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can you really "read" pressure signs from a primer if the pressure is not GROSSLY excessive? I recently read that this technique is flawed for numerous reasons (e.g. primers are harder now than days gone by, etc.)and that there is no real way for the normal handloader without special equipment to tell pressures unless they are truly excessive. Any thoughts? | ||
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As you state, they are over-pressure signs! The first method to get close to judging safe pressures is to use a cronograph to compare your rifles or pistols velocity to that of a load manual, and correcting velocity for barrel length. If you're getting another 100 fps or more, and you're primers don't fall out or look funny, it doesn't mean that your operating within the manufacturers pressure specs for that cartridge. The more accurate method of pressure measuring is a piezeo electric strain gauge, ala the Oehler 43 PBL. | |||
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Reading primers is possible, to some extent, but there are a number of variables, and it takes a lot of knowledge and experience to do it. It is not a "flawed" technique exactly, but not many have the ability to do it properly. Even then, the best you can get is "that is mild", "that is warm but OK", or "that is too hot". A better technique for the average reloader is to note resistance to primer insertion. With a high intensity rifle cartridge, if you can get three or four reloadings with NO decrease in resistance to priming, the load is probably OK in that rifle. If the primers start to go in a little easier after five or six reloadings, the load is probably safe but at maximum. If you get more that that with no change in feel during priming, the load is under maximum. This is much easier to judge with a hand priming tool, which I use for all rifle reloading just for this reason. | |||
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Primer pocket life is a good indication - but I also found out that it goes along with case expansion at the web of the case - just above the rim. Fired factory ammo I have measured usually shows no sign of any expansion from unfired rounds. Hot reloads with short primer pocket life (2-3 reloads) have measured .007" expansion. Moderately stiff reloads that allow maybe 6-7 reloads measure about .001-.0025". Somewhere in one of these posts it was mentioned that Vernon Speer used the criteria of no allowable case expansion permitted for maximum reload data - which would allow longer case life with the neck or case above the web eventually cracking. I can look at the primers (my rifles only) and just about tell how the cases will measure out. | |||
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Well I use the same method that rifleman1 uses . I simply have a factory fired cartridge on my bench that I use to compare my own fodder with , havent blown one up yet , so I guess it works ![[Big Grin]](images/icons/grin.gif){kind=icon} .Rudie | |||
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There is an interesting discussion of "reading" chamber pressures in the latest issue of "Handloader" magazine. To summarize the article: many of the classic indications such as a sticky bolt lift, are not accurate reflections of chamber pressures. Measuring case expansion of once fired cases is a useful method; however, none of these methods is extremely accurate. The suggestion is to use the expansion method along with measured velocities to stay in the "safe" zone. Ku-dude | |||
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quote:Hey kynadog, Pressure is one of the least understood subjects for Reloaders and one of the most important. Misunderstanding or ignoring obvious Pressure Indicators can get even the most experienced Reloader into trouble quickly. Less than a month ago a fellow who's input I respect and who actually has more time at a reloading bench than I do managed to Bulge a Chamber because of some "Rookie Level mistakes that he made"(his words not mine). So, it is real important for everyone to pay close attention to what the Pressure Indicators are trying to tell us. Before I go into a lot of detail, let me say up front - Use every Pressure Detection method available to you when working up a Load, because there is "NO" perfect Pressure Detection method. 1. Sometimes you can get good information from the spent Primer condition and sometimes you can't. There are a bunch of factors that can skew these results in addition to the relative hardness of the Primer Cup material. Just use it as "one" of your Pressure Indicators. 2. Perhaps it is better to say that each and every pressure detection method has quirks that can render the information provided "questionable". When observing the results of multiple Pressure Indicators, your confidence level in what the combined information is telling you is greatly increased. For example, I rarely disagree with Pail H's posts, but I disagree with his statement: quote:The M43 is no doubt a fine piece of equipment at $800 + $1200 for a Laptop = $2000, but it also has some quirks that make the Pressure Readings it generates from a Strain Gauge "questionable". First off, there is "NO WAY" to Calibrate(???) it with a "Standard". The problem here is that readings from the Strain Gauges are quoted in PSI which is "misleading" since you really don't know what the Factory cartridge PSI actually is when setting-up the M43. And unless you have access to a $100K+ Coordinate Measuring Machine(CMM) with a very-long high-dollar probe, you are also "guessing" at the thickness of the chamber where the Strain Gauge will be attached. Is the Chamber slightly tapered? If so, that also skews the results. So, the M43 is not perfect. Now, this will seem contradictory with the above, but I think the M43 can provide useful "second hand" Pressure information, but it must be used in conjunction with other Pressure Indicators. 3. Well, there are always the old tried and true Case Head Expansion(CHE) and Pressure Ring Expansion(PRE) methods. They are inexpensive, easy to understand, provide first-hand information and you validate your results by comparing them to whatever Expansion is generated by a group of Factory cartridges. Here you are not involved with guessed at PSI Readings so the actual first-hand Expansion Measurements have some value. But even CHE and PRE has quirks. PRE is the easiest to learn, but it is best not to reload that same lot of cases more than 6-9 times(depends on the intensity of the reloads), because they "work-harden" a little bit with each shot. First off, 0.001" Calipers are not accurate enough and will not work for this. You need 0.0001" capable Micrometers to locate the "High Spot" on the Pressure Ring. www.wideners.com has them for $21 - Item RC87321, or a mechanical digital model for $35 - Item RC87322. Using Velocity alone to indicate Pressure is also a mistake. A few years ago, a person who actually should know better started a "Pressure=Velocity" thought concept. This is TOTALLY FALSE. Look in your Hodgdon Manual for a popular cartridge like a 30-06 and you will soon realize the absurdity of that statement. Many folks also think it is OK since they are using the "Specific Powder", but that is also incorrect. Depending upon the actual design of the Bullet being used, it is possible to get widely different Velocities using the exact same Load. "BUT", if used with other Pressure Indicators, it can provide a "piece" of Pressure Information. After all this, you may be more confused than before. It is a tricky subject. Just use ALL the Pressure Indicators that you know about and if "one" of them indicates something may be wrong, STOP and find out what is going on. If you are interested in learing how to use CHE and PRE as "one" of your Pressure Detection Methods, let me know. Good luck to you. [ 09-19-2002, 19:25: Message edited by: Hot Core ] | |||
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If you really want to know your pressure just send 15 rounds and a check for $54.97 to Western powders' ballistics lab. http://www.westernpowders.com/ Click on "The Ballistics Lab" This lab has been pictured in Handloader several times. I have sent a few loads to them and it takes about 2 weeks to get the data back. | |||
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Hey Sean, That looks like a good idea, but it can also mislead you. For example, if your barrel is slightly tighter than the barrel they run the Test in, then your firearm will experience "Higher Pressure" than what they report to you. Same can be said for the surface condition of the bore, twist rate, chamber dimensional differences, etc. I agree it is one more Pressure Indicator to consider, but don't let it fake you out. Good luck to you. [ 09-19-2002, 22:13: Message edited by: Hot Core ] | |||
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Hot Core I agree, my wife has a 308 for example that didn't read the reloading books, and insists that minimum loads are indeed maximum loads. One firing of a max load will expand the case to the point that the primer will fall out if you try to reload it. | |||
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