You may have "several" problems facing you. Have you checked the cyl. throat diameters to see if tight or oversize for the bullits you are using. How about forcing cone angle(11 or 5 degree cut) and depth. Did you range the the gun(bbl align to cyl's). Is there a tight spot where the bbl is screwed into frame. Yes, check muzzle like JP suggests, is it cut square to centerline of bore and undamaged. "IF" bore is .355 diameter, the .356 bullits should work fine. What is the quality of the bbl.? What make? Make sure bbl not cobby and leading up badly.
Try the .356 bullits with the load you like and check the cyl throats and muzzle condition firs.
These are suggestions only and it could be one simple solution or multiple factors. Guns like women, can never figure um out and when you get a good one keep it.(lol)
You mention finely produced 148 grain hbwc's. Who made uM? What diameter are they?.357,.358,359?
With a 1:10 twist bbl. these should work fine.
Again, just some thoughts, hope this helps.