I've been given a G33/40 mauser action... will this accomodate any of the big bore rounds? Is this a good action or am I better off with an Argentine 1909 for a big bore project?

G33/40 was THE action for custom 270 Win sheep rifles as it is the lightest of all Mauser 98 actions (it was originally produced for German paratroopers). As it is a small ring Mauser 98 with a smaller barrel thread, you are better off using it for cartridges based on 30/06 or 8x57 cases, not the bigger magnum cases.
The Argentine 1909 is a large ring Mauser 98 and is more suitable to be modified for the larger magnum cases.

CMcDermott hit the nail on the head!

I think the G33's are perfect for the 7x57 class of cartridges.

The G33/40 uses smaller threads than the regular large-ring M98, so the ring is about equal thick. I really do not see why any larger round - within limits - should not work properly.
What cartridge did you have in mind?

"What to do with G33/40 action???"
That is an easy one, just send it me (I'll even pay for the shipping so you aren't out anything)and save yourself all the headache and worry. I will have it built into a fantastic little 9.3x62 and then we will both be happy.

Seriously though, good luck with whatever you choose to have built...

Brian

I have one an I plan on a 7x57 or .280 with it...The 9.3x62 is the biggest round I would suggest, but even then I would opt for a standard 98 for the 9.3s...

The G33-40 is just the ticket for a light rifle and the .270 class of cartridge.. A sheep rifle in the making.