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Marking Identification

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britrifles View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: January 02 2022 at 5:00pm
Yes, that is all correct Shamu and consistent with what I’ve read about copper crusher methods.  The main point I wanted to make is that there is no direct relationship between the British “Base” method and the US “Radial” copper crusher method.  

The copper “crushers” were first prepared by pre-loading it with a hydraulic press under a pressure that was slightly below the pressure intended to be measured.  This was necessary to keep the displacement of the crusher in the test pressure gun to a relatively small amount and not cause a case rupture.  




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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goosic Quote  Post ReplyReply Direct Link To This Post Posted: January 02 2022 at 6:02pm
Originally posted by britrifles britrifles wrote:

The main point I wanted to make is that there is no direct relationship between the British “Base” method and the Radial” copper crusher method.  
The British "Base" method would then be the, "CORRECT" application to use foregoing all others in direct regards to the British made Enfield rifles?
I can only assume this of course...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: January 02 2022 at 7:06pm
Yes.
That's the source of much confusion!
The PSI in your SCUBA or whatever tank & that documented as "PSI" in a crusher are as similar as chalk & cheese.
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 02 2022 at 7:24pm
    I have always known this and have applied that knowledge to any Enfield I have or have had, including the one with the 7.62x51mm NATO chambered barrel. That being said. If there is ever a time when someone questions a particular load as to if it safe to use in a No4Mk1 and I happen to chime in with what I know to be true, rest assured, I have done the research and can attest to its validity...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: January 03 2022 at 3:09am
As to reloading, I’m of the opinion that it is perfectly safe to follow .303 British published load data by the powder manufactures, or other reputable sources such as bullet manufactures who have made pressure measurements. Those measurements are done using either the Radial copper crusher (CUP) or Piezo Pressure (PSI), and are safe providing they do not exceed CIP or SAAMI maximums.  

None of the reloading manuals have pressure measurements using the British “Base” copper crusher method that I’m aware of, so it’s not really possible to compare these loads to the .303 service ammunition.   I found only one published source (1960’s NRA reloading manual) that gave the pressure in CUP (radial method) of Canadian Mk 7 Cordite ammunition made in 1950 which gave 43,060 CUP for an average of 10 rounds.  That particular ammo was issued for the 1957 DCRA Canadian National Matches at Connaught ranges and is very accurate indeed, I still have a small amount of this ammo.  I wish I knew what that same load gave in the British “Base” pressure measurement system, but presumably somewhere around 18.5 tons per sq in. 

Where I get nervous is loading 7.62 Converted No. 4 rifles up to the maximum pressures for .308, as this is significantly more pressure than the .303, regardless of what measuring system is being used.  Will the action fail catastrophically from firing a few max pressure .308 loads? No, not if it had been proofed for 7.62 NATO and it is in good condition.  But, these higher loads on the bolt and action body will take its toll if this is continued for thousands of rounds.  So, I’ve typically kept my .308 loads to published minimums, or load to .303 velocities for similar bullets (i.e. load the 168 or 175 gr Sierra MatchKing in the .308 to the same velocity as the 174 gr Sierra MatchKing in the .303.   Charge weights for these loads are very similar. 

I’m afraid what has been lost to time is how the .303 British SAAMI and CIP standards were created in the first place, it is a military service round with design pressures established using the British System of Base Pressure measurement.  Military service ammunition pressure levels evolved over time, from the fairly low black powder round to the Mk 8 round which developed 20-21 tsi. Then there are the 7.62 conversions with even higher pressures. How did SAAMI decide the maximum pressure for the .303 is 45,000 CUP?  Perhaps they measured Mk 7 service ammunition in a test barrel with the radial copper crusher? 

Sorry if we have hijacked this thread.  This discussion would have been useful in the post I had started on the British System of Chamber Pressure Measurement. 


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