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Posted: 8/27/2006 5:39:46 AM EDT
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Background: I'm setting up a Bushmaster carbine for an IPSC rifle match, where most stages have targets between 5-50 yards, and most of those between 10-25 yards. My idea was to set the zero at 25 yards. There is also 1 stage with targets at 200 and 300 yards, but nothing between 50 and 200 yards (range limitations). I put on a new Aimpoint ML3 with LaRue mount (standard height, no cantelever) on the Bushmaster rail (A3 configuration, free-floated handguard) and zero it at 25 using Federal American Eagle 55 grain rounds. I then move out to 50 yards and observe that it groups about 3" high. I now go to 200 and 300 yards, and I get strange results. At 200 yards I'm grouping at least 12" high, and at 300 yards I'm still 8" high (OK, at 300 yards I'm not sure the term "group" is exactly accurate, but it is a red dot  ). Essentially, I have to aim at the bottom of an IPSC target to get A zone hits. That's only a 4" drop between 200 to 300 yards, and certainly way high at 200.My previous experience was with a different gun, using a scope, with a 50 yard zero. My next step is to move the Aimpoint to the other gun and zero at 50, put a scope on the Bushmaster and zero at 25, and repeat the entire test. Is this kind of performance to be expected with a 25 yard zero? |
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I would use a ballistic calculator to figure out the optimal zero and hold-over (eg, you can zero for distance X using the top edge of your reddot, giving you a zero of distance Y when using the bottom of your dot. Height over bore and ammunition would be the determining factors of these two distances here). This zero works very well, you can find an excel based calculator on the same site (might have to apply for membership for downloads access, but that's fine as it's free). |
Yes, which is why we don't recommend it. Nothing strange at all - you'd know this if you ran the trajectories before zeroing at one of the online ballistics programs. Keep your zero at 50y and lean about 'hold over'. Aim about an inch high at tagets 25y and closer. |
A 50 yard zero it is. Now, gotta work on that 300 yard "group." Thanks to all who replied. That's why this forum is so great, plenty of people with lots of experience. |
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