Iron sight convergence: Different for different rifles (duh!)

[AZRedhawk44]

I've been shooting an M1A for awhile.  When not shooting an M1A (but still shooting centerfire), I tend to shoot my Mosin Nagant 91/30.

Ballistically, the 7.62 NATO and the 7.62x54R have a lot in common.  Similar velocities.  Similar bullet offerings.  I'll typically shoot a 165gr softpoint from the NATO round, and a 180gr surplus bullet from the x54R.  Given the increased diameter of the x54R's .311-ish bore, the extra weight doesn't do a lot ballistically for the rifle.

The M1A has amazing aperture sights on it.  The Mosin has bleh ladder sights on it, but they aren't too bad I guess.

What was most remarkable about shooting these two guns was the fact that a 25 meter AQT zero would correspond to a convergence later on downrange right around 250-275 yards.

So, I've got a new inexpensive AR-15 that I've put together in A2 configuration.  Got her sighted in for 25 meters.  Head out with Wayne to Ben Avery this morning and we shoot a few redcoats, AQT's, squares and such, then run some large targets out to the 200 yard backstop (as far as we can go on the general range).  This is only the second time I've shot this rifle

Line up the sights on it, 6 0'clock sight picture, squeeze... obviously can't see the .22 caliber hole down there even with binoculars, so I fire a group of 10.  Head down range and they are impacting above the torso-sized target, probably 10 inches or so higher than I wanted.

Dummy!  The sights are two or two and a half inches higher on this rifle than on the M1A or Mosin.  The bullet is also about 200fps faster.  With a 25 meter convergence that means I am pitching the thing upwards with a lot more loft, and the extra 200fps means it ain't coming down as fast.  Seems a 25 meter zero on an A2 configuration AR-15 is more equivalent with a 400 yard convergence.

Dialed down 5 minutes.  Life was good.  :-)  Thanks, Appleseed!

Moral of the story:  Know your rifle's trajectory and convergence point if sighted for a very close zero.  Find it out first-hand.  Were I to shoot at redcoats 200 yards away yesterday with this rifle, I would have been shooting over their heads very consistently and uselessly.

[wcmartin1]

OK, I'm a HP shooter and use a 6 o'clock hold.

With my AR my AQT zero is very close to my 300 yard zero (1/4 minute difference with my rifle/eyes.)

With my M14 my AQT zero is my 200 yard zero.

[AZRedhawk44]

Anyone else? 

Looking for a good ballpark to expect for convergence of a 25 meter zero.  I may have been over-estimating with a 400 yard convergence, but it seems like it's greater than 300 for my rifle if it's 10 inches high at 200 w/ a 25 meter zero.  Probably around 350 or so.

I need a piece of dirt that I can play with, out to 400 yards.   

[Fred]

   

Probably around 350 or so.

     AZ, you can figure it out fairly precisely.

     With your 25m zero, your rifle is 5 MOA high at 200.

      How many additional yards past 200 will it take the bullet to drop 5 MOA?

      Naturally, you verify calculated zeroes at actual distance at the first opportunity.

[AZRedhawk44]

How many additional yards past 200 will it take the bullet to drop 5 MOA?

That's the problem... I don't know.  It depends on velocity.  .22 rimfire will take about 25 yards past 200 to lose 5MOA.  .223?  I dunno.

The difference between a 55gr @ 3000 or a 69gr @ 2800 doesn't matter hugely, but I don't have a means by which to know how far a 60-ish grain projectile moving at about 2900fps will travel forwards while dropping 5 MOA.  Hence the request for anecdotal evidence until I can verify, someday, when I find a 400 yard range I can monopolize for this experiment.

I am saying I ran with assumptions I held that a 25meter zero generates an approximate 300 yard zero and found that I was 10 inches high at 200, and that bullet isn't going to drop 10 inches from 200 to 300 yards.  It will drop 6-8 inches in that distance, probably.

[Junior Birdman]

"Standard" (whatever THAT is) come ups for the AR15 (20"  bbl and M855 ball):

100-200     2 MOA
200-300     2 MOA
400-500     4 MOA
500-600     5 MOA
600-700     6 MOA
700-800     7 MOA

But I've seen them vary as much as a couple of minutes just because there are so many variations in the rifles and ammo. That's why you verify at known distance.     JB

[Fred]

    AZ, maybe you could move to someplace with wide-open spaces, and set up an improv range?

[AZRedhawk44]

    AZ, maybe you could move to someplace with wide-open spaces, and set up an improv range?

I've got places I can shoot to 300... but nothing further so far.  I dunno, maybe I need to go for a long, long hike back into the superstition mountains with my rifle, a couple hundred rounds and some targets.  Hard to set up a paper target without a stand though.

I know of open spaces > 300 where it's legal to shoot (no shooting across roads and the like), but they're not exactly truck-friendly.

[Nickle]

25 meter convergence for an A2 series AR shooting M855/SS109 equivalent ammo (62 gr) is 300 meters, plus 1 click.

To zero the AR, the US Army way, set your rear sight at 300 meters, plus 1 click, then zero at 25.

For an A1, zero at 25, using the small arpeture. You'll be on at 300. There is no elevation to A1 type sights, other than the front sight. Change your hold for the various ranges.

[Francis Marion]

AZ, here's the USMC method for sighting in a new A2. 
Nickle has already condensed this info into his post; see all written procedural details in pdf here:
http://appleseedinfo.org/smf/index.php?topic=2088.0