Max pressure in CUP or PSI
- Thread starter maxinumarmor
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The conversion factor from CUP to PSI is roughly about 1.15, therefore 60,000 CUP would be an overload in most bolt gun cartridges and relates to about 69,000 psi. According the various loading manuals, either of those cartridges can be loaded to a maximum of 55,000 CUP or 63,250 PSI, but IMHO that is too much for either of the rifles you mention, which is what I believe to be the information you're after. Beyond that the pressure figures don't have much relevance to a handloader unless he has a strain gauge to work with.
CUP and PSI don't directly convert or translate. Modern manuals use PSI, the older ones use CUP. If you can, read the article "Why ballisticians get grey hair" in Speer #14, it gives a pretty good overview on the headaches switching over caused. Also explains why a number of proven loads, were suddenly considered unsafe. PSI can be measured down to the 10th of a millisecond at a time, and if you had a spike that lasted exactly that long, that went over the top PSI value, then the load would be considered to be unsafe. Whereas with the old copper crusher method, it only told you the highest sustained pressure, tiny spikes, wouldn't have enough time, to show up using that method. Obviously, company lawyers would be upset with the company posting data, that testing says to be unsafe, even for insignificant periods of time, due to liability issues. This is one of the reasons for why guys will say the modern books have been lawyerized.
Thanks guys i was just wondering what the factory set as a max for these rifles i am going to try and keep it to 34 000 to 42 000 cup while trying to get some good FPS numbers.Was looking at that hodgdon reloading data site and noted there maxs were quit high and don't want to go anywhere near my maxs set by the factory for my rifles.The only info i found was the NO4 MK1* in 7.62 is about 19T to 20T per square inch and the SAFN49 8mm is about the same.[which is a auto loader] so whatever that works out to in CUP pressure.
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- Somewhere on the Hudson Bay Coast
Its fine to convert provided that you understand that the conversion is an approximation and not a hard value, and is used to put things into perspective rather than as a calculation for tweaking loads. But then again, without access to some sophisticated equipment, neither PSI or CUP should be a guide for tweaking loads. What you can determine is that an action which was rated for 50,000 psi would be unsafe with a load that produced 50,000 cup.
So if i keep my pressures in the 30 000 to 40 000 CUP range i should be pretty safe?
What my point is here is trying to get the most possible FPS while keeping the lowest possible pressures i may have to give up a little FPS which i most likely won't notess but it will be easier on the rifle and my casings will last longer.
Here is a link that people may find interesting i found related to temp. and how well your rifle/load does in hot or cold temp. outside.
http://www.hodgdon.com/smokeless/extreme/page2.php#top
What my point is here is trying to get the most possible FPS while keeping the lowest possible pressures i may have to give up a little FPS which i most likely won't notess but it will be easier on the rifle and my casings will last longer.
Here is a link that people may find interesting i found related to temp. and how well your rifle/load does in hot or cold temp. outside.
http://www.hodgdon.com/smokeless/extreme/page2.php#top
Other than an "interesting" detail to read about, I completely ignore CUP & PSI numbers. Since I have no way of measuring them, they are pretty much useless to me. I watch the shells, primers, and signs from the gun as I work towards the limits to tell when I'm at the Max for that specific gun.
That said, Yes, I think 30K to 40K CUP should be fine. Most guns like you described seem to be at or over the 45K range.
That said, Yes, I think 30K to 40K CUP should be fine. Most guns like you described seem to be at or over the 45K range.
Yes i notessed that there is 2 powders i am checking out info on that are 37 400-37 600,i think that is about as low as it goes with good FPS still.
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Better yet, don't use CUP at all. It is an extremely hokey measurement system, rather akin to using a system of "feet" for measurement, wherein every individual takes off his shoes and uses the length of his own foot as a measuring tool.
The only time i look at it is when i am shopping for powder i try and find the powder tests with the most FPS and the lowest pressure that is suited to the rifle it will be used in,then i take into account barrel length with the primer used along with outside temp.,without your own test equipment that is about as close as your going to get it.
EX. :My SAFN49 8mm auto CCI 250 primer 23.5 inch barrel will see only range time on a good day.
My NO4 MK1* 7.62 30 inch barrel bolt action CCI 250 primer hunt and target with it could see any type of outside condition including winter temp.
other rifles used for the same thing [NO4s] 303 25.25 barrel,308 win 22 inch barrel lever,99c and 99f 22 inch barrel lever
EX. :My SAFN49 8mm auto CCI 250 primer 23.5 inch barrel will see only range time on a good day.
My NO4 MK1* 7.62 30 inch barrel bolt action CCI 250 primer hunt and target with it could see any type of outside condition including winter temp.
other rifles used for the same thing [NO4s] 303 25.25 barrel,308 win 22 inch barrel lever,99c and 99f 22 inch barrel lever
Maxin - The safe and easy way to keep pressures moderate involves a loading manual and a Chrony.
Use a powder listed in the manual as suitable for your caliber (4896, RL15, 748, for example), start with a START laod and use the Chrony. If you want moderate pressure, add powder until you get a medium velocity, according to the manual. With a suitable powder, there is a direct link of pressure to velocity.
CUP and PSI are different measuring systems. In the case of 308 (and some others) the place on the case where the pressure is taken is differrent. This changes pressure readings a bit, so for this reason CUP cannot be converted to PSI for all calibers. In some calibers, the pressure limits are identical. In others, the numbers are quite different.
Use a powder listed in the manual as suitable for your caliber (4896, RL15, 748, for example), start with a START laod and use the Chrony. If you want moderate pressure, add powder until you get a medium velocity, according to the manual. With a suitable powder, there is a direct link of pressure to velocity.
CUP and PSI are different measuring systems. In the case of 308 (and some others) the place on the case where the pressure is taken is differrent. This changes pressure readings a bit, so for this reason CUP cannot be converted to PSI for all calibers. In some calibers, the pressure limits are identical. In others, the numbers are quite different.
Thanks i was in the begining just wondering if anyone knew the maxs for my rifles pressure wize.
I have a manual but no chrony like i was saying above i pick a powder from the manual or the linked site on this forum with the lowest pressures with good FPS keeping it between 30k and 40k CUP alot of the powders are in the 40k range not much choices but a good start.Also depending on which powder i choose i have to take outside temp.into account.
I have a manual but no chrony like i was saying above i pick a powder from the manual or the linked site on this forum with the lowest pressures with good FPS keeping it between 30k and 40k CUP alot of the powders are in the 40k range not much choices but a good start.Also depending on which powder i choose i have to take outside temp.into account.
The 8mm x 57 is an odd-ball, pressure wise. It was originally loaded at higher pressure than 7x57. Similar specs to 30-06.
However, SAAMI (American standards) were concerend about some liability issues. There were rifles extant that were unsuitable to full power ammo because the barrels were the "old" 8mm with .318 groove diameter. The new bore diameter (and bulet diameter) is .321"
If I had a semi-auto, I would start loading it at the "start" load and work up to find the laod that functioned the rifle and grouped well.
Read you loading manual. What I have written is probably there.
However, SAAMI (American standards) were concerend about some liability issues. There were rifles extant that were unsuitable to full power ammo because the barrels were the "old" 8mm with .318 groove diameter. The new bore diameter (and bulet diameter) is .321"
If I had a semi-auto, I would start loading it at the "start" load and work up to find the laod that functioned the rifle and grouped well.
Read you loading manual. What I have written is probably there.
