Double Discharges are mostly caused by an inexperienced Double User (or an experiecned user in a hurry !!!)
touching the rear trigger on recoil of firing the front trigger (I DO NOT subscribe to the idea of firing the rear
trigger first to over come this potential problem)
OR
the sear of the rear trigger dropping on recoil of the gun (assuming the gun does not have intercepting safety's).

I have experienced it in a 500/465 - it had done it at the range once when a friend shot it - I made a mental note but
as I had just fired 20 rounds I put it down to touching the rear trigger.
Anyway, the next tme it doubled on me was in front of a large buffalo - I knew the gun had doubled on me but the
recoil wasn't noticeably different - however it did prove that reloading practive makes perfect as I relaoded very fast
and carried on.

Will a double discharge take a gun off the face - probably over time - I wouldn't say that it does the gun any good.

IF you are ever shooting a previously unfired by you double rifle or you ever lend your gun to someone else to shoot,
load only one barrel - saves alot of embarressment if both barrels go of.

"Shooting true solid bullets such as monoblocs and X-bullets is discouraged in
doubles as the bullets presumably do not have enough "give" in the rifling"
- it is the bullets that do not have enough give in them, therefore it is the barrel that has to move more.

I don't think vibrating is an issue but damge to the barrels and WELD between the barrels is a BIG issue
which is why you shouldn't use monoblocs and X-bullets (Barnes).

Hope this helps.

500 Nitro