The MK-85 .50 cal barrels started out with a 1:48 twist in 1985, changed to 1:32 in 1986, and settled on the 1:28 in 1987. These were Patented Accu-Precision premium quality 4140 chrome moly or 416 stainless steel. These barrels have 6 lands and grooves. Once they settled on the twist rates the .36 cal and .45 cal were 1:24, the .50 cal and .54 cal were 1:28.
Green Mountain barrels were not used until later, and have 8 lands and grooves with 1:28 twist in the .50 cal.
Green Mountain barrels were not used until later, and have 8 lands and grooves with 1:28 twist in the .50 cal.