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jmharmon
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| Joined: | 13 May 2008 |
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Posted: 6 June 2008 08:56 PM |
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is there a calculation for finding out your psi of a cartridge?
I have both blackpowder and smokeless.
have an indian smle in 308 but want to keep the psi down to about
48-50 000 psi for safety sakes. 308 and 7.62 nato can go up to 55000psi and don't want to risk using a high pressure.
thanks for any help.
john
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smacks
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| Joined: | 4 August 2007 |
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Posted: 6 June 2008 11:36 PM |
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The only one I have found is in the Modern Reloading Second Edition Richard Lee Manual. I have two of the 2A1's and I have to watch it.
The Lee manual doesn't give psi on starting loads
The Hodgdon Annual Manual does Give psi in IMR powder but give cup in most all other powders.
Hodgdon gives 5 loads in IMR powders and all the "starting" loads are under 45,000 psi. I have only went about 2 grains above the starting load and had no problems.
The Lee Manual gave this calculation for figuring pressure for cast bullets, but the table shows working down from 51,000 psi and has to work through the cycle 14 times to get down to 29,000 psi.
This is for cast bullets but it will work for smokeless powder.
You just don't have to work it through as many times to get down to the neighborhood of 45,000 psi.
I checked it out with the pressure listed in the Hodgdon Annual Manual and it works out right.
If you have the Lee Manual it is on page 158.
The formula only works if you have a reference point to start.
Example, Lee manual doesn't give pressure for starting loads but does for most Never exceed loads.
You use the max psi and work down from there reducing "one" grain at the time till you get to the pressure you are looking for.
All most fool proof if you do it right.
Hope this helps. smacks
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Charley
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| Joined: | 9 September 2005 |
| Location: | San Antonio, Texas USA |
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Posted: 7 June 2008 03:37 AM |
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Some say you can somewhat calculate pressures, most say there is no way without proper equipment.
The Ishapore MK2 and 2As were designed for service with 7.62x51 Nato..308 runs at higher pressures than 7.62x51, and I sure wouldn't shoot it my rifle. I wouldn't have an issue with dropping most start data for the .308 by 10%, and working back up to the start load.
My 2A mostly sees use as a cast bullet launcher, so my loads are pretty mild anyway.
____________________
"You all can go to Hell, I'm going to Texas" David Crockett (and probably George Bush)
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smacks
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Posted: 7 June 2008 03:59 AM |
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The 48th edition Lyman manual gives pressure on starting loads.
I started out firing managed recoil factory ammo in mine.
When I started, I started with the starting load. I have only went one grain above the starting load.
I haven't had any trouble and got 5+ firings per case before having to full length resize.
"Do not" fire full factory loads in this rifle. He who says it is OK is full of it.
That formula I talked about also works.
Each time you work it it reduces the load by one grain, then you do it again with the new pressure , each time the pressure drops from 2000 to 3000 psi. till it gets where you want it. In the end count the times you worked it and subtract that from the max load. One grain for each time
Example, if the max load 50 grains and you went 5 times your new load would be 45 grains.
smacks
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smacks
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Posted: 7 June 2008 05:19 AM |
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By the way, I should have noted. This is not a calaulation.
It is a mathamatical formula.
If it is not correct then math is a lie.
smacks
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Charley
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| Joined: | 9 September 2005 |
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Posted: 7 June 2008 05:25 PM |
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Calulation, mathematical formula, ne le hace. GIGO, plain and simple.
Lyman and others that give a pressure figure also add a disclaimer that the pressure reading is for that particular lot of cartridges, loaded with those particular components, in that particular firearm or pressure gun.
You can come up with practical estimates of pressures, but you cannot say X cartridge loaded with X components will give X pressure in every firearm under every circumstance.
Starting with an unknown, and basing extrapolations on the unknown isn't likely to work. You can be in the ballpark, but it isn't going to be the same as measuring the pressure with proper equipment.
Is it safe to guesstimate pressures, using the factors we can measure or see out of a lab? Sure, we do it all the time. Is it the same as an absolute measurment? Not hardly.
Last edited on 7 June 2008 05:28 PM by Charley
____________________
"You all can go to Hell, I'm going to Texas" David Crockett (and probably George Bush)
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runfiverun
HB Full Member
| Joined: | 9 February 2008 |
| Location: | Soda Springs, Idaho USA |
| Posts: | 70 |
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Posted: 8 June 2008 06:00 AM |
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and yet the factory stuff that is tested on all that equipment..
it is still gonna be diffrent in your rifle.
so doing the math and lowering the load is still about as close as what the
factory lab tested stuff is.
could use a quickload program, it will give you an idea also.......
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smacks
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Posted: 8 June 2008 06:48 AM |
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looks that way
smacks
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