9mm Luger - Windage Drift at 100 yd questions?
- By metroplex
- Semi-Automatic Rifles
- 25 Replies
I know it is silly to ask about spin/windage drift on a pistol cartridge like 9mm, but I have a Vector SBR that has a 6.5" barrel and 1/10 twist. Basically its an overglorified Glock 17L with a threaded barrel. When I zero it at 100 yd and check the laser bore sight afterwards, the laser is way high and to the left of my POA. I'd say about 3"-4" to the left and 6" or more high at 18 yd with the laser bore sight.
Worse, at the 100 yd line I can print a 2.5" 5-shot group but then sometimes none of my shots are on paper. I've tried different optics to no avail. I figure since the barrel is part of the lower receiver, and the optic is attached to the upper receiver that it may have some impact on this. I did notice that after a few shots or a mag is when the shots no longer hit paper at 100 yd. Once it is all cooled down, it seems to shoot normally for a bit.
Strelok does predict windage drift out to 100 yd (without any wind) but its showing a max of about 0.5 inches. Normal rifle cartridges don't show much in the same app.
I can understand the elevation drop because 9mm is a slower heavy bullet (115 gr at under 1200 fps or 124/147 at even slower velocities). But that much windage shift is odd.
I thought my barrel might be bent, so I re-adjusted and zeroed the windage at 7 yd, 18yd, and then checked it with the SL-150 laser boresight at 45-90 yd. It was dead-center at all of these distances. So the barrel is presumably "pointing straight".
Sierra shows 115gr JHP to have 1.15" windage drift at 50 yd. So it could be something like 2" at 100 yd? And given a 2"-3" grouping precision at 100 yd, could that explain something like a 4"-6" drift?
www.sierrabullets.com
Is it just the nature of 9mm fired out of a short barrel at this distance?
Worse, at the 100 yd line I can print a 2.5" 5-shot group but then sometimes none of my shots are on paper. I've tried different optics to no avail. I figure since the barrel is part of the lower receiver, and the optic is attached to the upper receiver that it may have some impact on this. I did notice that after a few shots or a mag is when the shots no longer hit paper at 100 yd. Once it is all cooled down, it seems to shoot normally for a bit.
Strelok does predict windage drift out to 100 yd (without any wind) but its showing a max of about 0.5 inches. Normal rifle cartridges don't show much in the same app.
I can understand the elevation drop because 9mm is a slower heavy bullet (115 gr at under 1200 fps or 124/147 at even slower velocities). But that much windage shift is odd.
I thought my barrel might be bent, so I re-adjusted and zeroed the windage at 7 yd, 18yd, and then checked it with the SL-150 laser boresight at 45-90 yd. It was dead-center at all of these distances. So the barrel is presumably "pointing straight".
Sierra shows 115gr JHP to have 1.15" windage drift at 50 yd. So it could be something like 2" at 100 yd? And given a 2"-3" grouping precision at 100 yd, could that explain something like a 4"-6" drift?
9MM LUGER ~ 115 GRAIN JHP ~ Trajectory Chart - Sierra Bullets
www.sierrabullets.com
Is it just the nature of 9mm fired out of a short barrel at this distance?
