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Pro2AinPA
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Posted: 4/12/2009 12:09:35 AM
I just put a Trijicon TR21 on my AR, and I'm wondering what distance I should zero it at. I'll be using this optic/rifle combo for "run and gun" competitions with targets from 10 to 75 yards out, and for shooting 8" steel plates at 100 and 200 yards. With the trajectory of .223 in mind, is there a distance I can zero the optic at that will give me good results for everything I intend to do?
hmaverick
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Posted: 4/12/2009 12:13:44 AM
50 yds
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Pro2AinPA
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Posted: 4/12/2009 12:14:43 AM
Originally Posted By hmaverick:
50 yds


Where would that put my POI, roughly, at 100 and 200 yards?
hmaverick
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Posted: 4/12/2009 12:17:20 AM
im no expert, but i think that puts the round nearly on at 200 and a little high at 100... i think... standby for someone with a ballistics chart
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bada61265
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Posted: 4/12/2009 12:21:34 AM
i think from memory its 50 yard zero less than half inch low at 200 2" hiigh at 100 .
Combat_Jack
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Posted: 4/12/2009 12:22:48 AM
200 meters.
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hmaverick
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Posted: 4/12/2009 12:27:27 AM
[Last Edit: 4/12/2009 12:28:47 AM by hmaverick]
i would think that if someone were to help, they would need the centerline height of the tr21 above the bore and also the grain weight and bbl length. also, a chronograph would help.

but from what i've been reading, 50 yds is pretty all purpose, unless you have a bdc reticle

eta: then again, the guy with 43k posts above might have some useful knowledge,

i would be concerned that in a 200 meter zero, youd be high at everything shorter... especially your close up shooting
Brian Fantana: That was one crazy party. I am hung over.
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Combat_Jack
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Posted: 4/12/2009 12:44:27 AM
50/200 are very close. IIRC 50 puts you 2" low at 200. I prefer a 200m zero.
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TENN
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Posted: 4/12/2009 1:41:50 AM
50 yards
Socom529
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Posted: 4/12/2009 2:34:37 AM
50 yrds, so I was told.
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Posted: 4/12/2009 3:47:49 AM
50. Very close at 200.
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M4builder
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Posted: 4/12/2009 8:05:58 AM
50/225 meters = -3" @ 300. w/ a 20" barrel w/ M855. Not much different with a 14.5" (-4" or -5" @ 300 meters).

Someone correct me if I'm wrong, it's been a while.
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socommatthews
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Posted: 4/12/2009 9:07:38 AM
I zero'd the tip of the triangle at 50y. That way your not off more about 2" out to 200. For you, 10-75, 50 would be great because it would only be maybe .5" high at 75y and at 10 hell just use the whole triangle as a dot and your set.
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RIFLEMANIV
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Posted: 4/12/2009 9:21:40 AM
For iron sights if you zero the rifle 1" low at 25m you should be dead on at 200m. That works out to be .5" high at 50m, 2" high at 100m and 10" low at 300m. Not sure how this translates to an optic but I would think it would be close. Also that ballistic info is for the 62 grain M855 round.
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Fresh2Salt
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Posted: 4/12/2009 11:45:54 AM
I've heard all the same. 50yrds is close to 200yrds.
MikefromTX
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Posted: 4/12/2009 12:19:06 PM
^ Agree. All the ballistics charts I've seen show the 55gr .223 will be about 1.9 - 2.0" low at 200 yds. when dead-on at 50 yds.

Google .223 ballistics to see for yourself.

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uvausmc
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Posted: 4/12/2009 12:45:19 PM
go here, put in all your info, figure out where you want it zeroed

http://www.biggameinfo.com/BalCalc.aspx
Belmont31R
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Posted: 4/12/2009 1:23:59 PM
Zero at 50 yards, and within a reasonable range your rounds will never be more than 3-4 inches different than your sight picture. If you zero at 25 or 100 its going to be much further off. Basically you want a gun you can put the dot on the target, and be able to hit that target without a hold over or hold under. Just point and shoot, really.


Here is a chart that shows a typical bullet drop with a 50/200 yard zero:




Here is one that shows a 25 yard zero:




While the 25 yard zero is closer at 300 yards the bullet path is far more different than the line of sight over the entire range from 0-300 yards. You would need to hold under to get accurate hits through the range.


Illustrated version of the above statement:

50/200YZ:


25YZ:




This would not apply to scopes with built in ballistic drop compensators unless you didnt want to use the BDC feature...
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Belmont31R
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Posted: 4/12/2009 1:26:58 PM
Forgot this too....


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MSPRet
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Posted: 4/12/2009 1:42:40 PM
[Last Edit: 4/12/2009 1:47:21 PM by MSPRet]
I have read the Marines sight in thier rifles at 33 meters (appx 35 yards) for thier BZO while the Army uses the 25 yard BZO. Thanks for the charts, this has been an interesting thread. Do you have the same charts for a 33m/35 yard zero? It seems that the 33m/35 yard BZO might be the optimum range to sight in for the coyote hunting I do with my AR's, rather than to sight it in at 1.5"- 2" high at 100 yards as I do with some of my other hunting rifles...Thanks....<><....:)
slammer11111
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Posted: 4/12/2009 2:50:23 PM
Yeah, we did zero in at 36 yrds in the Corps. I was a rifle and pistol coach there. What we were taught and what we taught was that a zero at 36 yds was for 300 yds. I never saw any of the charts though, they provide the visual that I was looking for when I tried to explain it to shooters. I never really got into all of the physics of it though. If my shooter was aiming center mass and hitting low on the actual range and not on the BZO range, I'd have them do a read sight adjustment.
defconfive
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Posted: 4/12/2009 3:47:17 PM

Originally Posted By uvausmc:
go here, put in all your info, figure out where you want it zeroed

http://www.biggameinfo.com/BalCalc.aspx

Nice resource.
MSPRet
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Posted: 4/13/2009 11:59:49 AM
Thanks Slammer, that go's along with what I had heard, Army @ 25 yds / 200 yards and the Marines @ 35(36) yards / 300 yards....<><....:)
Pro2AinPA
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Posted: 4/13/2009 12:01:29 PM
I zeroed it at 50. It was extremely windy so I didn't bother shooting any farther out.
USMC-Helo
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Posted: 4/13/2009 1:06:39 PM
[Last Edit: 4/13/2009 3:14:30 PM by USMC-Helo]
When I shot on the Range Active Duty in the Marines, we used A2's and had elevation adjustments, which also complicates the "understanding" of the zero somewhat.

Leaving elevation adjustments out of it, for simplicity.

If I understand it correctly, your sights/optics are setup to fire the round on an arc (its going to travel a ballistic arc no matter what you do) but its aimed upwards just slightly. SO, when you zero you sights, it will be dead on for 2 points on the arc. Where you zero your sight, will determine what 2 distances those dead on points will be, and how the other distances will vary in elevation at the other points. i.e. 50/200 meter will vary less in elevation than 25/350 meter OR 36/300 meter, except when you get out past 300 meters and then it drops off more rapidly.
MillerSHO
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Posted: 4/13/2009 1:51:22 PM
Great thread
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