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Posted: 7/11/2008 10:39:49 PM EDT
[#1]
Well, if you zero your rifle at 50 yards you'll have your rifle zeroed out to 220 yards. After that you'll just have to use a "hold over." to be on target. I have a TROY sight and had no issues hitting steel plates out to 210 yards. I was also able to hit a plate, consistently, out to 305 yards, with XM193 and just a little hold over.
The small aperature and the large aperature are on the same plane. The smaller one can be used if you need a bit more precision, which helped me a bit at the 300 yard range. I was using the large aperature for everythign from 220 yards and in. ETA: From the book Green Eyes and Black Rifles (Kyle Lamb, 2008), this is the ballistic chart for for XM193, using a 50 yard zero: 25 yards: -1.12 50 yards: -0.00 75 yards: 0.84 100 yds: 1.39 150 yds: 1.56 200 yds: 0.36 250 yds: -2.33 300 yds: -6.71 |
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Posted: 7/11/2008 11:28:11 PM EDT
[#2]
Awesome thanks for the advice. So I'm assuming by "hold over" you mean at about 300yds I'd have to aim 6.7 inches above target to hit it... How do you like your troy sight? Do you rub it down with some CLP? Is the negative, then positive, then negative on that distance chart due to the arc of the .223 round, and this would be reduced with a heavier round like a .308? How do snipers hit a target at 200 yards and then turn around and hit a target at 1200 yards? |
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Posted: 7/11/2008 11:32:34 PM EDT
[#3]
Yeah, that's what it means, but the book didn't specifiy whether it was a 20", 16" or 14.5" barrel. All I know is that I have no issues hitting the steel plate out at 305 yards with my rifle zeroed at 50 yards.
Nah, I haven't put crap on my sight, just use it as is. Don't get too carried away with the lube. When I had my Bushy with a cut down carry handle, I would use the elevation knob to help me out when shooting to 400 yards, but since the Troy doesn't have this, I just use HOLDOVERS based on the ballistic chart. |
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Posted: 7/11/2008 11:32:57 PM EDT
[#4]
I just got my Troy BUIS lasterday and have yet to sight it in.
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Posted: 7/12/2008 1:53:56 AM EDT
[#5]
This can't be correct. |
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Posted: 7/12/2008 11:38:26 AM EDT
[#6]
Let me double check the book. Hold on....
ETA: OKAY HERE IT GOES: The chart found on page 106 of Kyle Lamb's book, Green Eyes and Black Rifles (2008), was created for a California police department using XM193 ammo. Their rifles were zeroed in YARDS, not METERS. It also stated that the REPEAT ZERO is at 210 YARDS. Once again, I don't know what barrel length that PD used. Velocity, on chart, was 2940, BC was 0.338, humidity was 67%, barometer 29.98 in/HG, sight height was 2.5" and the temp was 64 degress F. In the book it also showed a chart for M855 Green Tip 62 grain ammo. This was done in METERS and had a 50 METER zero included. At 200 METERS it shows the round to be at -1.56" , -5.78" at 250 meters and -12.27" at 300 METERS. Velocity was 2900 and BC was 0.296. Is this crap wrong? If it is, then it's a major oversight on Mr. Lamb's part, which I don't think he would do, as he knows his shit. |
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Posted: 7/12/2008 11:51:50 AM EDT
[#7]
Why can't it? When zeroed at 50, the bullet is still rising. It hits its peak around 175 IIRC, and then begins falling. The reality is it crosses the line of sight again very close to 200, and then from that point out falls below LOS. So when your weapon is zeroed at 50, it's really zeroed at two different ranges: 50, and then the point again where it crosses LOS the 2nd time. |
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Posted: 7/12/2008 11:54:19 AM EDT
[#8]
CORRECT! The second zero, per the book, is at 210 YARDS when using a 50 YARD zero. This why I use a 50 YARD ZERO, because of it's versatility from 0-300 yards, which is what I consider the max effective range of the AR platform. Actually, 250 yards is more like it, of coursse that's depending on AMMO!!!
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Posted: 7/12/2008 11:56:26 AM EDT
[#9]
And here's the BEST 50 yard zero target that I have used thus far, which was posted by MOLON:
50 YARD ZERO TARGET |
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Posted: 7/12/2008 12:27:08 PM EDT
[#10]
So are all rifles plagued by this effect of only zeroing twice on a given range
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Posted: 7/12/2008 12:53:11 PM EDT
[#11]
Yep, unless you can find one that is exempt from Newtonian physics. en.wikipedia.org/wiki/Trajectory_of_a_projectile |
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Posted: 7/12/2008 1:00:03 PM EDT
[#12]
I don't know if plagued is the word, but what goes up must come down......I suppose there is a point in very close range shots that almost stay the same. Like 15 yds and 20 yds but that is pistol range.......
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Posted: 7/12/2008 1:06:01 PM EDT
[#13]
It is. It's actually a 200 meter zero, but good luck finding one of those. By pure luck, the bullet first crosses the shooter's line of sight at 50 yards... hence it's commonly known as a 50 yard zero. |
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Posted: 7/12/2008 1:14:21 PM EDT
[#14]
A 200 METER zero for 62gr M855 yielded this:
25 meters: -1.09" 50 meters: -0.39" 75 meters: 1.32" 100 meters: 1.89 150 meters: 1.83 200 meters: 0.00 250 meters: -3.83 300 meters: -9.83 350 meters: -25.25 A 50 METER zero for 62gr M855 yielded this: 25 meters: -1.09" 50 meters: 0.00 75 meters: 0.74 100 meters: 1.11 150 meters: 0.66 200 meters: -1.56 250 meters: -5.78 300 meters: -12.27 350 meters: -21.36 There's a big difference when using yards and meters to zero, no? |
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Posted: 7/12/2008 2:10:20 PM EDT
[#15]
So what would you guys recommend for a sight (either red dot or telescopic) that has a bullet drop compensator? I really like the GRSC one I saw. Seems like kind of an "all purpose" sight.
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Posted: 7/12/2008 2:21:38 PM EDT
[#16]
Unless you going to be shooting LONG distance you don't really need that, IMHO. Withmy TROY BUIS sight I can hit steel plates out to 300 yards, which I believe more than covers anything you may encounter in a SHTF scenario.
I'm going to get an Aimpoint M3, maybe an M4, with a magnifier some time in the future. It won't have a bullet drop compensator, but I'm pretty sure I can use hold offs to get out to 400-450 yards. What i need though is a ballistic chart for XM193 to figure out what the drops are at those ranges. What you need to ask yourself is this: Is the scope I want for close quarters? Or do I want a marksman optic? I chose the CQB type scope, because that's the role I chose for my rifle. YMMV. Here, read this. |
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Posted: 7/14/2008 5:23:10 PM EDT
[#17]
The rear sight has an elevation knob with range indicators from 300 to 800 meters and two apertures for range. The larger aperture (large hole) may be marked 0-2 for short range from 0-200 meters and an unmarked aperture (small hole) for normal range from 300 to 800 meters.
(1) The 0-2 (large) aperture is used for short range (Figure 107). This aperture is used only when the rear sight is all the way down. The 8/3 (300-meter) mark on the elevation knob is aligned with the index mark on the left side of the receiver. (2) The unmarked (small) aperture (Figure 108) is used for normal range. This aperture is used for most firing situations. It is used in conjunction with the elevation knob for 300- to 800-meter targets. http://www.armystudyguide.com/content/army_board_study_guide_topics/m16a2/zero-and-m16a2-rifle.shtml Hope this helps straighten out some of the aperture confusion! USGILT |
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Posted: 7/14/2008 5:52:21 PM EDT
[#18]
I am new to the AR format so please forgive my ignorance. I certainly understand the ballistics that result in two points of zero but does the height of the target relative to the height of the muzzle make any difference? It seems to me that they should be the same distance off of the ground to be accurate but I am having a little trouble with that part of the physics. Thanks
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Posted: 7/14/2008 11:36:36 PM EDT
[#19]
That's a good point... now that I think about it, I may choose the same route you did because if I want a super accurate tack driver, I'll probably pick up something chambered in a .308... maybe a Remington 700. |
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Posted: 7/19/2008 10:49:10 PM EDT
[#20]
There ya go, now you're thinking. Plus, with an AIMPOINT M3 (with 2 MOA dot), you can add a mangnifier (in a LaRue pivot mount) and kinda have the best of both worlds. It won't be a SHORT DOT, but it'll be good enough. That's what I'm hoping to have in the end. |
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