PSI-C.U.P. conversions?
How do I convert a known pressure listed in P.S.I. into the C.U.P. unit of measure? Or the other way around.
Basically, I'm trying to decide if it would be safe to run .32H&R Magnum rounds through a model 1895 Nagant pistol (7.62x38R).
I have a Taurus .327 Fedmag that will run .327, .32S&W Long, and .32 S&W, as well as .32H&Rmag, so diameters are close enough. I've also read that I can shoot .32S&W Long through the Nagant, so I'm assuming the .32H&R mag round will be o.k. as far as diameter is concerned.
I can't find the 7.62x38R pressures listed in anything but C.U.P.
I'm finding the H&R Mag round is running about 21,000psi and the Nagant round is listed as 12,330 C.U.P.
Are these pressures anywhere NEAR close, or WAY out of the ballpark?
Thanks
Basically, I'm trying to decide if it would be safe to run .32H&R Magnum rounds through a model 1895 Nagant pistol (7.62x38R).
I have a Taurus .327 Fedmag that will run .327, .32S&W Long, and .32 S&W, as well as .32H&Rmag, so diameters are close enough. I've also read that I can shoot .32S&W Long through the Nagant, so I'm assuming the .32H&R mag round will be o.k. as far as diameter is concerned.
I can't find the 7.62x38R pressures listed in anything but C.U.P.
I'm finding the H&R Mag round is running about 21,000psi and the Nagant round is listed as 12,330 C.U.P.
Are these pressures anywhere NEAR close, or WAY out of the ballpark?
Thanks
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PSI to CUP CONVERSION FORMULA
CONVERSION FORMULAS
These formulas produce rough approximations and shouldn't be used as a precise or accurate result. There is no way to actually cross reference the two other than doing actual cartridge side to side pressure testing.
There is also the problem of not everyone understands pressure CUP OR PSI and getting the numbers mixed up in your mind is a real risk.
USE AT YOUR OWN RISK
PSI TO CUP
(PSI + 17902)/1.516
CUP TO PSI
-17902+(1.516XCUP)
(remember your math ditty...My Dear Aunt Sally Multiply, Divide THEN Add and Subrtact)0 -
The answer is Way Far Out.
In the lower ranges there is not a lot of difference in the numerical values for CUP and piezo psi.
The Nagant chamber is oversize for the 'Murrican cartridges and shooting them is a kluge to keep the old guns running on the cheap.0 -
CUP is a method using compression of precision copper cylinders of different dimensions depending on the pressure range being measured.
Deformation of a cylinder in the test fixture is compared to a tarage chart which gives pressure in copper units of pressure (PSI) vs length of compressed cylinder.
Piezo method uses a crystal that emits an electrical voltage proportional to the force exerted on it.It is assumed the later method more accurately determines pressure in firearms.
To my knowledge there isn't a simple corrolation.0 -
Every post is correct ... for as far as they go.
Years back I got tired of searching for a conversion for those two units of pressure that were aquired in different ways. I knew I had not seen one where anyone would take credit for it.
I went through every loading book I could to find pressure in CUP or PSI for the same load (in the calibers I use most). The values of CUP used were between 35,000 and 55,000...which suited my needs. I entered them into Excel and just plotted a linear best fit line. The R-Square was 0.92.
Yes, the physics of a copper crush is NOT going to be linear.
Different strain gages on different materials introduce some error.
It's not simple, as stated, but you can work within your loading range.
When I used 'my' equation and the 'Rio' equation they agree within 2.4 % for CUP of 35,000 to 55,000. (in that range ONLY)
Thanks Riomouse911 !0 -
No worries, I got that formula from a Marlin enthusiasts page. Like everything else off the net, take it with a grain of salt and make sure you're loading 10% under max to start. To see that the formula the guy put up was accurate to within about 2 and a half percent, that's not bad...especially when he did say it was a rough approximation.
I, too hate CUP / PSI comparisons, especially when they're in the same manuals for the same caliber. I wish they'd just stick to one or the other.0 -
To answer your question more constructively, I've read of the Nagant handling the H&R Magnum but in your shoes, I'd buy a replacement cylinder in 32ACP and rechamber it for the 32 H&R Mag.
32 brass in any size isn't the cheapest and it has value even if you don't reload so you don't want to screw it up in a bad chamber.
I don't know about the 327. You may get primer blowout at the least.
Of course you will lose the chamber sealing effect of the Nagant cartridge.0
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