In my view, it is more accurate to say that the same amount of area below the pressure trace for the bullet's passage through the barrel will result in the same muzzle velocity. The peak pressures can be different and you can get the same velocity; conversely, peak pressures can be the same and you can get different velocities.Boomer said:It takes pressure to push a given bullet to a given velocity from a given barrel, and it takes the same amount of pressure each and every time. These results are repeatable within a given combination of components and firearm.
Actually, I am of the opinion that about all that can be said for case head expansion measurement is that it is about one step above simply guessing at what pressures are. Ken Waters always said it was not particularly reliable, just simply better than nothing at all - Waters never claimed this was an excellent way to evaluate pressures, and some writers and handloaders have forgotten or overlooked this. There have been numerous discussions in magazines and on the internet regarding this over the years; this is one I was able to quickly find:The head expansion measurement is only meaningful if it is conducted with the same make and lot of brass from test to test, and I would assume with brass that has been fired the same number of times, but ideally with new brass.
I'm not sure I can completely accept that, assuming I clearly understand what you're getting at.By comparing the chronograph's findings with either previously chronographed results, or by comparing the findings to published load data, the chronograph will tell you every time if your pressure is within acceptable limits.
Again, a chronograph will NOT tell you what the maximum pressure of a load was - you can have pressure spikes that still result in "normal" muzzle velocities.If there is a rise or drop in pressure due to; temperature, change of components, or for any other reason, the chronograph will show that change in pressure by indicating a change in velocity. It is up to the tester to determine the cause for the change in pressure - and no software, hardware or loading manuals will be able to make that determination for him.
We're definitely going to disagree on that one. The number of trials you do in ANY statistical analysis (which is what you're doing here, whether you're testing velocity, pressure, or the number of times you'll roll a dice and get a six) has everything to do with the accuracy and predictability of your results. A small number of trials leaves any statements regarding accuracy and predictability as essentially meaningless.As with any testing, the larger the test group the more accurate the results, but that does not mean the results of a small test group should be disregarded, or that data from a larger test group will be produce data that would influence the findings of the smaller test. The testing is for an individual shooter, with an individual firearm, and is done at a specific location.
From a statistical analysis point of view, that is irrelevant. You have a population of trials you are using for your analysis; the size of the population and the results of those trials are what matters.The purpose is not to test commercial ammunition which might be used in a wide range of firearms, by thousands of people, in the far reaches of the world.
Doppler radar trials of newer chronographs has produced results showing accuracies around the 99.8% mark. That gives you a +/- error somewhere around 2 fps at 2000 fps. That's for newer, smaller chronographs with 2' spacing or smaller - I don't recall any tests where the screens were then mounted much further apart to enhance accuracy and remove that 2 fps potential error. It also occurs to me that at some point as you increase screen distance you induce error - as a gross example, if I put the screens a hundred yards apart, do I now have an accurate measurement of velocity?The farther apart the chronograph screens, the more accurate the results. I find 6' is convenient for my purposes, and I am confident that small shot to shot variations are true readings.
Good thing I made allowances that he might be a geologist, forester, timber cruiser, or whatever, then...Gatehouse said:Ha Ha...Funny...
Camp Cook is actually a play on his name. Last name is Cook.![]()
Reduced loads are an entire subject unto themselves. And many reduced loads are in the 600 - 800 fps range, which is another dimension entirely. However, I think I've illustrated the point that a chronograph can not tell you what pressures are simply by providing the muzzle velocity. You can try and avoid being fooled by your chronograph by using certain powders and primers - but the chronograph won't tell you whether you're getting pressure spikes or not.Boomer said:Rick -
Your point concerning pressure spikes is taken, but the results obtained with reduced loads can be optimized by using easy to ignite powders and a strong primer. I have found when shooting light (1200 fps) loads in my .375, a combination of Unique with a magnum primer, gives excellent accuracy regardless of where the powder lies in the case.
Okay... I can somewhat accept this. But where, for example, do I find "several" reloading manuals that give me the load data for a .308 Barnes TSX loaded with IMR4350 and a Federal Large Rifle Primer?However, if you study the data from several loading manuals and determine that the maximum velocity of a 180 gr bullet from the .30-06 is 2700 fps when loaded with propellant X, when your chronograph reads 2700, it's a good bet you are very close to the maximum load with that combination of components.
The issue isn't whether it is one rifle or a thousand; it's whether the number of trials you are performing has any statistical value whatsoever.I am not going to disagree that a larger test sample is the more accurate than a smaller one. However, I will point out that we are speaking about obtaining results for one firearm, with one particular load, and therefore I maintain huge test sample is of little practical value. If, based on 10 rounds, I determine that my velocity is 2700 fps, but you disagree because your testing of 100,000 rounds indicates that the true velocity is 2710 or that the standard deviation is a point or two different - I won't care.
One trial does not provide any useful information to you about load performance - or flipping quarters.The reason I won't care is because your results won't provide any information that will be useful to me in the field, and because I am not concerned about how the load will work in a thousand different guns, I am only concerned about how it will work in my gun. Consider your example with the American quarter - you cannot make assumptions for all American quarters, but you can certainly make a reasonable assumption based on the history you have developed with that one particular quarter for how it might react to being flipped in the future.
Oehler is gone from the personal use chronograph market now, although they still supply parts and service for the time being. I'm going to take a guess here and say the reason for that is quite simply that their pricy systems could not compete with the Chronys, PACTs, CEDs, etc - especially after people started testing various systems against each other to see if any were particularly more accurate/inaccurate than others.If you have seen test results showing that chronographs with 2 foot spacing are accurate to 99.8%, that's fine, but it isn't what the folks at Oehler say concerning their products, and I can only comment on the machine I have.
Well, I can't resist... stats again... if you were using a recreational GPS like a Garmin, Magellan, etc, your range was 1038 yards +/- about 60 yards. If recreational GPS's could determine the distance between two points to within a yard or two - or even ten yards - we wouldn't be dragging Leica's, Trimble's, and TopCon's around in the bush that require tripods, car batteries, etc, along with a backpack to carry them on.Useing this proceedure last winter, I fired at a target GPS'd at 1038 yards from my firing point, (it was a convenient snowdrift) and my rounds struck 4" low on the paper.
Well now, for somebody whose last post was about "armchair theorists" - when you don't have a clue who you're addressing or what we do for a living, you're a pretty amazing guy yourself.Camp Cook said:"WOW" Rick you really amaze me...
How do I even respond to such ignorant assumptions.
So... if I were to assume you have never actually shot a bear with a handgun yourself - nor seen anyone else have to shoot a bear with a handgun in self defense - I would be wrong?Let me put it this way for you...
All of your assumptions are wrong...
That's right. In my office, out here in the sticks... whether it's my place in Montana or my place in the Kootenays. I don't have to travel more than about 20 minutes from either house to be out hunting black bear, grizzly bear, and cougar - the last elk I shot was ten minutes from the house via mountain bike. Meanwhile, you struggle daily with survival in the urban sprawl that is the Lower Mainland, correct? I understand that dealing with rush hour twice a day in the 'burbs, surrounded by several million people, can be a real killer. I feel your pain, you ol' bush rat you... it must be hell living in that wilderness.Where did you say you are right now?
Something about sitting in an office...
Calum said:
Calum said:
I can agree with you on velocity plateauing, but it is easily possible to be well over SAAMI spec before seeing marks on cases, sticky bolt lift, etc. If one doesn't care whether or not they're a bit (or maybe more than a bit) over SAAMI spec, then perhaps that is not an issue. And there's more than a few handloaders out there that keep right on going until they do see physical signs.Boomer said:If I am paying attention, I will probably notice that the velocity of my incrementally increased charges has plateaued prior to the difficult bolt lift.
Velocity correlates to the area under the pressure trace for the bullet's passage down the barrel - not to the highest pressure achieved. If you believe you can not have a pressure spike without either higher velocities or warning signs in one single instance of that pressure spike... well, that's interesting.Any pressure spike of significance will show up as higher than normal velocity. If the pressure spike does not result in higher velocity, and if it does not leave a warning sign on the case it is insignificant. If the a detonation occurs the velocity will be lower, but the shooter won’t care, because he’ll be combing iron out of his whiskers
Obviously, you've been having difficulty following my argument.If we were to follow your arguments to their full extent, no one but a statistician could hit anything with a rifle at any range, even if we even knew what that range was.. No one but a statistician could load accurate ammunition.
G37 said:Ok... I've got a Non-Restricted rifle with some 10rnd AR mags... seriously:
.223 remington (18.5" barrel) vs 10mm (5" barrel) (any bullet for either is allowed, please specify)
I know a shotgun would be ideal and what I'd carry (if that was a concern for me)... but the kid in me wants to know which one of the two you'd rather have in a defensive situation versus say... Mmmm... I dunno... a bear?
Anyone?