I believe your rifle is a No4MkI*. The sight with screw adjustment are much better than the sprung slide of the type currently fitted. I have recently swapped the same for my latest No4 rifle. The "Singer" type sight with it's screw adjustment allows adjustments of about 1MOA per click.

The slide type has less accurate adjustment and is not easy for target shooting; as I found out recently. Seemed to be around 3 or 4 MOA between each point of adjustment.

I've never quite figured out the math on the pressure rating of 18.5 tons per sq in.  The British Ton is 2240 lbs, so that's 41,440 psi.  I thought the Mk VII ammunition was rated at 19.5 tons per sq in (46,680 psi).  SAAMI specs show 49,000 psi for the .303 British.  Is this because of the different methods of measuring pressures (piezo vs copper crusher, etc.)?  What am I doing wrong here? 

 

 

The British proof was done before the rifles were sold to the public.

Best,

R.

Bit more info & a minor correction.

From the picture of the stamped sight it seems to be missing a spacer (little cylinder) on the right hand end of the pivot.

If you flip it up does it slide from side to side?

If so definitely replace it with the micrometer screw version.

The spacer was made to allow for the reduced width of the stamped sights & without it they can flop all over the place, but its not needed for the cast singer type.

Tap out the cross pin on the left hand end of the "screw" shaft that acts as a pivot. It ONLY comes out from the bottom up the pin is tapered.

Push (don't try to unscrew the shaft is not threaded) the cross axis out to the right while pushing down a little on the sight body to release spring tension.

When the shaft is removed the plunger & spring will pop the sight up.

Remove it & drop the new one in to the same spot.

Push down & slide the axis pin (its correct name) back in fully.

NOW we use the slotted head to rotate the shaft till its hole lines up with the cuts in the frame & tap the little pin back in from the top.

Sounds tricky but takes about 5 minutes.

Re-zero for the new sight.

The

is the British Civilian proof marking from the Birmingham Proof house, its needed by law when selling a firearm to a civilian market in the UK.

The "export mark" referred to is the other part of the stamp, which maybe somewhere else. Depending on when it was Imported into the US (pre or post 1968) it will be either "ENGLAND", or later the importer's address.

Something like:

being a popular one.

Its a combination of 2 things.

The original proof pressure was 18.5 tons sq", but they were later reproofed to the higher 19.5.

It was all copper crusher & the "P.S.I." isn't actually "Pounds Per Square Inch" in the same system as things like air tank fills but a different setup entirely. Its actually read from a table depending on the reduction of length of the copper pill from the crusher.

Just to make it utterly confusing there were 2 methods of copper crusher test, one with the case drilled with a hole so the gas pressure acted by direct impingement on the pill's inner face & the other without so the case expansion created the crush effect.

Hey it worked! The "Dammed Fuzzy-Wuzzies" never figured it out!

The previous post should have read...

Shamu mentioned about a spacer for this sight to keep it from moving back and fourth - I don't have this spacer (maybe someone can attach a picture of what one looks like).

I will definitely replace the old sight with the micrometer sight.

Once again thanks for all the input on the sight and the stamping on the barrel - makes sense now! 

all the rest of the info regarding the sights is great , and correct as well , but i would love to know more of this rifle , it is NOT A MKIV OR A MK4 

I appreciate the diagram of the sights - thanks.