i use an AR with a 20 inch wilson combat super sniper barrel in .223 wylde. i use federal factory 53 grain v-max, when i do my part it shoots 1/2 inch groups at 200 yards off the bench. only ever had one run off, the rest dropped right there or ran a little ways. i would think 40 grain is kind of light, depending on your rate of twist.
wilson recommends the following
- .223 Remington/5.56mm NATO
1-7: Match or hunting bullets in the 68gr – 80gr range
1-8: Match or hunting bullets in the 50gr – 77gr range (best all around choice)
1-9: Match or hunting bullets in the 45gr – 69gr range