CassGA
Senior Member
I have a Sig M400 with a 1:7 twist. I have 55 gr .556 FMJ that i have been shooting through it and cannot get it to group at 100 yards. At 25 yards, Im getting sub 1/2" groups. However, if i back up to 100 yards, they are all over the place, with no consistency. Attached is a picture of my grouping at 100 yards. This is from a bench. I have tried 3 different brands of bullets and two different scopes, all with similar results. Are the 55 gr too light? Im going to pick up some 62 gr to try. I understand the twist and that a heavier bullet benefits from the faster twist, but I also was of the understanding that 55 gr would be fine with 1:7. I hope the heavier bullets help but hate that i already have 500 rounds of 55 gr. Any other ideas? Thanks