I have had two model 51s and a no dash 651. The most accurate round in all 3 was the Winchester 40 gr hollow point load. All were accurate although the 651 was unusually so. Frequently under an inch at 25 yards with the Winchester ammo. Never chronographed any of them. I used them as companion sidearms when big game hunting and enjoyed their size, weight and the small amount of space a box of 50 shells took up in the day pack. Eventually I retired them in favor of a 3" pre lock 60-10 in .357; same size, pretty much same weight. Ammo weighed more, but the bigger hole it left in things was important to me due to living in brownie country at the time. I usually had a .338 mag, 9.3x62 or 45-70 along when hunting. If just hiking or stream fishing, I would usually carry the 45-70 SRC Browning and either one of two model 29s or a 10mm Delta. Although those 6/51s were accurate, they seemed to be just as loud as the 60-10, and loud noises don't impress brownies. I kind of wish I had kept the 651 4". It shot so darn well. Every S&W rimfire revolver I've ever owned dumped empties easily until I began using Break Free CLP. Then they started getting sticky and occasionally needed to be poked out with a cleaning road, one at a time (please don't pound on the extractor rod). I'm not sure if the BF is indeed the cause, but I have been told it can get gummy with age. I'm guessing that Ed's Red might work better.
Best, Dave