Wednesday, July 18, 2018

Five Steps to Set Up Your Detachable Carry Handle AR-15 to Shoot Across the Course


Across the course highpower rifle competition is a challenging sport requiring consistency and precision.  The full distance course of fire consists an offhand and rapid sitting stage both at 200 yards, a rapid prone stage at 300 yards and a slow prone stage at 600 yards.

Marksman, sharpshooter and early expert class competitors typically shoot this course of fire with the same ammunition for all stages.  The most common of these is ammunition based on 77 grain boat tail hollow point bullets, the most common of which are the 77 gr. Sierra Match King, 77 gr Nosler Custom Competition.  Common competitions loads tend to approximate the ballistics of the U.S. military's Mk 262 Mod 0/1 ammunition used in designated marksman rifles.  Interestingly, this also approximates the ballistic path of US M118-LR 7.62x51mm sniper ammunition.  It's not an accident.  Standardization has many advantages for training and procurement for military systems.

77 gr ammo has the following ballistic drop characteristics when zeroed at 200 yards, the typical zero distance for a highpower rifle competition guns.

Distance (yards)Up (moa)Plus, moaClicks, 1/2 moaPlusClicks, 1/4 moaPlus
200 yd004060
300 yd2.5+2.510+516+10
600 yd13.5+1132+2260+44

Summary Video

Watch this video to get an overview of setting up the sight for a 200 yard zero.

 



Step-by-Step

Step 1 - Determine if you have a 1/2x1/2 or 1/4x1/4 rear sight



For service rifle competition using an AR-15 equipped with a detachable carry handle rear sight, setting the gun up properly is critical.  The reason is because the rear sight system only has around 18 minutes of angle (moa) of vertical travel from the bottom to top of its range.  This is around 36 clicks of movement range in a 1/2x1/2 moa rear sight and around 72 clicks of movement in a 1/4x1/4 moa rear sight.  Both still only give you 18 moa of total elevation.  This is critical to keep in mind.  This is not at all like the fixed carry handle M-16A2 pattern rifles that give much more vertical range of movement.

The rear sight assemble of a detachable carry handle only had 18 moa
or total verticaltravel; not a lot of room to waste.  It's important to make sure 
you have it set up so you can reach 600 yards from a 200 yards starting point 
with the ammunition you are using.  77 grain match ammunition behaves 
well with these sights.

Bottom out your rear sight and count the number of clicks to get to the top of the traverse range.  If closer to 36, you have a 1/2x1/2 rear.  Closer to 72 clicks and it is a 1/4x1/4 rear.

Step 2 - Set your rear sight to a standard 200 yard baseline point.

Here's the sweet spot.  These positions will give you sufficient movement range from a 200 yard zero to reach 600 yards with 77 grain ammunition.

For a 1/2x1/2 rear sight, come up 4 clicks from the bottom.
For a 1/4x1/4 rear sight come up 6 clicks from the bottom.


Front Sights



Now for the front sight basic math.  All M-16/AR-15 front sights use a common thread screw designed specifically  so that one full revolution of the front sight equals 5 moa of elevation movement in a 20" rifle length gas system service rifle barrel.  This is an utterly reliable constant.

A1-type five detent front sights adjust 1 moa per notch.  A2-type four petal front sights
move 1.25 moa per notch.  Both types change 5 moa of elevation per full revolution; that's
a function of pitch of the screw threads. 

For a detachable carry handle AR, it is critical that your front sight post be either a round pin A1 type front sight which has five cutouts, each cut equaling 1 moa of vertical change OR a four equal sided square blade front sight with four detent cutouts each equaling 1.25 moa of vertical change per cutout.  Remember, both equal 5 moa per full revolution.

Do not use the tapered front sights with a detachable carry handle gun. You can only move these in full rotations because of the tapered post and that will not work for the limited travel range of the carry handle's rear system.  Leave the tapered front posts for the fixed handle A2 guns.

Use round or square front sights for detachable carry handle guns; not tapered ones.


Step 3 - Rough Zero Your Rifle at 200 Yards Using Just the Front Sight

Now zero your rifle for elevation at 200 yards coming as close as you can by only changing the front sight post. Do save ammunition by making changes to your front sight boldly.  Remember that bullseye is good 6 moa in diameter.  Do a little math in our head or on a sheet of paper.

For example, let's say you have a 1/4x1/4 rear sighs and a previous zero with your rear sight at say 34 clicks up from the bottom at say 200 yards, it means your system is off by 7 moa.  That's 34 clicks minus 6 clicks pre-set up or 28 clicks divided by 4 because its a 1/4 minute sight.  So you need to turn the front sight so it is shorter, deeper into the hole, by 1 and 1/2 revolutions.  Then move the rear down to 6 clicks up from the bottom.  Fire a sighter shot or two, it'll be closer.

Another example, say you had a 1/2x1/2 rear instead with the same 34 clicks up at 200 yards zero.  You are almost at the top of the vertical travel limit of you rear. This clearly won't do.  The calculation here is that you want to get to 4 clicks up from the bottom of travel so 34 minus 4 equals 30 clicks divided by 2 because these are 1/2 moa sights.  So you are off by a hopping 15 moa.  Here you need to turn the front sight down, deeper into the tower, by three full revolutions then move the rear to 4 up from the bottom and fire the next sighter.

Step 4 - Refine Your Zero Using the Rear Sight

Once the front sight is really close as in within 1.25 moa from the center, make the final adjustment to the zero by dialing the rear sight no more than 1 moa of correction total..  If it's more than that, reset the rear to either 4 or 6 clicks up from bottom and make a front sight change by one detent up or down as appropriate.  Do this until you've got the shots going into the middle.

Step 5 - Record Your New Dope Card

Record the final number of clicks up from the bottom for your 200 yard zero then re-do your come ups dope card accordingly.  Remember to note both the absolute count from bottom given your final 200 yard zero baseline point in your card.  Mark it on the gun so it's easy to find.  Masking tape and a magic marker work well.

In a book or on the gun, keep your dope info handy.  Top gun is marked in MOA.
Botom gun has markings for sea level come ups as well as for a range at 2,600 ft elevation.
If you do this, you should be able to go across the course with your rifle with ease.

Variations

There is no one best way for setting up an AR-15 for across the course competition.  Here are a couple of more of them.

The 100-yard Method

The bottom line is that longer distance you can use to set up your zeros the better.  But if all you have regular access to is a 100-yard range, you can do this.  Bottom your rear sight and come up one click.  Then use the front sight to set up your elevation zero at 100 yards.  It'll be 2 to 2.5 moa up to 200 yards from this zero.  This will be more than enough to be on paper for sighters in an NRA match.  You get two sighters from position in NRA matches and you stay in position to fire your string.  It's a life of luxury compared to EIC shooting

I do not recommend relying on this or any single distance zeroing method for a CMP EIC match.  For EIC shooting, you need to confirm a hard no wind zero while in your actual firing position to account for cant and other head/body geometry variables, using the actual ammunition you will use at each stage of fire. There are no sighter shots when hunting leg points.  Every round counts.  Every point lost means no soup for you.

Advanced Shooting: The Perfect Eye Position Method

While this article concentrates on basics, there are some really cool advanced methods out there for shooting XTC.  Credit for describing this method to me goes to the very talented Sagen Maddelena, a former California Grizzly rifle team member who has gone on to become a truly spectacular Olympic caliber competitor.

Put your head on the stock and move the rear sight to where it looks perfectly aligned with your eye, kind of how you'd set up the rear sight of a match rifle.  Then set your front sight for a zero at 200 yards firing offhand so your natural head position is perfect.   Dial your normal adjustment for your cant, if any, for rapid sitting and also dial your normal come up on the rear for 300 yard rapid prone.  Here's the perfect eye trick.  For 600 yards, take your front sight tool and turn the front sight blade two or three full revolutions to take up 10 or 15 moa, your choice, then dial a final correction on the rear sight to get to you 600 yard dope.  This keeps the rear sight peep hole around the same height above the stock comb so it's perfect for your face and bone structure the entire match.

Yeah, that's innovative.  As another shooting champion friend Dennis DeMille once told me, at a certain point, your coaches can't teach you anymore, so it's up to you to discover the next level up the food chain on you own.

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