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British System of Chamber Pressure Measurement

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Shamu View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: January 03 2021 at 3:14pm
Originally posted by Enfield Envoy Enfield Envoy wrote:

he!!o, many thanks... Quite a lot of answers Smile

This calculation let me think: 

The .303 Enfield is stamped 18.5 tons or 18.5 Tsi, which according to American test standards corresponds to a pressure of approximately 37,740 CUP or units of copper. Since the British used a different proofing method with oiled proofing cartridges and the base breaker method, the pressure values ​​differ from the American standards.

To convert the UK pressures values ​​to American test standards you need to add about 20%

.303 British 18.5 = 37,740 CUP + 20% = 45,288 CUP (18 or 18.5 ????)

The normal chamber pressure of 0.303 is 45,000 CUP or 49,000 PSI.

The 19 tsi for the Enfields No. 4 with 7.62 correspond to 19 x 2040 = 38,760 + 20% = 46,512 and "below" the evaluation of the converter method with 50,000 CUP or 60,000 PSI of the NATO cartridge with 7.62. (This could be why they require the rifles to be retested.) More information about the older testing methods and procedures is needed to know where we stand.

Later on, a mathematic error was detected and the CUP-Number according to this 19t-Proof seems to be:                19 x 2240 +20% = 51'072 CUP. How can i calculate the PSI ? Because, I don't think that an professional reloader can work really seriously without knowing this. A look at the loading data shows quite different gas pressure-numbers - within a given bullet weight/bullet-type - so how can we choose properly our load's ?.. Without experimenting for a long time.. ? 

Thanks.

A good evening to all of you.



Lets try this again, slowly.
There is no direct conversion between the 2 systems.
Its like trying to compare Centigrade to PSIG.
It simply won't give a valid answer.
First rule of reloading?
What is it?
"DO NOT EXTRAPOLATE OR INTERPRET LOAD DATA"

I STRONGLY urge you to follow safe reloading practices by making this paramount in ALL your reloading activities.

Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goosic Quote  Post ReplyReply Direct Link To This Post Posted: January 03 2021 at 3:24pm
Enfield Envoy. 
Reloading data is for you to follow directly with no other course corrections. 
Find a load suitable to your wants and start at the very beginning with data given.  If the load does not perform to your liking move up to the next grain/grams of powder in increments until you find the one that suites you and the rifle, never exceeding the maximum charge.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: January 03 2021 at 3:33pm
Exactly. If you don't have both a British (linear) copper crusher AND a U.S. Axial Copper crusher, as well as a pressure transducer on your test barrel and all the triage charts, for both systems, to read the results you can not know what pressures you are actually running.
Again
"DO NOT EXTRAPOLATE OR INTERPRET LOAD DATA"
Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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