Since you say these are the standard 1 oz load I assume they are not hanging right around the speed of sound for the velocity but are well above it. Crossing that barrier can make a tremendous difference in the sound. I have noted this on occasions when firing standard velocity .22 LR's. These are sometimes loaded to just about equal the SOS. Often you can fire them & pick out the rounds which went just over those which were just under. Those just under are like a healthy Spit, & those just over have a distinct Crack.
As a general rule a shorter barrel will produce more muzzle blast as the gasses have a higher escape velocity. Assuming these loads are supposed to give 1200 FPS or more velocity a 27" barrel should not drop that enough to make the sound barrier of importance. From memory I recall that is down around 1115 FPS.
If you can do it conveniently though a Chronograph test would prove that one way or the other. Beyond that I simply have No Idea.
