HDU

From a personal opinion from owning a number of big bores 375 and up
and based on my stock makers thoughts,

300 Win Mag etc etc 1 Cross Bolt
338 etc at least 1 cross bolt
375 and up 2 cross bolts, ESPECIALLY 458 and above.

It also depends on how good the stock job / bedding is.

A badly inletted stock will crack within 5 - 10 shots.

Adding another cross bolt is a lot less expensive than replacing a stock
if it breaks. I have seen people try to save money by skimping on these
things and it ends up costing them twice as much.

Hope this helps

500 Nitro