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I have....and still I say...  /////////////////////////////////////////////////////////////////////////// "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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Your extrapolation of velocity and pressure is WRONG. I used to believe this concept, not anymore! I bought a pressure trace a few years ago, great tool, and it clearly shows that some barrels are fast and some are slow even though pressures do not alter much. I have a 4 groove 1:10" twist 26" barrel that with the SAME pressure as a 6 groove 1:10" twist 26" barrel on the SAME action gets well over 100fps more velocity with NEAR IDENTICAL pressure, yes the loads between the 2 are different, but the pressure is within a few hundred psi of each other. How does that correlate to your theory? I have seen this on several occasions, I have also seen the same LOADS run anywhere from 20fps to over 300fps difference, higher or lower, in several rifle barrels, not all were pressure tested, but those that were showed that some barrels are faster than others regardless of pressure. I think you fail to realise that there are bigger variables in rifle barrels that aren't taken into consideration in QL PREDICTIONS, such as bore size, groove shape, width, depth and number of grooves and even the twist rate changes pressure. Cheers. | |||
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How do you calibrate your pressure trace? AIU | |||
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There is no way in hell anyone can "interpolate" accurately between velocity and pressure! I have been reloading for close to 50 years, and have had literally hundreds of different rifles through here. Each one is a law unto itself - sometimes to the extent that defies everything one has learnt previously. I have had 5 Mannlicher rifles, all the same model, all in 270 Winchester, all brand new. I checked all 5 with Norma 150 grain factory ammo. The velocity difference between them was over 150 fps!!! I have had BRNO rifles in 243 Winchester, that blew the primers on loads lower than the starting loads in a loading book. I have had rifles from many different manufacturers, in the same model and caliber, that varied in so much in what loads they will digest safely. | |||
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How can this be that it is marginally true and not substantially true? What is the use of reloading manuals then that is supposedly based on either CIP or SAAMI standards in certified tests barrels where pressure testing is done based on certain generally accepted principles? Obviously each individual gun (pressure vessel) will differ from the "test" barrel used and that is why each gun system has its own VC curve even if it is the same powder that is listed in the reload manual. It has to do with internal dimentions of the throat and barrel since minimum and maximum tolerances are laid down by industry standards (CIP and SAAMI). Reload minimum and maximum loads per the manual is the best guide we have have for the novice reloader where on starts low and work safely up with in the band of minimum and maximum. Point is the correlation of velocity achieved to pressure is a positive one and not a haphazard one or one that is "marginally true". Recommended reloads in the manual specify mostly a specify bullet weight and type of powder to narrow things down between a minimum and a maximum amount of powder of a specific type that is to be used. These recommended loads have been used based on tests and not thumb-sucks, I would submit.  Santa Claus | |||
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/////////////////////////////////////////////////////////////////////////// "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 agree with Saeed. I have extensive experience with many barrels chambered by the same reamer, by trge same smith using the same loads/components. (223 Wylde, Green Mtn SS button rifled BBl, my reamer used only on my barrels, headspavced tp the same bolt in an AR15 service rifle. The chronograph has read a spread of over 150 fs using the same lot of ammunition ( all carefully assembled by me, using the same Lake City 07 cases, same lot of Rem 7.5s, and the same jug of Varget, the lot of 80grain Hornday Amax bullets etc). Some show no conventional pressure signs, other bbls have popped primers/expanded case heads, most show higher velocity when new, a few have increased velocity after a few hundred rounds. One would not shoot well at all, and showed the greatest signs of high pressure ( extractor/ejector marks, loose primer pockets). Perhaps the best advice is to load carefully, stay at or below max loads, examine cases carefully if using multi-reloaded brass, trim, anneal etc. Pay attention to throat length/seating depth/ bullet jump/contact. Some brass is known to be very soft in the head ( in 223, that would be older small letter federal brass). Be careful, wear eye protection. | |||
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This is the reason why reload manuals can attach suggested velocities to minimum and maximum loads because there exists a relationship. This relationship will differ somewhat for each rig due to other variables such as throat and barrels tolerances when the same bullet and load is being used. And this is the reason why we compare our VC's with the manual to understand how our pressure curve would compare with the manual's even though we never try to pin the exact pressure down. Some people never compare VC's because they lack the understanding of comparing VC's, and yet it is such a simple guide .... like a rev counter in a car. In the '60's there was a slide rule developed for estimating pressures based on velocity. Google the phrase "Hutton and Powley 'Pressure Estimation by Chronograph' " and similar phrases. Computer programs have made the slide rule obsolete, but not irrelevant. Is there a reliable relationship between chamber pressure and muzzle velocity with all other variables being the same? The relationship can be stated as follows: P * A * t = m * delta V P = pressure in chamber/barrel A = cross sectional area of bullet t = time = barrel time = time during which the gases push on the bullet m = mass of bullet (not weight, mass) delta V = change in velocity of bullet Santa Claus | |||
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For me once you start comparing results between 2 or 20 rifles you no longer meet this requirement. When we say one of my rifles gave me 150fps more velocity than my other with exact same load. Again the need for "all other variables being the same" is no longer met. Now days we expect everything to be exact. In reloading it isn't going to happen because once you switch rifles, bullets, powders, cases etc variables are no longer the same. All the data in the world for me is a great "rule of thumb" until I apply it to my rifle I'm not sure how it will work. So I use QL, I adjust QL, I measure Head expansion, I measure velocity and as I get older I become more conservative.  As usual just my $.02 Paul K | |||
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When I work a load, I increase the powder charge in 0.5 to 1.0 gr increments while measuring velocity and examining each case for pressure signs. The case is not a "copper crusher" but it is a "brass crusher", and it will tell you when things are heating up. Before I go the range I've checked with QL to get a rough idea of how velocity and PSI MIGHT correlate. Some Words About Pressure.... There are numerous variables that would lead to an overpressure condition. One of the main considerations is the hardness of the cartridge brass in the case head region. Full Hard brass has a yield stress of about 63 KSI and the pressure would have to exceed that value to cause yielding. Many of the modern calibers typically operate at ~65 KSI, and very slight yielding occurs in the case head. Extractor dimpling and case head expansion are two of the results. Primer flattening can occur at moderate pressures if the head space is a bit on the large side. At ignition the primer backs out and then is reinserted when the high pressure occurs. The primer cups are not nearly as hard as the case head and this process will flatten the primers. To get loose primers, you have to be well above the yield stress of the brass. That would be considerably above ~63 KSI. Like I say, too many variables. Here are some words on pressure signs: 1. Primer cratering and flattening are not the best indicators of pressure. If the cartridge/chamber combination have a bit of headspace, this can make a primer look flatter. Some primers are harder than others. A weak firing pin spring or a poor fit of pin tip and hole can make a primer crater. 2. About the same time you feel the bolt handle a little harder to open, you will encounter marks on the brass, corresponding to ejector ports. This indicates for practical purposes you are a little too hot. 3. Brass starts to flow about 65,000 psi. Measuring expansion at the web is a more scientific way of doing it. Stop and back up the load a bit when the actual web of the extractor groove expands. 4. Loose primer pockets are quite a bit too much pressure. Don't confuse the area of the back of the case that expands with the thick web. 5. Maybe not the best way, but it's served me well through many thousands of rounds and dozens of chamberings. I load at the range. Take 5 pieces of brass to load over and over. Starting at a safe level slowly work up [with the same 5 cases] until primer pockets loosen, STOP. Throw this brass away. Now with 5 new pieces, drop a grain or so and load/fire 5 times. If pockets are still sound you're working right at the top-end MAX for that brass, that powder, that bullet, that temp, etc. I know of no instance where this wouldn't be safe. 6. Primer pocket loosening is the best way that I know of to catch case-head expansion - with a hand seating tool one can often feel expansion before one can measure with a caliper. Plus case heads are not round. 7. I'm not a proponent of always shooting max, but one must KNOW where it is, and some guns shoot best there. 8. Primer flattening has never been much good for me. Due to various machining differences some brands of action will experience brass failure prior to reaching this point. 9. Sticky bolt at BOTTOM of throw will be coupled with shiny deformed or scraped spots somewhere on case-head - too hot. 10. Sticky bolt at TOP of throw is another matter, could be due to tapered factory case, lack of lube on primary extraction ramp, or in the case of a custom action without ejector could be a sign of REALLY high pressure. No gun I've heard of will run this hot without very short primer pocket life. 11. This is word-for-word out of the Sinclair Precision Reloading & Shooting Handbook, a $13.00 investment and a lot of great info. Signs of excessive pressure: 1) Primers cratering severely or flowing back around the firing pin hole 2) Blown out primers 3) Gas leakage around primer, pitting on bolt face 4) Enlarged primer pocket 5) Case head expansion 6) Shortened case life 7) Ejector marks clearly visible on the case head 8) New cases are hard to extract after firing | |||
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DARN AIU it would take me 4 hrs to type that much.  Good points As usual just my $.02 Paul K | |||
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 /////////////////////////////////////////////////////////////////////////// "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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Vapodog, I don't use any calibration, it's not required, the pressure readings given are absolute, no fudge factors or reference ammo. Just because SAAMI use calibrated ammo, ie Reference Ammo, shows that pressure from one rifle is NEVER the same in another one, even when ALL tolerances are held very tightly. I'm only interested in the absolute pressure data given and use it to find MY RIFLES limits on pressure. Cheers. | |||
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416RH, What do you mean by "absolute pressure"? How is it different from intra-chamber pressure - ie., different from that measured by a copper crusher or piezo device? With a pressure trace, I assume you're measure the stretch of something glued to the outside of the chamber...correct? If so, how do you correct for different chamber wall thickness? Regards, AIU | |||
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There is no "Golden yardstick" of what constitutes "safe pressure levels" for multiple weapons. And any figure that is supposed to be etched in stone as the max for this "type" of action or that one is an arbitrary number and even with a strain gage the basic rules of watching for pressure signs still applies. The thread began with talk of having a "fast barrel" and thinking that it is OK due to powder quantity or ?? What about a slow barrel? I chronographed an old 06 that shot considerably slower than another 06 AND well below what reloading manuals indicated velocity should be. Does that mean I am free to juice it up some more?? I dont think so.. I re barreled that rifle and gained nearly 200 fs with the same load! If I would have kept pushing until it reached published ballistics the chamber pressure would have been through the roof. I DO use my chronograph as a tool to help place me within safe loading limits. But as each rifle is different, it is also advisable to consider all other available signs. Including references like manuals and quickload. The more information the better! It is no great mystery to reloaders that two identical rifles can "max out" at different velocities. And I believe that the reasons for this are basically more intricate than anyone here is alluding to. | |||
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