thanks, jim

"858" major with 18 V threads per inch and shank 1.900" long for 340 types. NRA Gunsmithing Guide, 1982.Jul 6, 2019"

From Google search

You should measure what you have (the takeoff). The thread is .875 (7/8")-18 nominal. To flatten the crests a bit you will end up around .870". 858 is on the small side.

To make sure everything is of equal dimension, I run a 7/8-18 tap through the action and the barrel nut so you know what you are dealing with. Sometimes the tap is tight, sometimes it's not. I suspect it has to do with the wear on the factory tooling.

Note, there are no more barrel nuts available, and it's sometimes hard to remove one without damaging it (if rifle has rust or has been reblued, it's impossible to remove the barrel nut at all. So you can make a barrel nut (for which said tap will come in handy), or you can put a conventional shoulder on the barrel.

Looking at my Stevens/Savage rifles, I see 4 variations of the lock nut.

The early 325 had a concave radius in the front section, and deeper slots, then they went to a slight convex radius on the front section with the deeper slots.
I also have 2 rifles with much shallower slots.
Then the last rifles Savage made had only one round shallow hole for a spanner wrench, no slots.

The OD of the nuts run from 1.156" to 1.175" depending on vintage of the rifle.

So much for making a one wrench fits all the nuts

J Wisner

I just measured a takeoff, dia is .865 on this one, but it may be a replacement barrel as it has no logo or caliber marking on it ... but then again they started putting the logo on the action at some point. I had to cut the nut off, it was seized pretty well.

This whole affair is the quirkiest design I have seen. Barrel nut, coned breech, split rear ring, non-removable trigger assy, no good place for an action wrench to grab the action, butternknife bolt on the earlier ones, only one action screw and so on. The ejector on the early guns is something to behold and makes stock inletting a huge pain.

ive thought about rechambering a 30-30 barrel to .30 carbine if the barrel tenon is long enough to cut threads on, after the barrel is set back enough to clean up the chamber... and yes i know the twist for the .30 carbine is 1/16 and the 30-30 is 1/10... but its playtime and i'm bored...i dont want to spend big $$ on a new barrel blank...

Before you do it, figure out the magazine/feeding. I can tell you those sheet metal magazines were designed by Satan himself. The coned breech means the nose of the bullet has to be guided very accurately to feed. And upward at a steep angle. The 30 carbine is close to a 222 case head so you may get it to work with a 222 mag. I very much doubt you will get a 30-30 mag to even hold the ctgs. Check not only the top round but all 3 rounds before you cut anything. I converted a 30-30 to 41 mag and encountered a lot of issues that took me days to resolve. For one, the ctg releases too soon and can jump out of the ejection port (particularly when the mag is full). When the ctg does feed, the bullet nose dives under or to the side of the breech opening and since the cone goes the wrong way, it jams there.

To fix the early ejection you have to block off the rear of the mag, make a new follower, make a new spring, weld up the release cuts, reposition the release cuts forward a bit, and modify the indentations that guide the ctg, even making new indentations. None of this is straightforward.

The other problem you are going to have is the barrel starts to taper just in front of the existing threads. So if you shorten the barrel, there go your threads.

And a 222 mag won't go in a 30-30 action, the opening is wider and longer. So you would need to fix that as well, another headscratcher.

I have a better idea for you: 7-30 waters. I have a (new) barrel blank cut to the right profile I will sell you. This ctg feeds from the stock mag.

Or if you are really brave, you can try the 41 mag. If I were to do it again, I would do a 41 supermag and use pointy bullets (Hornady 300 grain). I think those would feed from an unmodified 30-30 mag. I have a .411 barrel ditto.

my plan is a single shot .30 carbine....using the 340 action i have,,, and switch back to the 22 spitfire as i wish, with just a barrel change...