Nr. 4 Mk 1 Barrel Markings - Need help

[LA Gman]

I recently inherited a Nr. 4 Mk 1 after my Father-In-Laws passing and have been researching as much as I can about it. Unfortunately I do not know the story of how he came to posses it.
I am pretty sure by the markings that it is a 1944 ROF Fazakerley rifle and the markings on the stock under body forward match the rear band (MB21601).
What I can't find are any reference to "Barrel Markings. I have attached a photo of the barrel tip and those markings stamped into it.

Any information would be greatly appreciated.
Thank you,

Information

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[Alan de Enfield]

I recently inherited a Nr. 4 Mk 1 after my Father-In-Laws passing and have been researching as much as I can about it. Unfortunately I do not know the story of how he came to posses it.
I am pretty sure by the markings that it is a 1944 ROF Fazakerley rifle and the markings on the stock under body forward match the rear band (MB21601).
What I can't find are any reference to "Barrel Markings. I have attached a photo of the barrel tip and those markings stamped into it.

Any information would be greatly appreciated.
Thank you,

The muzzle markings are UK Civilian Proof markings, the tests were undertaken by the London Proof House

Calibre = 303
Cartridge length 2.22"
Test pressure = 18.5 tons per square inch

Side wall markings

No4 Mk1
ROF(F) = Royal ordnance factory Fazakerley
Date of manufacture = April 1944

Butt Socket marking
Serial number = MB21601

[LA Gman]

Thank you so much. I really appreciate it!
I can't wait to fire it. I had it cleaned and inspected already.

The muzzle markings are UK Civilian Proof markings, the tests were undertaken by the London Proof House

Calibre = 303
Cartridge length 2.22"
Test pressure = 18.5 tons per square inch

Side wall markings

No4 Mk1
ROF(F) = Royal ordnance factory Fazakerley
Date of manufacture = April 1944

Butt Socket marking
Serial number = MB21601