MK 4

Hi - I have a Mk 4 on the end of the barrel it is stamped 18.5 tons per ?
What does that mean?

I believe the rear sights are original but my rifle came with another set - who makes this rear sight and is it better than the original? Any help would be appreciated

Thanks!

Export Marks Now this may well be one of the more common set of stamps. A set of information marks, that were stamped onto the rifle when sold out of service. That the rifle fired a ,303 projectile, the case max overall length was 2.222 in inch’s and it was pressure tested to 18.5 to ton. The BNP stood for British Nitro Proof, it was tested and passed Nitro proofing.

Agree with all above, the Mk 1 micrometer sight is much better and gives 1 MOA (one inch at 100 yards) elevation adjustments.  And if you are somewhat far sighted like I am, a reduced size aperture does wonders to help focus on the front sight.  Reducing the aperture size may not be allowed on some service rifle match rules. 

Thanks Shamu, this is more or less what I thought.  When you say the "original proof pressure was 18.5 tons per sq in" was this the actual proof pressures via copper crusher table?  I believe a oiled proof cartridge was used that gave considerably higher pressure than the standard service cartridge and the 18.5 (or 19.5) signifies the maximum average pressures that cartridges can be loaded to for public use.    

The .303 is usually proofed 18.5 tons PSI and the 7.62 NATO rifles were proofed 19.5 Tons PSI.

no doubt a NO 4 rifle , but im not happy with making all the leaps to a mkI* without some more photos or info , two sets of sights ? really - raises my "?" 

The spacer is just a little tube that slips on the pivot to fill the gap on the right hand side. #28 in the diagram, you can easily make one if you have the correct diameter tubing handy.