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05-24-2016, 12:41 PM
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Pressure testing loads
Granted, a chronograph can give you velocity readings but where can one obtain pressure measurements for their loads?
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05-24-2016, 12:46 PM
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Without very expensive pressure testing equipment you can't do it yourself. You need to rely on reputable reloading manuals.
You can guesstimate over pressure using old techniques such as extraction difficulties, head expansion, primer flattening.
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05-24-2016, 12:55 PM
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In my mind, strain gauges are not all that expensive. The conservative method of doing it is using signs of excessive pressure, but in handguns, those pressure signs are very misleading. Rifles are somewhat simpler: extractor swipes on case heads, blackened primers around the edge of the pocket, hard bolt lift, etc., all mean too much pressure.
Handguns are a different matter entirely. One should rely on the load manuals, in my estimation. Often they are conservative, but I also believe that seldom is another 100 fps worth the risk of personal injury or damage to a fine handgun.
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05-24-2016, 03:36 PM
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You can buy your own private ballistics lab pressure measure....for about $800
https://www.shootingsoftware.com/mm5...tegory_Code=PT
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Last edited by OKFC05; 05-24-2016 at 03:39 PM.
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05-24-2016, 04:00 PM
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Quote:
Originally Posted by fixitfred
Without very expensive pressure testing equipment you can't do it yourself. You need to rely on reputable reloading manuals.
You can guesstimate over pressure using old techniques such as extraction difficulties, head expansion, primer flattening.
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Primer flattening means nothing. Extraction difficulties can indicate soft brass or a rough chamber. Again, it means nothing by itself. Head expansion can also mean soft brass.
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05-24-2016, 04:04 PM
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A good reloading manual is your best guide. Match the load in the book, and you are probably ball park with book pressure. Probably - That's why you always start 10% below the starting load, and work up.
Problem with most handguns, is pressure signs common to rifles tend to be less reliable. By the time shells are sticking, primers are leaking, and case heads are bulging, you are already way over.
Oehler used to make a unit that you attached a transducer to your gun, and measured pressure, as well as velocity, but I don't believe they make it any more. I remember reading it was sometimes difficult to get repeatable readings with it.
There are various ballistic programs that figure pressure based on the info you enter, but I would be hard pressed to believe they are as accurate as tested loads published by the powder / bullet manufacturers. The old Powley Computer is one of the better known.
Larry
Last edited by Fishinfool; 05-24-2016 at 04:06 PM.
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05-24-2016, 04:32 PM
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You simply do not really know.
On the high side of things, the reliable pressure signs one can look for in a rifle don't occur until you get up to the 50,000-60,000 PSI range, well beyond the max of any pistol cartridge you're likely to encounter. Guys run over book all the time and justify it by saying that they haven't encountered a cratered primer, stuck case, etc. When they tell me this, I make a mental note not to be there when they shoot.
The flip side of the coin is that you can also carefully craft a round which won't, say, cycle an automatic properly, but is also running max- or over-pressure. Been there, done that, and wisely backed off before I got within .1-.2 grains of max.
The low side of things is easier to judge--gradually increasing smoke, residue, unburned powder, more erratic velocities, leading, etc. The problem is that everything can go great until you find that 3rd or forth deviation light charge that squibs. There are all kinds of great data for light-recoil loads, and lots of popular low-recoil powders, don't reinvent the wheel.
Don't obsess over pressure. Follow The Book, and apply common sense--it probably isn't a super-great idea to use Low Pressure Target Powder 836-A1 in your .44 Magnum Keith loads, even if The Book says it won't blow up. Don't try and make a cartridge be something it isn't. Your .38 Special can either be one solid .38 Special, or it can be a rapidly-disassembled .357 Magnum. It cannot be both. And achieving consistent pressure isn't the One Final Path To Perfect Accuracy.
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05-24-2016, 04:41 PM
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Quote:
Originally Posted by OKFC05
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Beat me to it!
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05-24-2016, 05:15 PM
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Quote:
Originally Posted by OKFC05
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Neat, didn't know that was out there. Looks like it works similar to the old Oehler system. Any reviews R/E accuracy and repeatability?
Larry
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05-24-2016, 05:25 PM
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I was tempted at one time to buy one of those strain gauge pressure measurement systems, but figured I wouldn't use it enough to justify the expense. Plus, it would be difficult, if not impossible, to use on a handgun, other than maybe on a T/C Contender. Some of the interior ballistics computer programs will calculate and plot the pressure vs. time curves, but I have doubts about their reliability. Be aware that there are several different methods to measure chamber pressure in the laboratory, and they all produce differing results. I have used most of them myself.
At one time there was what was represented to be an inertia-based pressure measurement system for rifles, called the Powley P-Max, but I don't think it was too successful. It looked like a tube that was somehow clamped onto the barrel.
Last edited by DWalt; 05-24-2016 at 05:39 PM.
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05-24-2016, 05:55 PM
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I don't believe that will work on a revolver.
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