Yep, never owned one, handled a few but never examined the action in detail.
I've rebarreled many dozens of Mausers and Mosins, and have a customer that I'm currently doing one for ask me about taking on his 1903 (I believe it's an A3).

I've Googled myself to death, trying to find detailed pics/sections of the action, bolthead/cone breech etc. with no luck. So, other than knowing its 10 tpi square thread- I'm lacking the rest.

Hopefully there are inserts for square threads, or at least pre-ground HSS so I don't have to challenge my mediocre grinding skills.

Can the bolt lug be modified to eliminate the whole cone breech/extractor cut, or is all that extra machining required?

I know there's short-chambered prefits available, but none in the desired .270 (which looks like it should work fine far as I can tell).

Any advice here or link to a resource? Thanks in advance.

Pre-ground square-thread bits are available from Brownells:

https://www.brownells.com/guns...he-bits-prod715.aspx

Don't let the cone breech or extractor cut throw you. John Hinnant's book runs through it and makes it pretty straight-forward.

https://www.brownells.com/guns...itting-prod6915.aspx

At Trinidad, I was the only guy in my barrel-fitting/chambering class doing a coned breech and extractor cut (with a Winchester), and I was intimidated. I was behind all the guys doing Remingtons and Mausers. But now I'm glad that one was the first one I did. A lot more measuring, particularly with feeler gauges.

All that said, I think Krieger was doing a pre-cut and timed 1903 barrel. They were limited run each year and in 30-06. But they might do one in .270.

Hope this helps,
Steve

There should be a dimensioned drawing in the NRA Gunsmithing Guide book.It's a very simple operation.I have a formed cutting tool that was military surplus.It works like a counterbore.I normally just do the cone breech with a lathe bit though.