Just came into an extremely cheap Ruger left hand 77 with 18 rounds through it, broken stock, plus new stock from Ruger. Intend to reinforce new stock, but want a different caliber. Currently have 7mmRemMag, 7STW, .338WSM, .395Max, and .450Marlin plus many in the smaller calibers. Any suggestions in the bigger bores? Must fit in this action.

Prof, what caliber is this one in?

Look at the 458AccRel. Goes mild to wild Clint

Ditto on the 458 AccRel. I love mine. 458WM is ok, but the 458AR is nice because of the shoulder and its versatility allows it to do anything you want.

Max,
Is it a CRF Mk II M77?
And please do tell what the factory chambering is.
Sounds like you might sensibly want to expand
your horizons to a 470 or 500?

Guys, thanks for the replies.

RIP: It is a CRF and in .300WinMag. Yes, expanding my horizons would be good. I had talked to Michael about a .470 a year ago, but got caught up with the work on my BLR.
Your work on the .500 also interests me. I want to keep the cartridge short enough to work through the magazine and not require radical work for reliable feeding. (Some work is usually required, though.)

Good platform for a lot of possibilities.
3.4" box length will work for 12.7X68 49-10 except for a few pointy-long bullets
but even those could be single loaded.
Then only 2 down in the box, unless you find a drop floor plate
to fit the Ruger.
Same thing for the 500 AccRel.
There are .475-caliber and smaller opportunities galore
that will go 3 down in the box with no new bottom metal required.
Just some modifications and fine tuning and reinforcement
of what you have there.
AccRel, B&M, or your own pet wildcat on the .416 Ruger necked up to .458.
That would be the ".458 Ruger Max" biggest brother to the .395 Ruger Max.
Has no one done that yet?
Should equal or exceed .458 Lott.
Max on the Ruger case.
Slick in the Ruger M77 MkII.

RIP: Good ideas. I would like three in the magazine. My BLR only holds two in the magazine and one in the chamber (oh the horror of not being able to load two in the chamber).
Of the .470 calibers, I may have to do some more research.
If I went with the .458, I'd probably go with the American classic, the .458Win.

there isn't any flies on a 458 WM. and with the work Michael has done you drop down to the new CEB/NF bullets and you have one heck of a cartridge-IMHO

SSR

Cross makes a good point. Seems like you got most everything covered. I would just trade the Ruger and the 7mm STW off on a new Winchester .458 Win Mag. although I am not sure it will give you much more than your 450 Marlin. The new winchesters seem to be pretty nice.

Yep,
No dramas over the .458 WinMag with new powders and
new bullets giving it 2 legs up.
And it would make a slick 4-shooter in the Ruger.

500 AccRel
.500" Ripper/BUM/12.75x68or whatever the name is today
416 Ruger
458 or 470 AccRel

Like "The Artist Formerly Known as 'Prince'"
there is only one true name,
and no extra digits or punctuation allowed:

12.7X68 49-10

458 or 470 ar fits that platform easily

Max,

You could go with the new 500 B&M that Michael is having the finish reamer and gauges made for right...it'd be perfect for the M77.

And you could have Hornady manufacture the reloading right now while the reamer is being completed. All that would be needed is for Michael to authorize Brian to send Ben Syring the reamer spec's and the reloading dies will be ready about the time Brian is ready to rebarrel your rifle.

On the Ruger platform, since this is a medium-long length action, your most efficient cartridges would be

500 AccRel (or it's sister the 49-10)
or
458 AccRel

The 500 would need minor bolt/extractor work for the Rigby case head.

Those cartridges above will match the ballistics of the 500Jeffrey and the 458 Lott, which will give you a little extra knockdown power than a 458WM or 500BM.

416 Ruger, it fits doesn't it?

How about the .425 Express. It is the .300 Win Mag case opened up to accept .423 bullets. It was designed by Cam Hopkins and the first rifle was built on the Ruger 77 action.

Again, thanks for the ideas. I'm in the process of now researching several of the cartridges mentioned above. From that, I'll make my final decision. The help is appreciated.
Max