how to calculate pressure?
- Thread starter legi0n
- Start date
Cartridge : .38 Special (SAAMI)
Bullet : .357, 158, GECO FMJ Sp
Cartridge O.A.L. L6: 1.475 inch or 37.47 mm
Barrel Length : 6.0 inch or 152.4 mm
Powder : Hodgdon TiteGroup 4.5grns
28512 PSI with the bullet listed above.
Do you have a specific bullet in mind?
Bullet : .357, 158, GECO FMJ Sp
Cartridge O.A.L. L6: 1.475 inch or 37.47 mm
Barrel Length : 6.0 inch or 152.4 mm
Powder : Hodgdon TiteGroup 4.5grns
28512 PSI with the bullet listed above.
Do you have a specific bullet in mind?
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thanks CyaN1de,
I just want to make sure I'm not putting too much stress on the cylinder while playing in the gray area between 38spl P+ and 357magnum
How do you crunch the numbers? Any software you'd recommend?
Quickload is what I used and it is showing that load is grossly over pressure. I don't know what max pressure for these should be so take it for what it's worth.
I don't mess with handgun cartridges yet so I only plugged in the info you had supplied. Actual pressures may be higher or lower and may or may not be safe in your particular firearm.
thanks again
My 357 magnum should be fine with it (SAAMI spec 35000PSI). Or else I'll need a new one
I have used quickload for the last 4 years, and have measured actual pressures using a strain gauge on one of my rifles.
I find the quickload values to be good, and if anything they overestimate pressure and as a result velocity. I think this is a purposeful overestimate for the sake of safety. Generally I never load in what quickload indicates as a 'Red zone'
I find the quickload values to be good, and if anything they overestimate pressure and as a result velocity. I think this is a purposeful overestimate for the sake of safety. Generally I never load in what quickload indicates as a 'Red zone'
- Location
- Somewhere on the Hudson Bay Coast
While it does not give you a pressure number, if you work up a load in equal increments, and shoot each across a chronograph, when the velocity increase plateaus, you are close to maximum pressure, and the subsequent increase will probably result in sticky extraction.
When working up a 195 gr hard cast load with H-110 for my .357 I observed the following:
12.0 grs - 1000 fps
12.5 grs - 1076 fps
13.0 grs - 1116 fps
13.5 grs - 1128 fps
The difference in velocity between the 13.0 and the 13.5 gr loads was only 12 fps, and I settled on 13.0 grs as my working load.
When working up a 195 gr hard cast load with H-110 for my .357 I observed the following:
12.0 grs - 1000 fps
12.5 grs - 1076 fps
13.0 grs - 1116 fps
13.5 grs - 1128 fps
The difference in velocity between the 13.0 and the 13.5 gr loads was only 12 fps, and I settled on 13.0 grs as my working load.
Just to point out that the velocity "plateau" you mention is not necessarily maximum pressure. It could also be the limitation of the % of powder burn depending on barrel length. Adding more powder WILL increase pressure but because it won't all burn, within the barrel, the velocity doesn't increase as much.
Just to point if anyone is duplicating the above loads, that they MIGHT be very hot depending on OAL. At standard OAL the 13 gr load is likely above proof pressure. Increasing OAL by 0.1" substantially reduces pressures.
- Location
- Somewhere on the Hudson Bay Coast
I kind of doubt that. Proof loads are typically well beyond the point that sticky ejection would be experienced, (up to 25% above the maximum pressure) and in none of the loads I've mentioned was sticky extraction experienced. All my my loads were conventionally loaded with the case crimped in the crimping groove of the bullet, and thus loaded were within the acceptable length to function in my revolver.
Every cartridge will have an efficiency range with a given combination of components. Once that range has been exceeded, the pressure will spike and velocity will show a minimum increase. But you are correct in one respect, no one should assume the above loads are safe until they have worked them up in their own guns. I worked these loads up for my M-27, and in that gun they are safe.
As for maximum pressure, the velocity plateau simply warns you that the maximum safe pressure is close at hand. The next increment will almost always result in sticky extraction or leave ejector marks on the case head in a rifle load. The technique is safe to use with modern cases in modern firearms. Naturally you could run into some problems if you attempted to use this technique with modern .45/70 cases in an old Trapdoor Springfield.
This is the technique that I have been using for working up all my metallic cartridge loads since I found out about it in the Sierra newsletter some years ago. It has saved me from working up loads until I have dangerous pressure signals, such as ejector marks or sticky extraction. It also gives me a point to work away from if I am interested in tweaking a load for accuracy.
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Boomer,
Just letting you know what I found when I ran your numbers through Quickload and also compared results to the Hodgdons website.
The 13 gr load, if loaded to typical LOA, was well beyond SAAMI specs. SAAMI proof pressures for high pressure centerfire handgun cartridges are between 1.30 and 1.40 working pressure. 357 Mag has a SAAMI working pressure of 35,000 psi so min proof is 45,000 psi. And Quickload calculated above this pressure.
At 45,000 psi, you are not going to have sticky ejection.
The QuickLoad calcs also correspond well to the Hodgdsons website that lists a 180gr bullet (jacketed) with 13.5gr H110 at 39,100 psi. Jacketed bullet pressure compared to lead pressures are only a few thousand psi higher for the same load. (but lead velocity is much higher)
See post above by roberti11 where he verified that QuickLoad values are generally good.
Just letting you know what I found when I ran your numbers through Quickload and also compared results to the Hodgdons website.
The 13 gr load, if loaded to typical LOA, was well beyond SAAMI specs. SAAMI proof pressures for high pressure centerfire handgun cartridges are between 1.30 and 1.40 working pressure. 357 Mag has a SAAMI working pressure of 35,000 psi so min proof is 45,000 psi. And Quickload calculated above this pressure.
At 45,000 psi, you are not going to have sticky ejection.
The QuickLoad calcs also correspond well to the Hodgdsons website that lists a 180gr bullet (jacketed) with 13.5gr H110 at 39,100 psi. Jacketed bullet pressure compared to lead pressures are only a few thousand psi higher for the same load. (but lead velocity is much higher)
See post above by roberti11 where he verified that QuickLoad values are generally good.
- Location
- Somewhere on the Hudson Bay Coast
SandRoad,
Revolvers are difficult to generate computerized pressure data for due to variations in the cylinder gap. This is one reason that there are instances where a 4" revolver can produce higher velocity than a 6". A load that is safe in my .44 SBH produces sticky extraction in my Vaquaro. Despite the best efforts of SAAMI, not every gun complies. We have a number of rifles that predate those standards (1926). There are several different throat configurations in revolvers that can effect pressure, despite the fact that the guns are chambered alike. Pressure is also effected by the distance that the bullet must jump to the lands and the rate of twist of a given barrel, handgun or rifle. The length of the bullet's bearing surface effects pressure as does the hardness of the bullet. Not all cast bullets of the same weight produce equal pressure due to the number of grease grooves and their size. Unless you work up the load for your own gun, you are guessing, and using QuickLoad without a baseline for your particular gun is just high tech guessing.
Revolvers are difficult to generate computerized pressure data for due to variations in the cylinder gap. This is one reason that there are instances where a 4" revolver can produce higher velocity than a 6". A load that is safe in my .44 SBH produces sticky extraction in my Vaquaro. Despite the best efforts of SAAMI, not every gun complies. We have a number of rifles that predate those standards (1926). There are several different throat configurations in revolvers that can effect pressure, despite the fact that the guns are chambered alike. Pressure is also effected by the distance that the bullet must jump to the lands and the rate of twist of a given barrel, handgun or rifle. The length of the bullet's bearing surface effects pressure as does the hardness of the bullet. Not all cast bullets of the same weight produce equal pressure due to the number of grease grooves and their size. Unless you work up the load for your own gun, you are guessing, and using QuickLoad without a baseline for your particular gun is just high tech guessing.
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Boomer, sorry but many of your statements are not quite right. In a couple cases you are interchanging effects of peak pressure, pressure as a function of time (distance) and velocity.
The 357 mag load in this example generates peak pressure within LESS than 1/4 inch of bullet movement. That means the base of the bullet has not even cleared the case so cylinder gap plays no part in PEAK pressure. Yes, throat configuration does have an effect, but only on the order of a couple thousand PSI and it depends if the bullet has actually engaged the throat at the time of peak pressure.
The length of the bearing surface, hardness, etc, has almost no bearing on PEAK pressure, but they DO have a bearing on velocity. (plus other factors)
In this case QuickLoad will NOT give a good indication of velocity because of the factors you mention. But the PEAK pressure is going to be pretty good (given case volume remaining with the bullet seated) because it occurs so soon after ignition.
Yes, working up loads is necessary. But if a person is truly knowledgeable about how computer simulations/modelling works, and that means ALL the background, (and I am not just saying QucikLoad), then results are surprisingly good. Consider that almost all aircraft are now built and "tested" using only computer modelling as to how far computer simulations have evolved.
The 357 mag load in this example generates peak pressure within LESS than 1/4 inch of bullet movement. That means the base of the bullet has not even cleared the case so cylinder gap plays no part in PEAK pressure. Yes, throat configuration does have an effect, but only on the order of a couple thousand PSI and it depends if the bullet has actually engaged the throat at the time of peak pressure.
The length of the bearing surface, hardness, etc, has almost no bearing on PEAK pressure, but they DO have a bearing on velocity. (plus other factors)
In this case QuickLoad will NOT give a good indication of velocity because of the factors you mention. But the PEAK pressure is going to be pretty good (given case volume remaining with the bullet seated) because it occurs so soon after ignition.
Yes, working up loads is necessary. But if a person is truly knowledgeable about how computer simulations/modelling works, and that means ALL the background, (and I am not just saying QucikLoad), then results are surprisingly good. Consider that almost all aircraft are now built and "tested" using only computer modelling as to how far computer simulations have evolved.
- Location
- Somewhere on the Hudson Bay Coast
I don't think you've got your facts straight. If you look at any loading manual you will see that cast bullet loads produce less pressure than the same loads with jacketed bullets of equal weight. This relates to the hardness of the bullet and its bearing surface. If what you say is true, then the same loads fired in a pair of .44 magnum revolvers from the same manufacturer, supposedly both built with SAAMI tolerances, should have been fine, yet one produced sticky extraction. As I said earlier, this is the case with my .44's, and the load comes right from the Hodgdon manual, 20.0 grs of H-110 with a 325 gr hard cast bullet. I did not attempt in either gun what Hodgdon listed as the maximum load, which if I recall correctly was 22.0 grs.
As for computer modeling, when Lockheed designs an aircraft on a computer, or GM a car, or Harley Davidson a motorcycle, the designer controls every aspect of the design parameter. When loads for firearms are being run through a computer program, the program has no way to take into account the actual internal dimensions of a specific firearm, so I assume it takes the center of the SAAMI specification. The trouble is that every firearm is an individual, and some firearms are custom made outside of the SAAMI spec. Consider my .308 target rifle. It has a 28" 1:8 barrel, and 50 grs of Win 760 drives a 200 gr MK just under 2700 fps with no high pressure signs. That's about 300 fps above the maximum velocity and 3.5 grs over the maximum load in the Sierra manual. Now, how did I do that? I'll give you a hint, it is not an AI chamber. I bet QuickLoad calls that over 100K for pressure, which of course is not possible with a M-700 action. All you have to do is change one aspect of the internal dimension of the chamber, and the load data in the manual or the estimation by QuickLoad ceases to be relevant.
The choice of brass also has an effect on pressure. When a load cycles fine in one make of brass but the same load sticks in another make of brass, it is because some brass has less volume than average. Again, to load in a safe manner, you have to work up your load from below what the manuals or the computer programs call safe maximum.
In some cases, like with my .308, you can safely exceed the maximum book load, in other cases, like my .44 Vaquaro, the maximum book value produces an overload. Yesterday I was working up a load for the .30/06 with Hybrid 100V and 220 gr Hornady bullets. The book maximum, from the Hodgdon web site, is 52 grs of powder, but I didn't run into high pressure signs until I hit 57 grs, increasing in one gr increments. Unfortuneately I experienced some problems with my chronograph yesteday, so I was unable to get a velocity reading, but I was attempting to get 2500 fps. I suspect a wire to one of the screens broke due to the cold temperature.
I have found all sorts of mistakes in a number of loading manuals, and all I can conclude from that is that the data came from a computer program, or the internal dimensions of their test barrels were far different from mine. One can only assume it is in the best interests of the people who publish those manuals that the best possible data is provided to the customer. When I come across a glaring mistake though, I cannot help but conclude that the data was obtained through a program rather than by actual firing. Perhaps Hodgdon entered the incorrect burning rate for H-100V which is closer to Re-19 than it is to H-4350, but again, all guns are individuals.
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Boomer please don't get me wrong, I am not disagreeing with you.
Many of the things we do, the loading procedures we go through, are correct and we end up with good, and safe, results. However, because of the complexities of what is actually going on after the trigger is pulled, results are often lumped together as either successful (gun didn't blow up) or unsuccessful (kaboom)
My discussions are here to demonstrate to readers that there is a lot more going on, and how some of the "factors" can be taken into account by other than trial and error.
As far as modelling in general and QuickLoad specifically, it HAS FULL CONTROL of EVERY parameter that you have mentioned. (case capacity as water volume, case design, bullet bearing surface, barrel friction, indirect throat configuration, etc...just to mention a few) It is a VERY sophisticated model and the majority of people will only scratch the surface of it's capability. It is usually used as a "load book" and not the comprehensive modelling tool that it is.
The interesting points I have been describing are:
Also note that I never gave exact numbers in my responses. I know very well that not everything is being taken into account so "exact" numbers would be meaningless.
Also, I am sure that the majority of people would not have predicted that with the above 357 loading, that peak pressure would occur after the bullet has travelled less than a quarter of an inch.
My responses are simply illustrating, in a simplified way, that there are a lot of factors that affect peak pressure and performance of a load, and that seemingly minor factors can substantially change the pressures generated.
If anyone is interested they should download the QuickLoad Demo. The best part is not the computer demo but the full Manuals that are included as PDF files. At the end of the Manual there is a comprehensive discussion of interior ballistics and what physical factors affect interior ballistics.
The discussions in the Appendix of the manual are general in nature and apply to all interior ballistics and how things like pressure and velocity are generated, powder burning characteristics, etc, (and they don't refer back to Quickload.)
http://www.neconos.com/details3.htm
Enjoy
Many of the things we do, the loading procedures we go through, are correct and we end up with good, and safe, results. However, because of the complexities of what is actually going on after the trigger is pulled, results are often lumped together as either successful (gun didn't blow up) or unsuccessful (kaboom)
My discussions are here to demonstrate to readers that there is a lot more going on, and how some of the "factors" can be taken into account by other than trial and error.
As far as modelling in general and QuickLoad specifically, it HAS FULL CONTROL of EVERY parameter that you have mentioned. (case capacity as water volume, case design, bullet bearing surface, barrel friction, indirect throat configuration, etc...just to mention a few) It is a VERY sophisticated model and the majority of people will only scratch the surface of it's capability. It is usually used as a "load book" and not the comprehensive modelling tool that it is.
The interesting points I have been describing are:
- Peak pressures are generated very soon after the cartridge is fired, typically before or as the bullet is leaving the case and as the bullet is engaging rifling.
- How seemingly small changes in things like case capacity and bullet seating depth can make huge changes to peak pressures.
- Bullet material/composition typically only makes a difference of several thousand PSI in PEAK pressure, and is due to the force required to engage rifling (or forcing cone) AND because this is also approximately the point in the burning curve where peak powder burning pressures are also generated.
- Beyond the initial engagement of the rifling, the bullet material/coating is where friction comes into play and affects velocity but not peak pressure. (it does affect the tail end of the pressure curve)
- Once engaged in the rifling, bullet composition makes (almost) no difference on peak pressure since pressures are well below the peak. In this part of the barrel (past the throat) pressures are well below peak, but the bullet material does make a difference in velocity. (through acceleration caused by the changing pressure behind it)
Also note that I never gave exact numbers in my responses. I know very well that not everything is being taken into account so "exact" numbers would be meaningless.
Also, I am sure that the majority of people would not have predicted that with the above 357 loading, that peak pressure would occur after the bullet has travelled less than a quarter of an inch.
My responses are simply illustrating, in a simplified way, that there are a lot of factors that affect peak pressure and performance of a load, and that seemingly minor factors can substantially change the pressures generated.
If anyone is interested they should download the QuickLoad Demo. The best part is not the computer demo but the full Manuals that are included as PDF files. At the end of the Manual there is a comprehensive discussion of interior ballistics and what physical factors affect interior ballistics.
The discussions in the Appendix of the manual are general in nature and apply to all interior ballistics and how things like pressure and velocity are generated, powder burning characteristics, etc, (and they don't refer back to Quickload.)
http://www.neconos.com/details3.htm
Enjoy
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- Location
- Somewhere on the Hudson Bay Coast
SandRoad, I will not dispute that the computer program is a useful tool for the experienced handloader who is also a technogeek. However, safe handloading practices, and safe procedures for working up loads have been developed since before the advent of smokeless powder. Using the chronograph to aid in load development is another useful tool, and for those who do not trust the procedure I have outlined can simply work up loads until the book velocity is attained, providing they have not ignored the pressure signs in doing so.
I don't care what the peak pressure number is of my loads provided: the rounds cycle without sticking, the velocity is within the acceptable range, accuracy is within the acceptable range, and provided the loads are safe in that neither my gun nor myself is damaged. Safe reloading practices have kept me out of harms way for 35 years of handloading thousands of rounds per year.
The question is what is the handloader with less experience to think if he discovers that his favorite .357 load, one that he thought was safe and having being worked up carefully, turns out to produce 10,000 pounds more pressure for a millisecond than the industry standard for that cartridge (and I'm not sure this would not be the case with any high performance heavy bullet load for that cartridge handloaded or commercial). What it could do is destroy his confidence in his loading procedure, and lead him to simply give up handloading or use loads that are far below the maximum safe level in his firearm. In the case of handguns in this country, this would make little difference other than to those of us who hold ATC's. However if there is a pressure spike upon ignition in a handgun cartridge, there is no reason to assume that a similar pressure spike would not occur with heavy for caliber rifle bullets or handloads that have the bullets seated long to contact the rifling. The key here is how do we interpret the information we collect. If the pressure spike you describe is of importance, it will show up on the brass, or on the functioning of the gun; and if it does we have exceeded the safe maximum load for our choice of components in our firearm.
What concerns me is that the interpretation of this information will cause some to consider many loads developed and used safely over a number of years, unsafe. As a result these programs will prevent us from exceeding or even meeting the criteria of factory ammunition and could at sometime in the future result in legal limitations being forced upon the handloading community.
I am curious though. Does QuickLoad consider the light loading of very slow powders in large capacity cases safe? Or is it able to recognize that the small powder charge can be driven into the shoulder of the cartridge by the force of the primer ignition, and form a plug at the base of the bullet which can result in pressures that exceeds the containment strength of the action?
I don't care what the peak pressure number is of my loads provided: the rounds cycle without sticking, the velocity is within the acceptable range, accuracy is within the acceptable range, and provided the loads are safe in that neither my gun nor myself is damaged. Safe reloading practices have kept me out of harms way for 35 years of handloading thousands of rounds per year.
The question is what is the handloader with less experience to think if he discovers that his favorite .357 load, one that he thought was safe and having being worked up carefully, turns out to produce 10,000 pounds more pressure for a millisecond than the industry standard for that cartridge (and I'm not sure this would not be the case with any high performance heavy bullet load for that cartridge handloaded or commercial). What it could do is destroy his confidence in his loading procedure, and lead him to simply give up handloading or use loads that are far below the maximum safe level in his firearm. In the case of handguns in this country, this would make little difference other than to those of us who hold ATC's. However if there is a pressure spike upon ignition in a handgun cartridge, there is no reason to assume that a similar pressure spike would not occur with heavy for caliber rifle bullets or handloads that have the bullets seated long to contact the rifling. The key here is how do we interpret the information we collect. If the pressure spike you describe is of importance, it will show up on the brass, or on the functioning of the gun; and if it does we have exceeded the safe maximum load for our choice of components in our firearm.
What concerns me is that the interpretation of this information will cause some to consider many loads developed and used safely over a number of years, unsafe. As a result these programs will prevent us from exceeding or even meeting the criteria of factory ammunition and could at sometime in the future result in legal limitations being forced upon the handloading community.
I am curious though. Does QuickLoad consider the light loading of very slow powders in large capacity cases safe? Or is it able to recognize that the small powder charge can be driven into the shoulder of the cartridge by the force of the primer ignition, and form a plug at the base of the bullet which can result in pressures that exceeds the containment strength of the action?
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You don't. You need pressure testing wquipment for that. Like the Oehler 83.
I hear you. But I neither own such equipment nor know anyone who has access to it.
So, my thinking is (magnum loads for an 158gr bullet):
lead bullet: 4.5gr to 5.0gr COL 1.61
Hornady XTP: 5gr to 6.1 COL 1.580 (shorter because it's a flat nose)
I have no-name bulk FMJ bullets and I can't seem to find any magnum casings. Therefore I want to use 38 spl brass, with the COL 1.610 and 4.5 to 4.7gr of titegroup.
On the other hand, I have read the thread from the guy who blew his GP100 with 7.2gr titegroup and that got me weary!
