks on the Pressure Indicator thread who believe you can use a Chronograph as a Pressure Indicator. For those of you who do believe it, "What is the Conversion Factor from "fps" to "psi"? | |||
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Hot Core I see you are looking for your usual arguement. Several on this thread and numerous on other threads have explained to you over and over and over again that the chronograph does not tell pressure. Thus there is no "conversion", got it? I doubt you do but I thought I'd be polite and ask anyway. The use of a chronograpgh gives an indication of pressure. Taking a modern high pressure cartridge for instance; if you are 1 gr below what manuals say is max but are equalling or exceeding the published velocity of the 1 gr higher load you are getting up there in pressure. The use of the other pressure indicators along with the chronograph gives reloaders a much better picture of what their reloads are doing. To get fps requires pressure. Given a particular powder the higher the fps the higher the pressure. Simple for the rest of us to understand. Larry Gibson | |||
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Yes, indirectly just like sticky extraction and primer signs.
Not necessarily. The ambient temperature you're doing your shooting at, chamber dimensions, barrel diameter (there can be very minor differences even in same caliber barrels), different powder lot and other factors can all cause differences in velocities not always correlated exactly with pressure between different firearms.
I guess a chronograph gives a better picture of how reloads are doing but in working up a load, I don't find them very useful because I care much more about group size than about what velocity I'm getting. One of the results of too high pressure is deteriorating accuracy at which point I stop anyway regardless of what the pressure is.
You already kind of said that. Also, I've heard there is a point where pressure continues to increase and bullet velocity actually falls. Since I have no way to measure pressure, I've never personally confirmed this. | |||
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You’ve “heardâ€â€¦..well I’ve heard that if a dog has a square ass it can sh*t bricks! Just because I’ve “heard†it does not make it so. With regards to what you heard; fact is that velocity does not “fall†(assuming you mean the velocity gets lower). The velocity, in some instances, with some powders just does not increase as fast after a certain pressure level. Nice thing about that is that if you are using a chronograph you know when that is. The lessening gain in fps as the powder cahrge is increased tells you. That lessoning of velocity gain tells you when the load has reached maximum efficiency with the powder/bullet combination you are loading in that cartridge. The chronograph also tells us when the powder starts to burn efficiently. The rest of us understand this. You don’t because you don’t use a chronograph. That is your loss. Larry Gibson | |||
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Not to measure pressure, but yes, most definitely to estimate pressures. Muzzle energy is directly related to breech pressure. To determine muzzle energy you first need to determine velocity. Increasing muzzle energy can be done only by making a proportional increase in pressure. If the maximum pressure of loads producing energies in a given range are known, the probable pressure of other loads in that energy range can be calculated with a reasonable degree of accuracy - provided the bore size and length are similar, powder has a suitable burning rate, the bullet to bore fit is similar, the bullet hardness and bearing surface are similar, and other myriad variables are similar. In olden days it was quite common to estimate pressures this way. Of course, it was necessary to have access to data from actual pressure measurements but many manufacturers maintained and published this information. Today, computer programs do all the work for you and if you're smart enough, you can use the information from these programs to "reverse engineer" estimates of pressure using the velocities from your chronograph. Not something for the casual handloader to attempt, but doable none-the-less. JMHO Ray Arizona Mountains | |||
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Like vapo said, it's a piece of information. While you can't "measure" pressure w/ a chronograph, there are no free lunches. Higher vel. often mean higher pressures. Using a chrono & loading manual can keep you out of trouble. When you get to publshed vel. you are probably close to safe limits of pressure.Combine that w/ normal pressure signs, bolt lift, primers, etc. it's helpful. LIFE IS NOT A SPECTATOR'S SPORT! | |||
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This is the kind of faulty misleading  that continues to flim-flam otherwise well educated people (and at least one fool.  )For you Beginners, the Pressure might be higher, might be lower, or it could rarely be the same. You simply don't know what the Pressure actually is by looking at Velocity. Too many variables in the Cartridge Components from Lot to Lot(even if they are of the same manufacture) and same-e-same with the Chamber/Bore Dimensions and Surface Finish in the firearms. You will notice no one will provide a Conversion Factor from "fps" to "psi" - because it does not exist.  | |||
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onefunzr2, thanks. That is what I thought. Just wondering if others saw it the same way.
It appears I have opened a can of worms however.  | |||
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Let's just paraphrase the last sentence to read, "What is the Conversion Factor from "CHE" or "PRE" to "psi"? It appears to me that observing fps, pre, or che are all useful indicators. Nothing more. Ken O As it was explained to me many years ago, "I feel sorry for those who think ballistics is an exact science. They just don't understand the problems." | |||
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The chronograph is a great instrument for measuring the velocity of the bullet. It can be an aid in monitoring the pressure of your load as well. If you are getting near the max speed as published by say 4-5 reloading manuals, it is prudent to watch for signs of excess pressure as you increase the load upward from there. The majority of shooters on this site will give you all the signs to look for excess pressure as gained from their many years of experience. When you start to encounter many of those signs you need to evaluate your continued progress in the search for higher speeds. You will also find one poster who believes the world is wrong and only he knows the pressure indicators. My advice is to use the ignore button and ignore the same. | |||
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Just thought that anyone who made it this far down this thread should re-read Vapodogs post. It is spot on, IMHO. | |||
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Hey Dr. Oehler, I do not remember anyone ever claiming you could tell what the "psi" happens to be with either CHE or PRE. If you have a Link to anyone saying that, I'd be interested in seeing it. You can however do an extremely accurate PRE comparison to what ever unknown Pressure Factory Ammo happens to be and know you are at a SAFE level. Huuuuum, come to think of it, you can do that for about $30 with a 0.0001" capable Micrometer. Or that is really all a person outside a Lab can do if he spends $3000 for some of the Haphazard SGSs (including the Laptop) on the market. But there is an additional significant difference. The Haphazard SGSs flim-flam some folks into making a very unsafe assumption. Even though they had to guess at the Chamber Dimensions, used a Fudge Factor(whether they knew it or not) and the entire fiasco is Non-Calibrated, that still does not alert some of them into reality. We see it posted here on occasion, but not nearly as often as it used to be, that if the SAAMI Spec is say 58kpsi for a Cartridge, some of the HSGS users think if the Factory Ammo registers 51,623psi(as if the last 3-digets are significant ) that it is OK to go right on and keep dumping in Powder until they get to the 58kpsi. Pitiful!----- Glad to see you still helping keep all of us straight here at AR. | |||
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Hey Grumulkin, It is possible to see the Pressure drop off with PRE using "some" Case/Primer/Powder/Bullet combinations, but not all of them. The Velocity will drop off on those specific combinations too. Both PRE and Velocity will begin giving erratic readings if shooting is continued at those levels and it is a real danger indicator of a non-predictable Load. Best of luck to you. | |||
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Dr. Oehler Well said. As we see, Hot Core is just looking for his usual arguement. He has no interest in learning or advancing. Larry Gibson | |||
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I think I will have to disagree with that statement somewhat. Ballistics IS a science - Physics to be exact. With undeniable and unbreakable rules and laws set down by Mother Nature. Otherwise we would not be able to write ballistics programs and missle and space programs would be shots in the dark (pun intended). If ballistics is not a science, what is it? Smoke and mirrors? Voodoo? Ray Arizona Mountains | |||
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Ballistics sometimes uses science and engineering to justify old empirically derived recipes. Those who use a chronograph to check their pressure in a strong rifle should be left on that level of reloading. | |||
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Such as . . .? Any examples? And I don't really think that anyone has said that you can use a chronograph to measure pressure. At least not me. What I did say was that it is possible to reasonably estimate pressures if you have an accurate velocity reading and enough comparable and suitable data from other actual pressure measurements. Ray Arizona Mountains | |||
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Of course, ballistics is a science. The examples of exterior ballistics you quote even approach being an exact science. Throw in an unknown atmosphere and an approximate drag function and we may have a good approximation, but not exact. Throw in the interior ballistics of typical small arms, and the "exact" becomes a little more fuzzy. Those sacred equations describing the actions become approximations, and there are many parameters we can't recognize or reliably measure them even if we do recognize them. If things were exact, there would be no lot-to-lot variation of bullets, powder, primers, or brass. There would be no variation from one "identical" gun to the next. My personal opinion is that many (myself included) tend to gloss over the many minor variables that influence both interior and exterior ballistics. The variables and their influences may be exact and scientific, but we don't measure them or include them in our calculations. This reduces our "exact science" to a "good approximation." The problems appear when users believe that the results of our calculations are exact. A fellow engineer once explained it as, "If it works on paper, it will work in the real world. If it works on paper, but doesn't work in the real world, then you didn't consider the entire problem in your calculations." If we consider ballistics an exact science, we fall into the same trap. Ken O As it was explained to me many years ago, "I feel sorry for those who think ballistics is an exact science. They just don't understand the problems." | |||
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lets look at two opposite situations..... 1.) A reloader has no pressure signs from the rifle or brass and his chronograph reading shows 2,700 FPS.....the book shows 2,700 as max velocity for their tests......the reloader decides to stop and call it quits as accuracy is good and he's satisfied with his performance. This is a happy camper!!!! He could have progressed to 2800 and maybe even 2900 but made a decision based on his own reasoning!!!!! 2.) A different reloader with a different gun is looking at the same data.....his chronograph is reading 2,550 fps and he is having very flat primers and some sticking of the bolt handle upon ejection. He sees the manual shows 2,700 as max and decides to add another 1/2 grain until he reaches the max velocity!!!!! Both scenarios are quite possible and even common. In both cases the reloader used his chronograph as some sort of pressure tool.....an indicator of sorts..... and obviously one reloader making a very bad decision.....at least on the merits stated!!! Reloader #1 can actually be helped by this type of thread as he just might wish to push the limits a bit more some day.....but until then he's a conservative reloader and will likely have a long and happy reloading career. Reloader #2 won't learn a thing from this thread.....he has no clue and can't find a clue store to buy one!!!! He'd be much better off if his chronograph was broken.....he's using it the wrong way!!!! I think we've all seen both of these reloaders and can relate somehow..... The velocity again is information....it's how we use that information that is critical!!! Suggesting that pressure is strictly related to velocity is very poor reasoning....it simply isn't the case at all! /////////////////////////////////////////////////////////////////////////// "Socialism is a philosophy of failure, the creed of ignorance, and the gospel of envy, its inherent virtue is the equal sharing of misery." Winston Churchill | |||
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I am on the same page as you, vapodog. If a reloader has two 6mmBR rifles, one with a bushed firing pin, and one with the stock firing pin. How will he know the max load for each in a work up? A chronograph? Of course not. Cheechako, Go write a load book with individual pressure limits for my above examples. Your "science" will be quantifying the empirically derived recipes. | |||
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Yes, that is for whatever the reason, what concerns me the most. And there are folks in this thread who will never believe it, even though "Dr. Oehler" said it. ----- By the way, some time ago you mentioned in a thread words to the effect that you now encourage folks to start at the Minimum Manual Load Levels and to STOP adding Powder when they get to an Accurate Load. The words might not be the exact same, but I believe it is similar to what you said. If that is incorrect, please correct me. The more I've thought about it, the more I agree with that line of thought. I still like to use the Creighton Audette Method of Load Development, and your comment ties in with it very well. | |||
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mausernut You lost me. None of your post made any sense. Ray Arizona Mountains | |||
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It would be more useful to look at the gain in energy (E=½mv²). The energy gain has an almost linear relationship to powder charge increase, but only to a point because as the pressure increases so does the energy conversion efficiency. BUT, ... something else happens. Bullets deform under pressure! So, it is possible that at some point, the bullet deformation will increase the drag of the bullet in the bore resulting in a smaller gain in velocity. At worst, an actual reduction in velocity can occur. The pressure, of course, then goes through the roof. The phenomonen is also sometimes responsible for worsening groups at higher pressure. All this has been covered before. Regards 303Guy | |||
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The above was stated in support of a contention that velocity changes always indicate whether pressure is rising or falling. With that in mind, please consider what follows below. "This is true in some instances, but it is NOT true in others. Using exactly the same powder, cases, bullets, primers, and rifle, I have personally experienced situations in which continued increases of powder charge produced LOWER velocities. One such instance was with a .300 Wby Mag, using TCI 5050 powder, Federal 215 primers, Nosler 200 gr. Partition bullets, and Wby brass. After 93 grains of powder, velocity levelled off, then at 95 grains, began to fall. So, are you going to tell me pressures fell as the charge went up? Sorry, but I don't believe that according to case/primer appearances & measurements. So how is that velocity loss possible? Well, it is possible because expanding gas in a cartridge case is not a smooth uni-directional flow of gas. It is a roiling, boiling mass which not only hits every limiting part of the container (cartridge case interior), but which bounces back and forth many times off those surfaces and produces both harmonic and destructive (disharmonic) wave peaks and valleys. Wherever two or more pressure waves coincide (harmonize) within the pressure vessel, the pressures are higher...where they do not coincide but collide, they may partially cancel each other out and be lower in that part of the case. The point here is, enough pressure can be created in a specific very small area (where the waves harmonize) to potentially even breech the walls of the pressure vessel (the cartridge case), without increasing the forward pressure of the gas flow which moves the bullet. So peak pressures at certain points in the cartridge case can be significantly higher, without velocity increasing, or even being as fast as at a slightly lower propellant charge weight. To that extent, the old "rule" about expanding gases applying equal pressures in all directions should not be taken as an absolutely true description of what is happening over time. I suspect it is also why race car engine design engineers can design combustion chambers to get more power out of less fuel. A chronograph can indicate when that situation is reached or about to be reached, but it cannot tell anyone what is happening to absolute pressures in ANY specific part of the cartridge case. Without specific pressure measuring equipment monitoring various parts of the cartridge case, we just can't know what pressures are in either relative or exact terms. What we can do, though, is observe the dimensions, working life, and other such characteristics of our fired brass. That way we can see if the pressures, whatever they may be, appear to be potentially putting us in harm's way. If brass condition appears sound, accuracy is acceptable for the job to be done, and velocity likewise, we likely have a pretty good load. If brass condition is unsound, regardless what else applies, the load is likely less than a desirable one." | |||
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Hot Core said; vapodog said;
If you read between the lines I think you will pick up that Hot Core has seen this too many times! vapodog, is saying it directly! The correlation between pressure and case deformation is a direct one whereas velocity has a correlation with mean pressure. It is possible to have a higher mean pressure and a lower peak pressure in one cartridge/rifle/load and a lower mean pressure and higher peak pressure in another (even just a different load in the same rifle). It seems we have a group of intelligent and knowledgeable people on this thread, each with a different perspective, contributing to a good and interesting discussion.  It has cirtainly set me thinking! I am going to re-visit my loading practices as a result of it. (Just to make sure I haven't missed something. I'm sure I must have - I have never done anything withou making some mistakes.  )Regards 303Guy | |||
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