This was the Hornady 125 grain XTP American Gunner load.
Pretty dang fast. Out of a 4 5/8 barrel, it was getting 1540.
I prefer heavier for caliber bullets but had just acquired a 686 and wanted something other than .38 Special to try so I bought a box.
Once I gathered dies and components, I've stuck to 158 and 180 gr. bullets.
Those I carry when up in the national forest for 4 legged critters.
For anti personnel, I've been carrying the Remington 125 scalloped HP but in .38 +P.
Super accurate out of the 66-8 as well, and with my vet discount they were $31 per box of 50.
I haven't chronographed them yet but they are not wimpy, and for sure much faster to get back on target than a 1500 fps. load.
I chose a military career while my older brother chose law enforcement.
Not too long into his career he had an encounter where he killed a guy, using his M66 and the Remington 125 grain load being discussed here.
He was on the SWAT team at the time, also training for the National Police championships coming up. He ended up winning the Nationals that year in the 70's, so yes he was a good shot.
He kept his SWAT gear in a duffel bag in the back of his Corvette which was parked in a well lit parking lot just below his apartment. There was a folding stock 870 in the bag with a full magazine of buck, chamber empty.
He had just got out of the shower when he heard glass breaking in the parking lot, grabbed the M66 and walked out onto the patio.
He saw a guy reaching into the back of the car, and he yelled "Halt Police"!
The guy was already in the gear bag and came up with the 870, racking a shell.
As he was raising the shotgun, my brother fired the first round at him, but he was turning and autopsy showed the 125 gr. blew up on the guys upper arm bone and did not reach the chest.
Not to worry, more were headed his way, and the autopsy showed that the guys heart was pretty much non-existent.
Shredded into nothing.
The guy was in no shape to do further damage but he managed to crawl 75 feet still clutching the shotgun before he died.
Autopsy also showed that the guy had a lot of PCP in him.