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Posted: 12/31/2013 5:19:41 PM EDT
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I'm having some issues with a new build. I went and tried to sight it in earlier today. I had trouble getting it on paper at 50 yards so I checked over the barrel, the rings and the scope and everything was tight so I pulled back in to 25 yards and found that it was very low. So low I had to max out the elevation and was still 1 inch low at 25 yards. I checked the crown and the muzzle brake but there are no obvious issues with them. Also once adjusted up it put 10 rounds in a 1/4 inch hole so it isn't shooting eratically. Any ideas? This is the scope. It's the illuminated model. The rest of the gun is PSA parts from a couple of years back including a free floated 1/7 fn marked 20 inch chrome lined barrel. The scope is mounted with a larue lt104. The muzzle devices is a mickulek brake. |
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Quoted: Is the LT-104 entirely on the receiver, or is part of it out in your rail? Any slight height difference between the receive and rail slots can have a profound difference in your elevation adjustments. Also, could you post a photo of the setup? |
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Quoted: 1" low at 25y should be high at 50y. Sounds like you have enough elevation for a 50y zero at least. |
| Forgive me for stating the obvious, but it is looking like the upper receiver and your barrel are not parallel. You could try a different scope temporarily in the LT-104 just to rule out the scope, or a different mount just to rule out that, but I doubt it is either. Next I'd try moving the mount to different slots on that rail. What is the paint or coating between the rail snd the LaRue clsmps? If it is not uniform thickness it may be contributing to the problem. Access to a laser bore sighter could also help you in setup as you make changes. |
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OP, is the Larue mount a 20 MOA mount? Granted, that's only 5" at 25y, but no idea what your other variables are.
Sure you aren't having height over bore issues so close with an optic? I know a different target is required to get a 300yd zero with an ACOG. Maybe that's the problem? Throw some iron sights on it and see if they zero? EDIT: Either way, you don't want a zero at the end of the scopes travel. You'll also probably want a 300yd zero, to keep your shots as close together as possible. 100yd would probably be fine if you are doing come-up adjustments manually. Otherwise 300yd Z should keep all the shots close enough for varmits/man sized targets. |
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Quoted:
take the handle of a screw driver and gently tap the top of the turret . some times the erector will stick especially if you have bottomed out or topped out the adjustment . trijicon reccomends you do this when adjusting an acog to help seat the adjustment . Not terrible advice, but more for minor adjustments. If you have travel, and just not enough, I don't think this will help you. To avoid using a too-big of a screw driver on your scope, I suggest tapping with an empty casing. Before, and after each adjustment. If you do manual come up adjustments with your turret, I suggest always loading it to the positive when you retun to your Z. |
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As stated it isn't a 20moa mount. The gun is coated with tungsten cerakote. It's very thin and as uniform as is possible with a coating. I do want to do a 50yd zero which may be possible but as stated is pointless to have when it's at the end of a scopes range. I don't see any obvious signs of misalignment that was mentioned but maybe I'm overlooking it. What picture were you saying made it look that way? I'm going to swap scopes mounts and guns to try to find the culprit now and go from there.
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something is obviously physically wrong. If you built the upper try taking the barrel off the upper receiver and checking the end of the receiver for squarness to the bore. Great thing to do on a accuracy build. Sometime a burr can throw things off. Maybe even hit the end of the threads on some sand paper on a flat surface. brownells has a lapping tool for about 35 that should help. |
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Quoted:
OP, not to insult your intelligence, but is the scope new or was it used on a previous build? I would try returning the reticle back to center, factory zero, and go from there. This. Return elevation to the mid point before going further on this rifle or in a swap. Get or borrow a laser boresighter and check to see how far off you are. Laser should be bright enough to be visible at 25 yards in dim light. I am not a fan of applied coatings on the rail. Only a few thousandths of an inch in difference in coating can be a big difference in point of impact down range. |
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