Must a CZ 550 used in a McMillan CZ express stock be glass bedded? Or can it be shot as is? I have several other McMillans, including one in 9.3x62, that I haven't bedded and they shoot fine. The 550 I am considering would be a 458 Win Mag; I have the stock already and it has their "magnum" fill. Can it be done? Or am I risking damaging the stock?

Bedding fills in any gaps . Gaps = running room . You don,t want to give a 458 any running room if you want to enjoy shooting it much .......... ..

It,s almost like asking if a plywood sheathed roof will leak if it isn,t shingled or in some other way totally waterproofed ....... It will only leak if it rains .. Your stock will only break if you shoot it ...
A friend has a custom shop 416 Rem Mag with the Mcmillion stock on it , no 2nd recoil lug , it broke it,s stock . Factory installed .. Your drop in probably has more gaps,play and the 458 tends to have more recoil .... I,ve seen a few McMillan stocks that broke due to recoil over the years ...I think all were because they didn,t have a 2nd recoil lug under the barrel that was bedded tight ....

On something like that, the cost of having it bedded isn't much compared to the overall cost of the rifle. I most definately have it properly bedded, just for the peace of mind. ON the McMillan it probably won't take much, since I'm sure it fits close already, but still I would want the extra assurance.
KB