I've owned a couple of M27's and a few Highway Patrolman models (28) and they shot quite as well as a Colt Python I had. At 25 yards, offhand, they would shoot within two inches, if I did my part. From a braced sitting position, they were fantastic.
Remington's 158-grain JSP and JHP ammo seemed to be their favorite. These guns all had six-inch barrels, save one with 6.5-inch bbl. I also had a recent (1990) five-inch M27, but it wasn't as accurate.
Lone Star