Interesting rifle, a Hobart based Tasmanian Garrison issue. Lovely. The timber is English walnut, and will be exceptionally tough.
I'm going to describe my understanding and experience, and not pressure anyone to accept my view. I've restored about 25 rifles of vintages from 1900 to 1950, so I've made a few mistakes and learnt a little on the way. Your choice is entirely your own doing.
The "varnish" is almost certainly Birchwood Casey Tru-Oil. Comes off easily with Polystrippa (
Australian owner, local products). Off to Bunnings, if you wish. Won't harm timber, won't kill anything, provided you're careful and diligent in following manufacturer's instructions. Paintbrush application, and when bubbled, you can use a firm plastic putty/plaster spatula or scraper (Bunnings has several sizes) and use it with the blade at 90 degrees to timber grain. Once the bulk is off, you can then finish off with a well worked green ScotchBrite Scourer to remove all the coating and gelled gunk. Clean up with a lint free cloth wet with turps.
Once the timber is nice and dry and clean, you then do the
BLO/Turps 50/50 application. Again, and again until the timber won't absorb any more. Clean the residual oil off with a turps soaked lint free cloth. Allow to dry.
You now have a standard Service finish, you haven't sanded, haven't abraded, haven't damaged the timber. You have not detracted form the colour and grain of the timber.
You can leave it there.
Or....
You can go one step further and follow what the Yanks do with their Garands. And it's a great idea and very safe and protective. (Well done
Garand lovers!)
Melt pure beeswax (Bunnings, paint aisle) and mix 1/3 ratio of wax,
BLO and Turps. Allow to cool and solidify.
Wipe the wax on a small portion of the stock, work sequentially through connected areas, small parts at a time. Say, start on the flat right side of the butt. Wipe a liberal amount of wax compound on the timber, completely covering the area to be worked in one go. Follow the grain. Like planing, work with the grain. Work the wax in until it becomes difficult to rag in.
When done, here's where the sweat, muscle cramp and hard work comes in. Using the heel of your leading hand, work the wax in in long strokes following the grain. You'll feel that the effort increases as the wood "dries" or actually has the wax worked in to the pores. Keep going until you've got a hot and sore pal heel. The temperature of your skin will tell you how things are going. You're melting the wax and filling pores while this is happening, so no stops to cool down. Defeats the purpose.
Keep working throughout the entire furniture.
when you can't wax any more, because it won't absorb, that's it. The finish should be a sheen off matt but not gloss.
This is a natural protective coating that emulates decades of grease and grime that gets built up in Service. It does not damage the timber or the grain, it protects it with natural lubricants from oil, moisture and grit ingress. And looks brilliant.
So there you have it, an option.
Others may disagree and I completely accept their choice to do so.
But as a means of protective, preserving and highlighting the beauty of the timber, I reckon it's the Dick's Guts.
I've done a couple of late No 4's in Birch and Beech. The outcome is just brilliant. Not flashy, not glossy, but stops water ingress at the range and makes routine maintenance and cleaning a breeze. And it's replicating Service condition, only cleaner. (The waxy glossy look of old rifles is grime, oil and wax build up anyway)
Your call as to what to do. And as stated before, I'm not trying to force my view on anyone, only sharing what I've learned, done and like. Again, my thanks to the Garand enthusiasts that described the waxing technique.