UK 1954 Rules of Proof

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   For those hopelessly technically inclined and always thirsty for knowledge, you might find this article interesting.  It describes the introduction of the 1954 Rules of Proof in the UK for sporting and target arms.  
This Rule is what resulted in the typical markings we see on Lee Enfield rifles released from service after 1954 which  show the following markings along with the new BNP (Birmingham Nitro Proof) marking:

.303"        
2.222"
18.5 Tons per [] "

The [] symbol above is intended to be a square shape, indicating a pressure value in British Long Tons per square inch.  

The new 1954 London Proof House marking is also shown in the article. 

.303" is the bore of course, and 2.222" is the cartridge case length.

This article definitively says that the pressure markings show the highest mean service pressure of the ammunition intended for the firearm, it is NOT the proof pressure (which was to be 30 to 45% above the mean service pressure for rifles).  

https://randywakeman.com/RulesOfProof1954.pdf

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britrifles Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: February 03 2018 Location: Georgia, USA Status: Offline Points: 8404	Post Options Post Reply Quote britrifles Report Post Thanks(1) Quote Reply Topic: UK 1954 Rules of Proof Posted: August 27 2024 at 10:53am
	For those hopelessly technically inclined and always thirsty for knowledge, you might find this article interesting. It describes the introduction of the 1954 Rules of Proof in the UK for sporting and target arms. This Rule is what resulted in the typical markings we see on Lee Enfield rifles released from service after 1954 which show the following markings along with the new BNP (Birmingham Nitro Proof) marking: .303" 2.222" 18.5 Tons per [] " The [] symbol above is intended to be a square shape, indicating a pressure value in British Long Tons per square inch. The new 1954 London Proof House marking is also shown in the article. .303" is the bore of course, and 2.222" is the cartridge case length. This article definitively says that the pressure markings show the highest mean service pressure of the ammunition intended for the firearm, it is NOT the proof pressure (which was to be 30 to 45% above the mean service pressure for rifles). https://randywakeman.com/RulesOfProof1954.pdf

Shamu Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Logo Designer / Donating Member Joined: April 25 2007 Location: MD, USA. Status: Offline Points: 20510	Post Options Post Reply Quote Shamu Report Post Thanks(0) Quote Reply Posted: August 27 2024 at 11:34am
	Yes I'd heard the figures of 5/3 Rds over pressure for proof loads.
	Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)

Sapper740 Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: July 15 2021 Location: Texas Status: Offline Points: 1737	Post Options Post Reply Quote Sapper740 Report Post Thanks(0) Quote Reply Posted: August 27 2024 at 12:01pm
	Much good info in The Standard Directory of Proof Marks by Gerhard Wirnsberger. Heavily slanted to German stamps but comprehensively covers British proof marks and stamps too.

britrifles Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: February 03 2018 Location: Georgia, USA Status: Offline Points: 8404	Post Options Post Reply Quote britrifles Report Post Thanks(0) Quote Reply Posted: September 09 2024 at 9:12am
	Just noticed a small subtlety in the article I posted here about the 1954 proof markings. For "sporting and target arms", the London Proof markings were different than the Birmingham Proof markings. London NP 18.5 Tons Birmingham BNP 18.5 Tons per [] " I've seen some Lee Enfield rifles with the London proof marks on this forum. 1954 is the first time that the rifle was marked with the maximum service pressures for cartridge's intended for the firearm.