With the powders that are most suitable for the .450, no. Most full loads for the .450 are compressed to one degree or another or nearly so, therefore until you can increase case capacity, you are already pretty much at max. The length of the action and magazine prevent loading to a longer overall length. Were you using the larger .45-70 case with stronger actioned rifles, then can you see some advancement. As much as I like BLR's (have 3) I have never seen why they bothered to list that chambering unless some folks just like the rifle or have to have the detachable magazine.
Now, a custom long action BLR with an 18 inch barrel in .458 could have some possibilities.