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Posted: 3/15/2007 7:13:14 PM EDT
| Anyone have any idea the cause(s)/cure for vertical stringing of shot groups--no windage error, but shots stacked vertically. Example: five shot, two inch vertical stack at 50 yds with 1/2 inch total horizontal dispersion from sandbag rest. Group looks faked but I couldn't shoot that kind of group if I tried. Doesn't happen every time. Loose upper/lower? Installed a "wedge" and haven't seen the problem in a couple of sessions so that might have fixed the problem permanently. Local AR "experts" have posed some theories that even I know aren't reasonable, but haven't found a genuine AR expert shooter to pose the question to. |
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If you can, mount a laser on your rifle, and have a spotter watch it on the target while your firing. It dosen't need to be set to point of impact, just to where the spotter can observe movement during the sighting - breathing - trigger pull - follow through steps. The laser can show what may be happening with you while firing. I place the dot about 4" to the side, and after the first group, I put a circle where the dot hits when the shooter has a good sight picture. If the dot sits still, and the group moves, it is the weapon. If the dot is moving up and down, it's breathing. If the dot jerks/bounces in the direction of your stringing problem upon firing it's trigger control. Some movement of the dot will occur from recoil, but it shouldn't move much. A couple snap caps in the stack will be the tattle tails, as the shooter will not realize what is going to happen and react the same as live rounds. That is where you will really see what is happening with the shooter. |
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In a traditionally stocked rifle verticle stringing is usually indicative of a bedding problem. If your AR doesn't have a freefloat handguard then you may not be returning it to the same point on the sand bag. If you're using a sandbag.  If you're using a bipod then maybe you're not getting settled down into the same postition after seach shot.Overall, something about what you're doing is not consistant from one shot to the next. |
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Have done a little more reading since original post and found a reference to "vertical stringing" in Joe Poyer's book on the AR-15. He claims that at least one cause is sloppiness between the upper and lower at the aft take-down pin, and recommends the Accuwedge to tighten up that connection. Bought the piece NIB from a reputable dealer but on take-down for initial clean-up found a wedge already installed, so suspect it wasn't as new as advertised. Left the wedge in and saw the problem occasionally from the get-go, but not recently or at least the last 2-300 rds. Joe Poyer apparently isn't too well thought of by some folks in here, but I have found his book basic and appropriate for a new AR shooter--like me. Thanks, everyone for the suggestions. |
Slop has NOTHING to do with it accuwedge is worthless I had a Bushmaster 20 hbar that shot ragged holes at 100 yards it had play between up and low |
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I read something about using a Rifle stock on a Carbine upper causing early bolt unlock. I only say this because I have put 1200 or so rounds down range with my Carbine without a problem. The other day I fired maybe a 100 or so rounds using the Rifle upper and was getting vertical stringing. Well I started looking at my setup and found the front scope ring was so loose you could turn it with your fingers. They were set to 35 inch pounds and are 125.00 rings not junk. I think the setup must of vibrated it loose, Thanks,Keith |
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