Greg,
What they said. Plus, a few things to check...
First, make sure the brake is snug and hasn't loosened up.
Next make sure the bullet isn't grazing the brake on egress.
Correct either of those problems.
If everything looks good, then you might want to remove the brake and verify that the gun still shoots as expected.
Make sure the crown wasn't damaged during installation.
Perhaps the action screws didn't get torqued properly or the scope is loose from the install procedure?
Make sure the barrel is floated properly.
If the gun shoots fine without the brake, inspect the brake more closely and see if the bore needs to be opened up a tad.
Let us know what you find.
-- richard