Author Topic: Zero for KD  (Read 2246 times)

Offline mjkten

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Zero for KD
« on: March 06, 2015, 02:24:14 AM »
I must be almost done with RBC questions, but one comes to mind...
Should I have my 20" AR zeroed at 25m before I arrive? Right now it's set a little high at 100.
I've read that part of the transition from 25m to the longer distances involves showing how the 25m zero is good to 200.
Thanks,
Mike.

Offline 509gman

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Re: Zero for KD
« Reply #1 on: March 06, 2015, 03:16:43 AM »
Don't RBCs start at 25? If you don't have the fundamental skills to make rifleman down at 25, you'll be using up a lot of expensive bullets trying further out with wind calls and such to contend with.
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Offline mjkten

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Re: Zero for KD
« Reply #2 on: March 06, 2015, 05:59:12 AM »
I made Rifleman at 25 meters with my 10/22.
My question has to do with moving on to the longer ranges with the AR.
And I understand the RBC starts at 25. But I expect to shoot the 22LR there the majority of the time.
What I don't know is whether the move to longer ranges begins with shots at 25m for the centerfire rifles, or what?

Offline 509gman

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Re: Zero for KD
« Reply #3 on: March 06, 2015, 06:05:36 AM »
I haven't been to an RBC but I would expect that the instructors would highly suggest that you shoot the rifle you'll shoot at full distance throughout the course if you can stomach the ammo expenditure. There's a whole lot of growing to do, stepping up from a.22 to a centerfire. Heck, just switching rifle models! But if you insist on only shooting the CF at distance, I think they start off zeroing at 100.
"What! what! men, dodging this way for single bullets! What will you do when they open fire along the whole line? I am ashamed of you. They couldn't hit an elephant at this dist-"
Last words of Union Gen. John Sedgwick, before he was killed by a Confederate sniper.

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Offline DEH

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Re: Zero for KD
« Reply #4 on: March 06, 2015, 07:05:27 AM »
RBCs do start at 25 meters.  If your rifle has standard M16 type iron sights then yes, it is supposed to be zeroed at 25 meters.
Optics throw in some more variable depending on what type of optic you have.
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Offline SteelThunder

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Re: Zero for KD
« Reply #5 on: March 06, 2015, 09:44:12 AM »
The direct answer is:

Show up zeroed at 25 M.  KD will typically confirm zero at 25.  Then you'll move to 100 and use IMC to find your zero there.  Then you'll zero at 200, 300, 400 to develop your come ups and your rifle data card.

At least that's how I run it.  YMMV depending on the exact Course of Fire the SB uses.
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Offline jmdavis

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Re: Zero for KD
« Reply #6 on: March 06, 2015, 10:03:26 AM »
Bring your Rimfire and your Centerfire. You will do alot of work at 25m. You will also have chances to zero at 25 with your Centerfire. There is no need to shoot the Centerfire for the entire week, unless you really want to. There is certainly nothing wrong with showing up with zeroed rifles. It makes the process easier for everyone. But it is not necessary.

Make sure that you have at least 3 magazines for the centerfire. Personally I prefer 20's but 30's are just fine. While you only need 2, a panic mag can help if you have a mag related failure. Also bring cleaning gear. An RBC tests equipment. It REALLY tests equipment.

Since Ramseur has a separate KD range and it's firing line is common for 100-500. Your first shooting there will likely be confirming your zero at 200 or 300 yards. A zero with a 20" A2 is good to around 300 yards. You will likely then shoot some sighters at other distances.  After that you will do a KD Aqt and have an opportunity to shoot popups and steel at various ranges out to 500. It is a GOOD time.

As DEH notes optics do throw in some more variables depending on the system. But it's not a big deal.
« Last Edit: March 06, 2015, 10:06:36 AM by jmdavis »
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Offline JL

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Re: Zero for KD
« Reply #7 on: March 06, 2015, 11:08:13 AM »
mjkten,

Not to overwhelm you with too much data, but for the Known Distance (KD) portion of your IBC, don't forget the standard come- ups we teach at every AS.  If you are zeroed in at 100 yards with your AR15 when you arrive, then you have all the data you need to transition to the 25 yard line. The two important things to remember are that for your AR15, the 25 yard zero and 300 yard zero are approximately equal, and the standard come-ups tell you that to compensate for the bullet drop that occurs between 100 and 300 yards you need to put in a 4 MOA correction, (100>200 is 2 MOA, and 200>300 is 2 more MOA). 

If you were bringing a .30 caliber rifle, then your 25 yard zero and 200 yard zero would be about equal, and the standard come-ups would be 2 and 3, (5 total). 

So, put that all together and you realize that if you start with an AR15 with a good 100 yard zero, you can put in a 4 MOA correction to derive a 300 yard zero, (raise the rear sight to raise the POI), and you will be darn close to being spot on at 25 yards.  That is exactly what I did when I attended a KD event last summer with two rifles both zeroed at 100 yards and it worked like a champ.  It also really illustrates that the theory in the KD section of the AS manual really works. 

Have fun at the IBC!
JL

Offline SteelThunder

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Re: Zero for KD
« Reply #8 on: March 06, 2015, 11:20:42 AM »
mjkten,

Not to overwhelm you with too much data, but for the Known Distance (KD) portion of your IBC, don't forget the standard come- ups we teach at every AS.  If you are zeroed in at 100 yards with your AR15 when you arrive, then you have all the data you need to transition to the 25 yard line. The two important things to remember are that for your AR15, the 25 yard zero and 300 yard zero are approximately equal, and the standard come-ups tell you that to compensate for the bullet drop that occurs between 100 and 300 yards you need to put in a 4 MOA correction, (100>200 is 2 MOA, and 200>300 is 2 more MOA). 

If you were bringing a .30 caliber rifle, then your 25 yard zero and 200 yard zero would be about equal, and the standard come-ups would be 2 and 3, (5 total). 

So, put that all together and you realize that if you start with an AR15 with a good 100 yard zero, you can put in a 4 MOA correction to derive a 300 yard zero, (raise the rear sight to raise the POI), and you will be darn close to being spot on at 25 yards.  That is exactly what I did when I attended a KD event last summer with two rifles both zeroed at 100 yards and it worked like a champ.  It also really illustrates that the theory in the KD section of the AS manual really works. 

Have fun at the IBC!
JL

All sage advice.  Only thing to add is "KNOW YOUR RIFLE".  The standard come ups we teach are a starting point only.  Depending on YOUR rifle, YOUR ammo, YOUR conditions at the shoot, it may behave very differently.  My 20" White Oak DCM AR with 55 gr FMJ over IMR 4064 doesn't behave like our "standard" comeups tell me it should. 
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Offline PHenry

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Re: Zero for KD
« Reply #9 on: March 06, 2015, 03:40:31 PM »
Please see the attached doc for zeroing AR rifles. The rear drum on the A2 is actually a "bullet drop compensator" dial intended to offer proper come ups when using "ball ammo". Originally designed for the M16A2 shooting M193 55gr FMJ rounds. The numbers correspond (roughly) to meters.

The RBC begins with instruction at 25M and eventually, after a classroom session, moves to full distance. You will want to know where the rounds hit using your 25M zero. Different SBs use different COFs, but they all begin with a 25M zero. In fact, at Ramseur, a verified 25M is required prior to heading to the KD range.

Don't worry too much over anything other than bringing your gear, plenty of "food" for your rifle and a teachable attitude. I guarantee you will exit the RBC with a much enhanced understanding of your rifle.  O0
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Offline cdavidhord

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Re: Zero for KD
« Reply #10 on: March 06, 2015, 06:12:26 PM »
Start the RBC with a 10/22 and fine tune your steady hold factors and six steps to fire each shot.  After you perfect your technique by achieving consistent rifleman scores on the AQT, zero your AR15 at 25 meters at the end of day 2 or the morning of day 3.  With that setting, shoot the full size target at 300 meters using the techniques you've polished.  You will be on paper, and can fine tune your 300 yard zero to move your group to the center.  You will then determine the come ups for 400 and come downs for 200 and 100 for your particular rifle and ammunition.

The first time I did this, I used my AR15 (14.5 inch barrel with 1.5 inch flash suppressor, TA31 4x ACOG, with PMC bronze 55 grain) and only had to make less than 1.5 MOA adjustments  to elevation and windage at the 300 yard target.

I didn't use the reticle for the KD AQT, but turned the dial the appropriate number of clicks I found at those other ranges.  I found that 9 clicks up gave me a good 400 yard zero, 6 clicks down was good for the 200, and 3 more clicks down for the 100.  I was in the 230's for the AQTs.  I back calculated the approximate bullet velocity for this ballistic pattern and it came in around 2850fps.

What's great about the bootcamp on days 3 and 4 is that you can really get to know your rifle.  The reticle for the ACOG will take some practice if you want to use it for your elevation adjustments as it was intended because it is in meters (and that 10% difference is significant at distance when the bullet is falling) and also it was calibrated for a bullet at 3250fps.  You can't get that velocity with a 14.5 inch barrel.  That's why I used the clicks at the bootcamp, and also  use the same aiming point.

Of interest, the TA11 ACOG (3.5x) has its reticle calibrated at about 2850fps, so may be a better choice for the shorter barreled ARs.  Its still in meters though, so using the 400 meter mark will probably put your group high. 

Offline Guntuckian

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Re: Zero for KD
« Reply #11 on: March 06, 2015, 06:44:10 PM »
The 25 meter sight adjustment mnemonic that I use to keep it easy to remember proper rotation directions for adjustment of elevation and windage on the front post and rear windage adjustments is:

UP RIGHT IS RIGHT.

That is, to move impact UP on the front post, you turn the front post RIGHT (clockwise).

And, to move the windage point of impact RIGHT you adjust the rear sight adjustment RIGHT (clockwise.)

This works for AR-15 iron sights, or 10-22 Tech Sights.

Yes, the mnemonic is not Politically Correct.  But, it prevents me from adjusting the sights backward!

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Offline mjkten

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Re: Zero for KD
« Reply #12 on: March 06, 2015, 11:48:41 PM »
 There is some excellent advice here, many thanks. I'll make sure the AR has a 25m zero before i go. I do have a 308 bolt gun I may bring just for the experience.