The Accurate Reloading Forums THE ACCURATE RELOADING.COM FORUMS Guns, Politics, Gunsmithing & Reloading Reloading Using a Chronograph as a Pressure Guide...................Go | New | Find | Notify | Tools | Reply | |
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I'm starting this thread to discuss how an average reloader can use a Chronograph as a Pressure Guide. To start with I hope that anyone reading this thread will keep a few things in mind. I hope everyone will do some research and do some reading for themselves and maybe bring in some good references for or against the ideas here. Personal insults are usually a sign of someone who has lost an arguement and is a sore loser. We all learn more from test data, authoritative references, engineering data and the like than from assumptions, insults and name calling. With any luck some of our distinguished Forum members like Ken Oehler might even chime in. OK here's my point. An accurate chronograph WITHIN LIMITATIONS, can be the best indicator of pressure an average reloader can own. As an example if you find a load in one of the new pressure tested manuals that says for the 300xyz if you load 75grs of Powder X for a 180gr bullet they get 60,000psi and 3100fps in a 24" barrel. If you load the same 75grs of powder X in a 24" barrel with a 180gr bullet and your chronograph shows the load at 3100fps you are probably near 60,000psi. Now if you are loading the same powder and bullet and are getting 3300fps you are at HIGHER PRESSURE than 60,000psi! The main point is that if you are getting 200fps faster than the reloading manuals with the SAME COMPONENTS you are at HIGHER PRESSURE! There isn't such a thing as a "fast barrel" that will magically acheive 200fps faster in the same bullet length as everyone else without signifigantly higher pressure. There are factors such as a rough bore, long throat, oversize chamber etc. than will make a given barrel not be able to acheive as high of velocity as other barrels at the same pressures but there aren't Magic barrels that will acheive higher velocities than other barrels of the same type. Polygonal barrels can acheive higher velocities at the same pressures and some other types of rifling but YOUR Polygonal rifled barrel won't acheive higher velocities than other polygonal barrels of the same length without HIGHER PRESSURES. Now again, you have to compare Apples to Apples as closely as possible but you CAN use the Chronograph to help keep your loads above maximum pressures. If your reloads are faster with a given bullet than any of the manuals are able to acheive you are running Higher pressures. Sticky Bolt lift, flattened primers and the like can be very unreliable indicators of higher pressures. You can take a blueprinted action with a properly fitted custom barrel and shoot loads waaayyy over normal limits before you start getting sticky bolt lift. You can have lugs with poor engagement that will stick with loads that within Pressure limits. Other factors other than high pressure can cause flattened or peirced primers. Chronographed velocity is the best overall indicator of safe pressures, if you velocity is way high - so are your pressures. Unfortunately Oehler isn't currently making the model 43 which can measure RELATIVE pressure of a given rifle. It gives a readout in PSI. This is not however absolute pressure (I think it's the model 83 you need for that). The 43 will give you a pressure reading from round to round but not necessarily the true absolute pressure. For that SAAMI distributes test rounds that are loaded to a calibrated pressure level. You shoot the calibrated rounds in your system to calibrate it. These are NOT available to the average reloaded. My best suggestion is to reference as many reloading manuals as possible for a given load. Make a chart of the maximum loads for a given powder and bullet weight and see how close the different manuals are. For example if 5 of 8 manuals list 76grs of RL-22 for 180gr bullets as their maximum loads and 1 lists 78grs and another lists 74grs, 76grs is probably the best figure for a maximum load. Make an average of velocities given in the 5 manauals listing 76grs and that is probably the velocity that you can acheive in YOUR rifle without exceeding maximum pressures. So in summary: There aren't magic "fast barrels" that allow you to get 200-300fps faster in the same barrel length that the manuals list. There are things that can make your barrel not acheive the same top velocities as other barrels of the same length without resorting to higher pressure loads. A Chronograph can be the best indicator for when your loads are getting to hot. Load safe! If you really need higher velocity than you are getting with a given bullet, buy a bigger gun! Don't overload rounds than what they are designed for. OK, Flame away. Everyone has their opinions but opinions supported by facts and data are far more valued than groundless ones  ........................................  DJ....Remember that this is all supposed to be for fun!.................. | ||
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How does a chronograph know when you have a fast or slow lot of powder? | |||
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The fastest lot of any powder isn't going to let you acheive 200-300fps faster velocities. For example it doesn't matter what lot of RL-22 you have, you can't acheive 3400fps with 180gr bullets in a 24" 300 WIN mag without high pressures.................................DJ ....Remember that this is all supposed to be for fun!.................. | |||
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You are stuck on velocity. Talk about pressure. How do you know you are not developing high pressures with a much faster lot of powder? Normal velocity but excessive pressure. | |||
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I think you meant to state ......to help keep your loads below maximum pressures. In general, I tend to agree and use my Oehler chrony as a tool to keep me away from high pressure loads. | |||
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This would fall under the question being asked. Muzzle velocity is a result of mean pressure, so as long as the mean pressure is the same the velocity should be similar. But that's what SR4759 is getting at, right? There is a problem I have come across with reloading manuals in that they do not always specify the lot No. of powders and supplyers do not always indicate the lot No. on the containers. I have come across conflicting load data from the same supplyer for the 'same' powder! The bullet used was not indicated either. Regards 303Guy | |||
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In the example: If one tests his load and finds he is actually achieving the 3,100 FPS with the 180 grain bullet and the powder company notes that their tests using the powder he is using they recorded 60,000 PSI with that load of "X" grains (same as the reloader is using) then the reloader can assume only that he might be incurring pressures of 60,000 PSI. This does not mean that if the reloader is not achieving the 3,100 that he can add powder until he does! Nor does it mean the reloader can ignore pressure signs working up to that load as his actual pressures may be significantly higher than the tested data. Nor does it mean that the reloader does not have to "work up" to the data tested. It's not at all bad, once, and if, he has successfully achieved the same results as the tested data that the reloader say to himself "well, I could be about 60,000 PSI so I think I'll stop here." This is a decision based on implied data. To an extent I agree that one can use the chronograph as a pressure indicator but one must always remember the context in which the information is used and never jump to the conclusion that pressure "X" yields "Y" results. This is a formula for potential trouble. Incidently, I'm not a believer in the urban legand of "fast barrel". It's a term used to explain things we do not understand and have not measured! | |||
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Along the same lines, I had a rather interesting experience (to me) with a particular load. This load produced fair velocity and reasonable pressure but heated the barrel and muffler enormously. Increasing the charge by a small amount resulted in a far cooler barrel and obviously higher velocity (not measured). There was little difference in pressure indications on the case and primer. The point being that things are happening inside the case and bore that are somewhat less than straight forward! I wouldn't mind knowing the velocities I get but I think that, like the dog that chases the bus, I wouldn't know what to do with it when I get it!  There was a time when I could measure velocity and found it interesting, particularly since I was right there where I thought I should be but it bothered me that I wasn't higher and I even tried to go up in velocity but backed off again for pressure reasons and anyway, both rifles shot fine like they were and the one recoiled too much anyway! Regards 303Guy | |||
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We tested 5 Mannlicher Luxus rifles, all brand new, in 270 Winchester, using Normal 150 grain ammoo, from the same batch. Velocity difference between the slowest rifle and fastes was 150 fps!!? | |||
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Saeed, what in your opinion, accounts for this? | |||
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I also use my chronograph to infer pressure limits. My method is similar to yours in that I use my reloading manuals powder charge weight for a specific bullet as a pressure/velocity guide. When developing a new load I load in 0.5 grain strings, starting below the MAX book pressure and going up to the MAX book pressure (sometimes I even go a little bit above the given MAX book pressure). I then shoot these loads over the chronograph (starting w/ the lowest charge weight load) and record the velocity. What I'm looking for is a linear relationship between the velocity for the increased charge weight (which in my case is 0.5 grains). What I have found is this, in general, when operating below the RED ZONE or Excessive Pressure this linear velocity increase "tends" to hold up, but when I get to a charge weight where I'm getting into high pressure, this linear relationship starts breaking down. For example, say each 0.5 grain in powder is giving me a 20-25 fps increase in measured velocity - if the next higher charge weight load gives me a 80fps increase I infer that I'm now getting into the dangerous area, becaue I have lost that linear trend and things are becoming erratic and I will stop here and not go any higher. I have also found that different "makes" of bullets with the same weight behave differently, so I will not shoot a Nosler Partition load of xx.x grains, that I have worked up to (with the above method) with a different bullet. I go through the above process for each different bullet. | |||
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And if the reference barrel happened to have the rough bore then all smooth bores would have a higher velocity? Like Saeed said I have had twin rifles built as close to the same as possible with velocity differences of 150-200FPS with identical loads. If we knew the reference sample had the best barrel out there then matching its velocity at a give charge would be the best we could hope for? Heck many of the manuals list factory rifles as the base line. Read the manuals many simply use an extrapolation of velocity gains to set limits. I think my Hornady book even mentioned using the same line slope for all IMR powders. So how do you even know a max velocity and charge limit was actually shot or estimated? To me a Chrony is just another piece of info. Since a majority of my loading is my own wildcats I do track velocity gain per powder increase to watch for a huge out of line jump. But it is only one of several items I watch. As usual just my $.02 Paul K | |||
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I think a chrono helps to understand pressure vs vel. but it's impossible to determine safe pressures by vel. alone. As already stated, barrels & chambers vary quite a lot. You can have a load exhibit high pressure signs & vel. be actually lower than a previous load (ie, 61gr shows 2800fps, 62gr shows sticky bolt, flattened primer & vel. of only 2810fps). Where i find the chrono valuable is when changing components or OAL. If all things are the same & youchange OAL & get higher vel. you are likely getting higher pressure, same for primers. LIFE IS NOT A SPECTATOR'S SPORT! | |||
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Very well said! | |||
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A chronograph can only measure velocity - we might infer pressure from its readings, more powder more pressure = more velocity. However, if I load bullseye in a 308 behind a 150g bullet, the chronograph will encourage me to keep filling the case until I need a new rifle! A few years ago Border-barrels for a short time produced the “Kolbe P-Max model CP-1” this used an accelerometer bonded to either a 1" or 30mm clamp which attached to the telescopic sight - and converted this into a maximum bullet base pressure. Unfortunately if failed commercially, but this is perhaps a more reliable way or measuring pressure. | |||
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Great thread Gentlemen. But the discussion has lead me to come to the conclusion that the best way to determine if a load has excessive pressure is by conventional means.....flattened primers, sticky bolt lift, etc. It seems that there is plenty of disagreement on the published data velocity vrs. actual velocity issue as being an indicator of an over-pressured load. Am I correct in my conclusion? | |||
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RCA, I guess that I would answer your question with a question? I have a 140 grain 6.5 bullet that was chronographed at 2600 FPS. What pressure did the load produce? | |||
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I realize that an under-velocitied load will create an over-pressured situation as well......... Right? Also, I guess it is cartridge dependent too? | |||
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I like your methodology. Some here I think are not comprehending all of the conditions here necessary to make an educated estimate of what pressure you are at. Asking what pressure a 6.5 caliber bullet at 2600fps is at is ridiculous. Now if you added necessary information such as the Vitavouhri 2nd edition manual on pages 115 and 116 using a 26 1/2" 1/8.5" twist barrel lists with 46.9grs of N165 powder and a 140gr Sierra bullet a velocity of 2626fps and a pressure of 46,700psi. Then ask something like "In my 93 Mauser with a 26 1/2 1/8.5twist barrel 26.9grs of N165 and a 140gr Sierra bullet gives me a average velocity of 2600fps what is my pressure" - well it's probably pretty close to 46,700psi! You must have enough information to make the estimation and not pull it out of thin air. As far as the 5 rifles that showed 150fps difference was this the differences in average velocities for several shots? Was this the Maximum difference high to low of all shots? If you wouldn't mind having the raw data would be interesting to add to the discussion. I would think that the differences would be from the normal high velocity for a 150gr bullet in the 270 to lower, rather than the lowest velocity being normal max velocities to 150fps faster than normal - but I would like to see the raw data. As mentioned there are things that make an barrel slower than normal but there aren't magic fast barrels that are somehow a couple hundred feet per second faster than normal barrels at the same pressure. That being said it wouldn't be that unusual for the Norma Ammo to be hotter than most. I had a Weatherby MK V lightweight 338-06 that would shoot Norma Factory 210gr partitions 150-200fps faster than any load that I could find in a book. I also had the Primers FALL OUT of the FACTORY AMMO after firing! No doubt that load in my rifle was shooting at higher than normal Pressures! I really don't think that there is a 150-200fps difference between lots of a given powder. Maybe some of you out there have documented such but I haven't seen it. If you have please report it to us - it would be some new information to me. I did see about a 50-75fps difference between early lots of RL-22 and later lots. The early lots seemed to be a little warmer in some calibers. A good buddy of mine did a temperature sensitivity test with one of the later lots of RL-22 and in his tests (PRDATOR) RL-22 was less temperature sensative than a couple of the Hogden Extreme powders (IIRC, you might do a search and reread his post on it). I wonder if they might have slightly changed the formulation of RL-22 to make it less temperature sensitive and this slowed it down a bit in high temperatures and this accounted for the 50-75fps differences. It would be interesting to hear what actual chronographed differences in lots of powder, shot at the same temperatures and conditions that other posters have seen. As we've seen there are differences between rifles shooting the same ammo. Saeed's test with the Steyr's seems to be on the wide side of variation between the same model but it's not that unusual to see it between different rifles of the same caliber. I have a few 270 WSM's. With the same load 2 of the Kimbers reach nearly the same velocity. With the load used in the Kimbers my Sako that has the same length barrel the Kimber loads are 150fps or so slower. The Sako has a particularly long throat for a WSM (WSM's usually have tight throats) and I think that that accounts for a lot of the velocity difference. In 300 WSM the same thing happened, the long throated Sako Finnlite shoots the same loads slower than the Kimber 300 WSM, though not to the same amount as the 270 WSM's. Naturally I don't load the Sako's with the same powder to the same velocity as the Kimbers. I've also seen where my rifle acheived normal maximum velocities with several grains LESS powder than listed in the manuals. My Model 10 Dakota 7 Dakota gets max velocities with both 140 and 160gr bullets with 4-5grs of the same powder listed in the Hornady and Dakota data. With this rifle I shoot loads just a little back of the same loads that acheived the normal maximum velocities. I never shot loads with the listed max powder charges because I new that pushing them even faster would increase pressure even more. It shoots great 50-75fps below normal max velocities using several fewer grains of powder and my cases last a long time. This was one the best examples to me personally of using the Chronograph to limit the maximum loads for a given rifle. One of these days I should get around to making a chamber cast and slugging the bore to see if it has tight throat and bore. I think that it might be a tight bore, a while back some other posters has noticed a few bore size differences with 7mm barrels and this could account for my rifle shooting faster with less powder (among other possibilities). So again NEVER ASSUME that your chronograph is going to give you the exact absolute pressure (even a Oehler 43 with strain guages). But it can give you a good idea of where your maximum loads should stop, and if your velocities are closely matching a pressure tested manuals levels with the same components, you are likely reasonably closely matching their pressure levels also. ....Remember that this is all supposed to be for fun!.................. | |||
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....Remember that this is all supposed to be for fun!.................. | |||
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....Remember that this is all supposed to be for fun!.................. | |||
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"DO NOT EXCEED SPEEDS"..... exactly!.... if your chrono is saying you have reached a specified "max velocity" as published in the manual, you can assume you are at or very close to max pressure for that cartridge. going beyond that throws the chrono out the window as far as a comparator for pressures..... i would add thankfully, few guns will reach published maxes before showing pressure signs. | |||
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If your chronograph readings approach max book velocity, you can assume that you have reached, or have already exceeded, max pressure. "Identical" barrels don't exist. Just because they came from the same maker, drilled with the same drill, chambered with the same reamer, and measure identical, they probably will not fire the same pressure and velocity. You can assume that if you get a higher velocity, it came at the cost of higher pressure. Lower velocity does not guarantee lower pressure. Reference ammo is used to determine the correction factor relating a particular barrel to the mythical average test barrel. It is not an absolute pressure reference. That's just the way I see it. 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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Merlinron, I guess that it could be that I have several freinds with lots of rifles but I've seen quite a few rifles that were being loaded well beyond recommended limits and didn't show pressure signs. I had 2 freinds in particular that beleived in the "fast barrel" theory, the one that blew up a rifle no longer beleives so and is a careful reloader now that keeps excellent records. The other refused to beleive the bulged chamber had anything to do with his loads several grains over the limit and as far as I know still loads that way. I tend to shoot a few benches away from the second one. I really think that well lapped and mated bolt lugs are enough to fool "sticky bolt lift" into not showing until pressure levels are well above where they should be. I also have seen an oily chamber cause sticky bolt lift with normal loads. I really think that sticky bolt lift is a very unreliable pressure indicator...............................DJ ....Remember that this is all supposed to be for fun!.................. | |||
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MR. Oehler, Thank you VERY much for responding to this thread. I stand corrected about the reference ammo and absolute pressure reference. I consider what you have to say as the most authoritative word on this subject. Please correct whatever I've said on the subject when needed................................DJ ....Remember that this is all supposed to be for fun!.................. | |||
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If they don't really know what caused the problem you don't really know what caused the problem. Most reloaders don't know and if they did they wouldn't admit that an inanimate object was destroyed by their own lack of knowledge and attention to detail. | |||
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Hmmm.....maybe try one of these if you need reliable data ...   | |||
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Well I guess if you don't have strain gauges attatched to the rifle and it blows up in a labratory environment maybe you can be overly pedantic and say that you don't "know" what happened in a particular case but on the other hand evidence can lead to a pretty good conclusion. In the second case of the rifle with a bulged chamber there's pretty strong evidence of what probably happened. I bought the rifle from the freind with it he sent 4 or 5 different loads he had been shooting in the rifle. They were SEVERAL grains over the listed maximums in several different manuals. Of course I didn't shoot them but pulled the bullets and dumped the rest. I shot the rifle for a year or two and it did NOT have a bulged chamber. I liked the rifle but needed money for a hunting lease and sold the rifle back to the friend. A couple of years later we were working on another trade deal and I asked about the same rifle, since the time I owned it it somehow had aquired a bulged chamber and he said that he had to send it off to be rechambered for a caliber that cleaned up the bulge. Needless to say the rifle had lost it's appeal to me. It seems pretty obvious that the rifle (a Winchester Featherweight) had returned to a diet of high pressure loads that caused the bulge in the chamber. I guess it could have been oil in the chamber or something but I doubt it ( sorry couldn't resist).Regardless of what you think happened in the two different rifles. I think that Mr. Oehlers words are the best, most authoritative possible: "If your chronograph readings approach max book velocity, you can assume that you have reached, or have already exceeded, max pressure." Thanks again, Mr. Oehler................................DJ ....Remember that this is all supposed to be for fun!.................. | |||
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You can assume anything you like. I wouldn't make that assumption EVER ..!!! | |||
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I ask because I don't know the honest answer. When a BOOK or call it a "pressure book" lists a max load and velocity what are they using for the pressure limit? Saami? Brass expansion? Reason I ask is for cases of the same design with huge differences in pressure Limits. The 7x57 and 257 around 54000 the 6mm at 65000. Why the 243 at 60000 and 6mm at 65000. I based my wildcats on a 280 with limits of 60000 but I could just as easy use 270 at 65000. I kept pushing the issue with Loadtech to allow the their program would not allow my wildcats to calculate to 65000. I pushed so hard they told me they would drop my cases from their data base if I wasn't happy. As usual just my $.02 Paul K | |||
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Ramrod, Most of the manuals use SAAMI pressure limits but some like the Vitavourhi manual will also list the CIP ones. I think your confusion is why would near identical cases such as the 270 and 280 have different SAAMI pressure limits. In the case of the 280 it's because when it first came out it was chambered for an Autoloader and they downloaded it to work without too much wear on the autoloaders mechanism. In a Bolt Action rifle there's no reason a 280 case wouldn't withstand the same pressure as a 270 case. Look in a manual and you'll notice that the 280 has lower max powder charges for the same weight bullets as a 270, if the pressure levels were the same the 280 would have slightly higher max charges due to the slightly increased bore diameter. There shouldn't be any reason a 280 shouldn't shoot a 140 or 150gr bullet just as fast as a 270 will when loading them to the same pressure levels, in fact the 280 should be slightly faster. Some rounds like the 9,3x62 have pretty low pressure limits since there are still a lot of older weaker guns chambered for them. Loaded to the same pressures as modern rounds they will acheive higher velocities than you can acheive than with the data supporting lower pressures. Oh, and yes a Krieger test barrel would be an excellent starting point for real test data. Unfortunately though a $350 test barrel might be in the price range of a normal reloader the equipment required to use a test barrel isn't.......................................DJ ....Remember that this is all supposed to be for fun!.................. | |||
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I'm well aware why the 280 was limited to 60000. Or a 7x57 to 54000. My point is if a "pressure book" uses 60000 as the limit for a 280 or 54000 for a 7x57 and I as a reloader using new brass bolt action rifles etc and choose to load to 65000 then what is the velocity/load from the book really telling me? Why should I stop at the velocity listed in the book in these two cases as an example? What is your procedure telling me in these cases?  As to your earlier question I used pressure equipment including Ken's set up in the testing of my first several wildcats. My smith also had a relative that worked for one of the big bullet houses that also did some testing for me. My own wildcats were cut with the same two reamers sized for Norma brass. 280 and above and 6mm to 6.5. I bought over 1000 280 cases from the same lot and used it in all my development. I found that my Norma cases would start showing head expansion at a very consistant and acceptable pressure (at least as read by my equipment). In later work I simply loaded to that point and set that as max for a given powder and bullet. I spent a lot of time and $$ testing my family of cases from the early 80s to 1999. Specially taking the same barrel from 280-280AI-7JRS and my 280PDK documenting gains at as equal a pressure as I could measure. As well as testing various AI gains at what I measured as equal pressure. Then I met John Wooters and after sharing some of my PDK data he said hey that sounds a lot like Rocky Gibbs work. After reading up on Rocky having my buddy lose some of my data by driving off with my book on his trunk lid. Getting divorced and having her toss brass and data as well as delete computer files I gave up. As usual just my $.02 Paul K | |||
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Sorry to hear that! Regards 303Guy | |||
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I have no idea what is causing this. But, I have a Remington 300 Ultra mag which has higher velocity than a 30-378 Weatherby!!? Dr. Oehler mentioned pressure, which brings up a point I have been taken to task about. We developed loads for our 404 Jeffery, built on a Sako 75 action. Getting velocities higher than factory loadings. We have shot the same brass cases several times, and neither they nor the rifle showed any sign of excessive pressure. But, some members insisted that we are playing a dangerous game by using loads which are of much higher pressure than acceptable. This brings me to the point. What is an acceptable pressure IN ANY PARTICULR rifle? On the other end of the scale. I have had European built rifles that showed signs of excessive pressure with both factory ammo and minimum loaded reloads. Where does oen drwa the line? Here in our range we stop as soon as we encounter stiff bolt lift, flattened primers etc. | |||
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I'm amazed. During the past year there have been knock down drag out forum fights (here and elsewhere) about how pressure relates to velocity and it would appear that the numbers of reloaders who acknowledge that velocity is not a reliable indicator of excess pressure has risen dramatically. | |||
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Thank you for this thread. The information contained here and my subsequent research has transformed me into a safer, much more aware reloader! The reason folks rifles have blown up seems to be due to excessive head space which can be the result of firing loads that have too much pressure. Research has shown me that these loads may not have displayed any visible signs of over-pressure. Constant hammering of the bolt face with over-pressured loads. I used to be a "velocity guy" until now. Mark it down. | |||
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Ramrod, It's unfortunate that you lost all of your data! If you were pressure testing with an Oehler 43 and keeping careful notes of powders and bullets I'd probably been happy to use your data if I had a rifle in your Wildcat calibers. It sounds like you had a good thing going and were careful not to exceed 65k psi with them. I use a few loads that are above the std. low pressure limit for the 9,3x62. They are pressure tested to be below 60k psi but are above the std CIP loads found in manuals, SAAMI doesn't have a std for 9,3x62 but the for the rifles I shoot them in 60K psi is perfectly safe. I could probably just as safely load them to 65K PSI with the high quality brass and newly manufactured rifles I shoot them in but I don't find it necessary to push them to the edge. I do wish that Mr. Oehler would produce the Model 43 again.............................DJ ....Remember that this is all supposed to be for fun!.................. | |||
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I'm always glad to see people recognize Reality instead of incorrect, totally wrong, wishful thinking. ----- I've had Fast Barrels, Slow Barrels and Barrels inbetween. All a person has to do is gather a few rifles chambered for the same Cartridge, use the same ammo in each and it becomes obvious. Just as Saeed noted with the 150fps, but it could be even higher. The previous 7mmRemMag I had was made with a Fast Barrel. It was due to the Bore being slightly larger than other 7mm rifles. My current 7mmRemMag has a Slow Barrel, which is actually a bit tighter than other 7mm barrels. And there are Chamber dimensional differences between them also. All of which adds up to some being Fast and some being Slow - just more Reality. ----- Count me, as usual, among the folks who understand it is completely impossible to tell what the Pressure of a Cartridge is from looking at a Velocity. Too many Variables prevent it from happening, regardless of how well your individual Cartridge components match what is used in a Manual or Manufacturers Web Site. | |||
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Hot Core, you are deceiving yourself if you think that your "Fast Barrel" is going to acheive faster than normal velocities without higher pressures. Yes there is no doubt that some barrels are slower than others. As a general example there are several loads that will allow a 300 Win Mag to shoot 180gr bullets to around 3100fps give or take. Some barrels with longer throats, fat chambers, rough bores etc. might not be able to acheive much over 3000fps without excessive pressures. If you call the 3100fps barrels fast barrels and 3000fps barrels slow barrels OK. But if you think that there are 24" barrels that will allow you to shoot 180gr bullets in a 300 Win Mag at 3250fps you are dead wrong. You don't need to listen to me but you should listen to one of the top experts alive in the feild - Ken Oehler. " If your chronograph readings approach max book velocity, you can assume that you have reached, or have already exceeded, max pressure. " Identical" barrels don't exist. Just because they came from the same maker, drilled with the same drill, chambered with the same reamer, and measure identical, they probably will not fire the same pressure and velocity. You can assume that if you get a higher velocity, it came at the cost of higher pressure. ". There is NO SUCH THING as barrels that will allow you to signifigantly exceed Pressure tested reloading manual velocities without exceeding normal pressures..........................................DJ ....Remember that this is all supposed to be for fun!.................. | |||
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