Anyone know of a source? These are smaller than the current production 110 etc. Numrich is out.

Why use one? Put a normal shoulder on the barrel. If you can't do that, just machine one out; internal threads.
I wouldn't use one if I had it; all those grooves look wrong.

Out of the box thinking! Way to go. Already bought the tap for the internal thread, fortunately it's standard 7/8-18. I hate cutting internal threads.

This is how I keep getting into the parts business ... make one, may as well make 10. Think I will cut the OD so one can use a regular Craftsman ring wrench, since nobody seems to have the special wrench either. Last time I did this (Win 1894 takedown action extension) I made 5 from the same bar and have 2 left. Also got into this with Martini parts (Greener three lobe cocking lever/tumbler, cadet extractor, large frame Greener extractor ...). On the list are centerfire breech blocks for the Stevens 44. As best I could tell, all of these parts are NLA.

Make a wreech? I did, two of them, large and small

You do not need a wrench; make them smooth. You ain't tightening the lug nuts on a Kenworth.
Cutting internal threads is just like external ones. Only the opposite.

I use a lot of these:

I like to be able to see my threads while I am cutting .. and boring bars bend which makes things a little tricky if you are going deep, which I plan to do as I will use a 12" tube as the starting point to yield 10 of these parts. With internal threading, you have to remember to back out backwards, unless you can go all the way through. I have done it, even square threads, but I don't like it. I once made a bunch of quarter ribs this way .. cutting a negative of the barrel profile inside a tube manually is interesting to say the least.

Wisner reminded me that later, savage went to a smooth nut with a blind hole for a spanner. I guess you can face off the nut to get the hole under the stock line. So maybe that's the most elegant solution.

Using those orange wrenches is what got me into the predicament in the first place. Nut would not yield to penterating oil, heat, clamping in barrel vise nada. There is not good way to grip the action, it's round. Eventually put action in barrel vise, wrapped nut in Al sheet and applied the pipe wrench. No luck. Pipe wrench and sledge hammer. No luck, just perforated the Al and chewed up the nut. So I milled it off after wasting a lot of hours trying to save it.

Not sure why you are making more than one nut; I can't see any possible demand.
Anyway, I have removed a lot of Savage nuts (none from a 340) and they were not very tight.
I use an internal action wrench for round actions and clamp the nuts. For a 340 make an L shaped one that goes into the square locking lug slot. Or for one, I would make the nut a bit oversize, use the pipe wrench, and machine off the wrench marks. Lots of ways to do it.
When I do a Savage I rarely put a nut back on it; easier and looks better to just put a barrel with a shoulder on it.
Some current Savages have smooth nuts. Some have one notch. Not hard to remove; I guess back when they made the 340 they horsed them on.
The most elegant solution is to make them octagon.

I think someone hot-blued this barreled action at some point which froze the nut.

The action does not have a lug raceway, it has a split bridge for the single bolt lug. The lug cutout is 360 deg, nothing for a wrench to grab.

The reason I need said nut is the barrel I am using is only 1.0" at the breech. Not enough to cut a shoulder. The factory barrel is 7/8" at the breech end, so I will turn it down to match the same contour, thread it long, and make a nut.

It's actually a rather nice, beefy little action. Extractor is a bit light duty, needs a side mount if you are going to scope it (or a custom top mount) but otherwise it looks great. The stock was crappy on these guns but Richards will solve that. Will make a nice brush gun when I am done. I am partial to ghost ring setups so no side mount.

The reason Numrich is out of nuts is they sold them all .... and apparently they bought up the entire inventory of 340 parts when production ceased. And the setups for one nut is much the same as the setup for 10 nuts ... if not someone, some day, will buy a box with 9 Savage 340 barrel nuts in it and wonder what and why.

I would thread the barrel, and slide on an unthreaded spacer, jammed against the barrel shoulder. Threads are not necessary. You have plenty of shoulder to stop it. The British did that; called Breeching Washers. Just trying to avoid work.
That receiver does have a slot in it for the bolt locking lug, at the top.

Yes you are right there is a slot at 12 o clock but it's a tiny slot not very long and not deep either ... mess that up and the action is toast. I think the barrel nut design was adopted precisely because there is no way to get a good wrench grip on this action. Easier to clamp action in blocks and tighten barrel nut .... but I do appreciate the suggestions, learn something every day.

there is already a washer on this action .. recoil lug ..

I don't mean a thin washer; I mean a piece like a threaded collar, but without the threads; the only reason for a threaded nut is so they can do two things; use small diameter barrel blanks, and set headspace without any machine work.
Neither of which you need to do. Your barrel blank will have a little shoulder. The spacer, we'll call it, is only there to fill up the gap in the stock. No real need for it to be threaded because you have a 1/16th shoulder.
I'm always just trying to get out of work!

Both Tom and Russ need to work more on these delightfull rifles.

The simplest action wrench is a bar of steel that is machined to be tightly fitted to insert from the bottom of the magazine well, and up into the top lug recess.
Will need three sizes, one for the 30-30, one for the 222/223 and another smaller one for the 22 Hornet

The proper way is to make up a split action wrench that will clamp around the front of the receiver, and has a milled slot to accept the matching insert that will slide up into the magazine well, and is held in place with a screw.
That way it is clamped around the receiver ring, and the insert is up into the magazine well opening and is also clamped in place. Nothing will move then

Years ago Dad made up a slotted nut wrench, took a flat scrap piece of steel about 3/4 thick x 2 inch wide and over a foot long, made a round cut in it slightly bigger than the nut
This round cut went part way into the side of the steel bar. Then took another smaller flat piece of bar stock and ground one end on it to match the round slots in the barrel nut.
Got the bar/wrench and the one piece all lined up on a barrel nut and welded one end on the bar and piece of steel all out side the end of the barrel nut with out touching the barrel nut
Then remove the soon to be spanner wrench, and weld the end on the one piece onto the finished barrel wrench, with some minor deburring at the weld.

So now you have a spanner wrench with one flat piece of steel welded onto the end of the wrench to line up with the slots in the barrel nut.
That was 30 odd years ago and it still works today

The later barrel nuts with the single hole in them, the spanner wrench is even easier to make, you simply have to drill a hole the correct size in the radius cut in the wrench and insert a pin.

Dad has one gun that has been rebarreled to 25-35 and is tempted to make another in 7x30 Waters.

Jim Wisner

Yes but your father was a gunsmithing genius.