how do you know what max pressure of a barrel is?
- Thread starter AKD
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Wilfred - All the reloading manuals describe the pressure signs... However, as posted above, some rifles will exhibit no overpressure signs for hot loads. So a load the you have used successfully in one rifle, may be a bomb in another rifle. Using a chrony is certainly beneficial, as stated above.
I've reloaded for about ten years, and I dont have regular access to a chrony. I tend to stick at the minimum load end of the scale. I cant recall ever getting closer than 2 grains to published max. The reasons I do this are simple:
- Its a buffer against the inevitable reloading mistakes.
- Why take the risk? (Perhaps spending 6 years in mech engg studying the "perversity of inanimate objects" has caused me to feel this way.)
If you've detected a condecending tone in some of the posts above, there's good reason. Perhaps the most common reloading newbie mistake is assuming that published max load is the achievable max for their rifle. Its not, and most neophites wouldnt know how to ascertain what is.
Barrel rifles are extremely highly stressed - perhaps the greatest in the engineering applications I'm aware of. They are required to be made of steels that are much stronger than average - usually through alloying and heat treatment. The factor of safety at "rated" pressure (SAMMI, etc) is also very low by most engineering standards.
The majority of rifle failures are with reloads - manufacturers will void warranty if reloads are used. Factory loads, in many calibers, are well below rated pressure. The fact that a lot more reloading failures dont occur is testimony to the manufacturers of rifles.
I've reloaded for about ten years, and I dont have regular access to a chrony. I tend to stick at the minimum load end of the scale. I cant recall ever getting closer than 2 grains to published max. The reasons I do this are simple:
- Its a buffer against the inevitable reloading mistakes.
- Why take the risk? (Perhaps spending 6 years in mech engg studying the "perversity of inanimate objects" has caused me to feel this way.)
If you've detected a condecending tone in some of the posts above, there's good reason. Perhaps the most common reloading newbie mistake is assuming that published max load is the achievable max for their rifle. Its not, and most neophites wouldnt know how to ascertain what is.
Barrel rifles are extremely highly stressed - perhaps the greatest in the engineering applications I'm aware of. They are required to be made of steels that are much stronger than average - usually through alloying and heat treatment. The factor of safety at "rated" pressure (SAMMI, etc) is also very low by most engineering standards.
The majority of rifle failures are with reloads - manufacturers will void warranty if reloads are used. Factory loads, in many calibers, are well below rated pressure. The fact that a lot more reloading failures dont occur is testimony to the manufacturers of rifles.
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Want a decent bit of a read? Dig out a copy of Hatcher's Notebook. Lot's of info from an era where firearms development and metallurgy were really starting to be understood, and a fair bit of failure analysis.
Find a copy of Howe's Modern Gunsmithing. Another good book.
If you want specific answers to 'exacts', you should head to the nearest college or university that does some engineering, and start into the library. The ASM (American Society for Metals) publish a series of books that cover strengths of materials, machining, etc. Too damn expensive to buy outright, but used copies can sometimes be found.
Take a look at some of the stress analysis on Varmint Al's website. Good stuff. Dry as a popcorn fart, but good stuff.
You can spend the rest of your life researching this crap. If you are not doing engineering studies, and tying this in that way, read the forward in the reloading manuals, look at the pictures, and learn to recognize the signs of an overpressure, as well as understanding what the limits may be that separate one firearm from another, as far as the pressures that they will handle, given that they may be chambered in the same caliber. A good example of that would be the load data given in any manual I have seen, for the 45-70. Usually they offer up three different sets of loads, for three different strengths of action. They explain it in the book.
Not saying you shouldn't be interested, just that you should have an honest look at what variables you can change, and what you cannot. Unless you are in a position to make, or have made, barrels from scratch, getting all learned up on the strength of them is not of much practical use. They are rarely the weak link in the equation.
Cheers
Trev
Find a copy of Howe's Modern Gunsmithing. Another good book.
If you want specific answers to 'exacts', you should head to the nearest college or university that does some engineering, and start into the library. The ASM (American Society for Metals) publish a series of books that cover strengths of materials, machining, etc. Too damn expensive to buy outright, but used copies can sometimes be found.
Take a look at some of the stress analysis on Varmint Al's website. Good stuff. Dry as a popcorn fart, but good stuff.
You can spend the rest of your life researching this crap. If you are not doing engineering studies, and tying this in that way, read the forward in the reloading manuals, look at the pictures, and learn to recognize the signs of an overpressure, as well as understanding what the limits may be that separate one firearm from another, as far as the pressures that they will handle, given that they may be chambered in the same caliber. A good example of that would be the load data given in any manual I have seen, for the 45-70. Usually they offer up three different sets of loads, for three different strengths of action. They explain it in the book.
Not saying you shouldn't be interested, just that you should have an honest look at what variables you can change, and what you cannot. Unless you are in a position to make, or have made, barrels from scratch, getting all learned up on the strength of them is not of much practical use. They are rarely the weak link in the equation.
Cheers
Trev
Primer pockets are one of the most reliable methods of determining if a load is safe in your gun.Once you have worked up a load while seeing no other pressure signs,load up five new cases with that load.Fire and reload those same five cases five times each.If the primers still fit snugly into the primer pocket after five firings the load is probably safe in your gun.If the primers go into the primer pocket much easier after five loadings,the load is too hot for your gun.
Thanks for reminding me about Varmin Al's. I have a look at it before I had any background, and its a whole lot better now. I don't find it dry at all, with the animated models and all, it's one of the best sites out there. Can't believe I forgot about it.
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Yes........and here is the remaining bit of clarification:
The internal gas pressure loading on a pressure vessel (the radial loading vector) is manifested as three principal stress vectors within the vessel material; the tangental stress, shear stress, and longitudinal stress vector components. These stresses within the vessel material vary in magnitude as a function of wall thickness and radial displacement from the internal surface according to Lame's equation for thick wall cylinders (the inside chamber surface experiences the highest stress, and the stress on the material is least at the external surface of the chamber). So, yes, the tangental and shear stress components the barrel material experiences at the internal surface are greater than the radial gas pressure loading vector..........I shall take my lumps for the over simplification in my first post of this thread.
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Primer pockets
All the signs of excess pressure have to be taken together,primer pockets,primer radius,case head expansion,bolt lift, case head burnishing markings,report, and of course velocity.
Primer pockets life varies with the make. I have some butter soft Norma that doesn't last the 5 firings.I have pretty good idea of the pressure of the 30-06 load,N-560 and 180gr Interbond,as I've seen pressure gun results.It not even 30-06 book max.On the other hand I have some Winchesters,they last forever.
All the signs of excess pressure have to be taken together,primer pockets,primer radius,case head expansion,bolt lift, case head burnishing markings,report, and of course velocity.
Primer pockets life varies with the make. I have some butter soft Norma that doesn't last the 5 firings.I have pretty good idea of the pressure of the 30-06 load,N-560 and 180gr Interbond,as I've seen pressure gun results.It not even 30-06 book max.On the other hand I have some Winchesters,they last forever.
Yep, thanks for filling in the rest. In my post I didn't really want to get into the details, just enough to try and prevent confusion. As with many complex things, we try to over simplify as an example, and then sometimes it is taken as gospel.
And I also like Varmint Al's site.
Primer pocket life does vary with brass hardness,but if the primer pockets are loose after five firings,the load is too hot for your brass,in your rifle.
As for pressure gun results,if the pressure measuring devices were not installed on your gun,the pressure readings don't mean much.Due to differences in chamber and barrel dimensions,the chamber pressures can vary significantly from gun to gun using the exact same load,and the same exact components.
