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Posted: 9/8/2003 11:25:30 AM EDT
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On my 14.5" flattop M4gery I have a TA31 mounted on an ARMS 19s. Firing M193. The Big ACOG BDC Chart I need to sight in 1.5" high at 100yds to have the BDC work well. This may be a dumb question but what is the aiming point for a donut reticle at 100y? Top of the donut? Center of the donut? All the sight picture diagrams are done on blank silhouettes with general "center of mass" holds -- not really helpful for precision zeroing. |
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Yes, top of the circle at 100 yards, which will be near the apogee of the bullet's ballistic curve. At 50 yards, it will still be rising, and should cross the center of the circle, and should cross the center of the circle again at around 200 yards, and cross the bottom of the circle at approx. 300 yards. But, remember that these optics are DESIGNED for center-of-mass shooting, not for "precision" in the traditional sense. It was because the traditional design (as used in the TA01 series) worked poorly for field/combat shooting that the BAC-equipped ACOGs were invented. -Troy |
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Quoted: At 50 yards, it will still be rising, and should cross the center of the circle, and should cross the center of the circle again at around 200 yards, and cross the bottom of the circle at approx. 300 yards.-Troy This being the case then is it also true that you can sight the TA31 in at 50 yds using the center of the circle as POI ? |
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As posted by Troy: [b]"At 50 yards, it will still be rising, and should cross the center of the circle, and should cross the center of the circle again at around 200 yards, and cross the bottom of the circle at approx. 300 yards."[/b] Is this true while firing the rifle perfectly level? I was always under the impression that the trajectory of a .223/5.56 round was pretty flat out to 100 yds. What would make the bullet "rise" before then? |
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Green, Yes, you can sight in at 50 yards with the center of the circle, giving you the same zero as the IBZ for the iron sights. Ideally, you'd zero with the center at 200 yards, though, which will tend to give you a bit more accuracy throughout. PPD, All guns have their barrels pointing up slightly when compared to the sight plane. If this was not the case, then the bullet's path would never cross the line of sight. With the zeroing I've described, and assuming the center of the scope is about the same height as the irons, you get a very flat trajectory from 25m out to 250m or so (this will depend on your load selection, of course), with the bullet staying within 2" above or below your line of sight out throughout that distance. [img]www.ammo-oracle.com/images/pathshort.jpg[/img] The blue line gives you an idea of what this zero looks line (it's actually a little off, becaue this graph represents a 250m zero, not a 50yard/220m zero). -Troy |
| I'm wondering now. I just got a TA31 with donut. My thought was the center of the donut was the sighting. If the top of the donut is the true sighting point, then I'm thinking the Chevron (TA31A) is more ideal since the top of the "arrow" or "point" is the true sighting point. More natural to look at the the tip of the arrow than the top of a circle. Any thoughts around this? |
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Quoted: I'm wondering now. I just got a TA31 with donut. My thought was the center of the donut was the sighting. If the top of the donut is the true sighting point, then I'm thinking the Chevron (TA31A) is more ideal since the top of the "arrow" or "point" is the true sighting point. More natural to look at the the tip of the arrow than the top of a circle. Any thoughts around this? Well, true at 100m; but how about 200m? using the TA31A your point of aim is now the middle of a 4 MOA triangle - and the triangle will obscure your actual impact area. At 300m, you are using the bottom of the triangle. With donut you have visibility at all ranges, albeit a slighty less precise aim point since you are using the top or bottom of a circle. You also have multiple aiming points (top of donut, top of donut hole, center of donut, bottom of donut hole, bottom of donut) for reference. I was putting 5-round groups into a 1" colored square at 100yds from a bench - so you can be fairly precise with the donut. You could probably be more precise with the triangle; but there are tradeoffs for that. All of the ACOG reticles are great in my opinion and they will all do a good job for a GP scope. The key is to decide what tradeoffs you want to make to handle the job you plan to do and pick the reticle that best matches YOUR situation. |
| Sighted in at 50yds W/center of donut.It is as mentioned on this board.I'm on at 100yds with top of donut,just like ACOG recommends,but easier done starting at 50yds.At 50yds i could see my bullet holes thru the 2MOA center hole for a more precise sight in i thought, rather than using the top of the donut at 100yds. |
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If you want [i]precise[/i] aiming, you need a scope with crosshairs. Anything else is a compromise. The DoD is, by most accounts, the best compromise for CQB and distance shooting. You can go the way I did and mount the ACOG on a removable carry handle, then have a scope in an Armalite one-piece mount for those "special" situations. You'll never be at a loss with that combo handy. |
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Quoted: If you want [i]precise[/i] aiming, you need a scope with crosshairs. Anything else is a compromise. Exactly. Remember, these scopes aren't designed for shooting itty bitty groups; they're designed for shooting at human-sized targets FAST. It's a different way of thinking if all you've done was shoot for groups, but remember: these are COMBAT optics. Here's a reminder of how they work at various ranges: [img]photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=16681[/img] Remember that you'll be using the ladder for shots beyond 300m, so the shape of the lighted reticle is irrelevant. Note too that the top right-hand distance should read 300m, not 250m. -Troy |
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Following the advise given here I zeroed my TA31 using the top of the Donut at 100 yards. I had initially done the hasty zero shown in the manua, using the bottum of the donut at 25-yards. [b]That put the rounds about 8" High at 100!!![/b] Since the donut retical isnt very precise, i used a target that had an inverted triangle as the bulls Eye. That made it easier to find a consistent aiming point. First 100 yard group from a clean, dry, cold Brl resulted in a 1.21" Group. Group from fouled warm Brl measured .89" With the TA31 sighted in an 100 yards, using the top of the donut, the center of the donut was on at 200 and the bottum of the donut was on at 300. I confirmed that with about 70 rounds fired at steel plates at those ranges. Hits at 400 were a little tougher, and hitting the mountain lion target at the 500 meter line was iffy, only hitting it about 1:3 shots. Cant wait for that NATO spec 77Gn OTM ammo to come in.... |
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Tried the 77Gn Nato spec ammo today. With top of the Donut zeroed for 100M. 2nd horizantal bar for 25M Center of Donut for 50M Top of Donut for 100M High center of Donut for 200M Bottum of Donut for 300M 1rst horizantal bar for 400M My rifle didnt shoot anywhere near as well at 100M with 77Gn OTM as XM193, but hits at 400M were more consistant. YMMV. |
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Quoted: If you want [i]precise[/i] aiming, you need a scope with crosshairs. Anything else is a compromise. The DoD is, by most accounts, the best compromise for CQB and distance shooting. You can go the way I did and mount the ACOG on a removable carry handle, then have a scope in an Armalite one-piece mount for those "special" situations. You'll never be at a loss with that combo handy. What is DoD? Bill |
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