.303 to .762x51

Sweet!

Keep us posted.

It has been a work in progress spanning 57 years🦊

I am hopeful as to how accurately it will shoot …

Please let us know how it shoots.  

I've seen a few rifles now with the No. 4 (T) cheek piece on the butt stock.  Not sure how well that will work with iron sights which are nominally only 1 inch above the bore.  On PH5C sighted rifles, I don't need any additional height on the stock for getting good sight alignment until reaching the 800 yard sight setting.  I have perhaps an unusual shooting position, my head is well forward on the stock and my cheekbone sits right on the base of my right thumb.  My eye is about an inch behind the aperture which allows me to close it down quite small to improve depth of focus and reduce sighting errors.   You might think recoil would push the rear sight into my eye, but nope.  I wonder if anyone else uses this type of hold/head position?

The L42 is of course the 7.62 sniper rifle converted from the No. 4 Mk I(T) which used the No. 32 scope, so the cheek piece is quite necessary.  I'm not sure how high above the bore the No. 32 scope is, I would guess at least 2 inches vs the nominal 1 inch above the bore with the PH5C (or original Mk 1 rear sight) with the standard blade front sight. 

The tunnel type front sight you have added might be higher above the bore than the standard blade.  I've got a A.J. Parker "matchmaker" tunnel type forsight fitted to my No. 4 DCRA 7.62 conversion, and it's a bit lower than the original blade foresight (mostly because the ring aperture insert uses a target center hold vs a blade which uses a 6 O'Clock hold on the target), I had to lower the rear sight by about 3 to 4 MOA with the tunnel front sight fitted. For me, it would be impossible to get eye alignment with the rear sight set at 200 yds with the cheek piece, YMMV.  

It’s not the height of the mount that matters, it’s the height of the mount plus scope rings and diameter of the scope tube.  The critical dimension is from bore centerline to scope tube centerline.  It’s really not possible that a scoped rifle to have the same height above bore as the original irons which are based on a nominal 1 inch height above the bore centerline. 

Here's a photo of my L39A1 alongside the No8 .22's and the No1MkIII*. Not a great photo unfortunately; but you can see that the heavy barrel is quite long compared to the SMLE. Also the fore end is shorter than the No8.

I regret not having the No4Mk1 in the same photo.

I would pont out that the gloss varnish is not standard and has since been removed and replaced with linseed oil! 

The Cheek riser is not standard on the L39; but this rifle came with it. I don't have an issue with it when using the dioptre rear sight.

I have a Schmitt Bender scope for this rifle, (which is currently on one of the No8's) but haven't got around to fitting it yet.

Much of this is your own preference and what you were taught. I do know I’ve seen other shooters and photos in training books on the LE’s showing fairly steep angles between the body and rifle (30 deg or so) with a well forward head position, cheek on right thumb, in the prone position.