For bolt-action big bores we know that crimping is a must. What do most of you guys do when it comes to loading ammo for your doubles? I am speaking specifically of bullets with canalures.

I use a medium crimp in the canalures for 465 H&H and 470.

465H&H

Crimping prevents bullet movement ,important in a bolt action. But it also permits proper combustion of powders especially the slower burning ones. My experience is more with things like 44 mag revolvers where lack of crimp and lack of proper grip of the case on the bullet will definitely prevent proper combustion and this also effect accuracy.

I always use a meduim/heavy crimp on my 500NE rounds as well as any other heavy recoiling round used in a multi shot rifle. It prevents bullet jump in rounds after the first shot. Of course it isn't required in single shots, but to be consistent I crimp everything.

I never crimp double rifle rounds. Without adequate neck tension, crimping won't reliably prevent bullet movement under recoil in the off barrel. With adequate neck tension, crimping isn't needed. For the larger bore doubles, just get a smaller expander ball or eliminate it entirely. Nothing more is needed.
------------------------------------------------
"Serious rifles have two barrels, everything else just burns gunpowder."

I definitely crimp all my .470 loads, particulary if they are used for hunting. Crimping also changes the way a load will shoot. I've found that I need less powder in a crimped load to get the same bullet speed of an uncrimped bullet.

Don't crimp for my doubles in .350 Rigby No. 2 or .500/.450. Always ensure that the bullets are seated at least a quarter of an inch into the case.
Regards, Tim