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Posted: 10/30/2001 12:59:24 PM EDT
If I zero my A1 sights for the 50/200 santose method, where will the "L" marked peep hit?

Link Posted: 10/30/2001 1:23:16 PM EDT
I've not run the model for this, despite having a M16A1 upper receiver I shoot monthly zeroed at 50 yards. Let me see what time I have. Fairly simple to stick the data back in the model and see where it predicts.

Recall this IBZ was developed for the M4 Carbine and only coincidently works well on longer barrels.

-- Chuck
Link Posted: 10/30/2001 2:01:57 PM EDT
Ya know I've thought of testing it but never got around to it. With a 20" barrel you can bet the 'L' will be somewhere between 300M & 350M for a 20". For a carbine with A1 sights its anyone's guess.
Link Posted: 10/30/2001 2:05:58 PM EDT
I don't have immidiate acces to a 300+ yard range, so I would live to hear what the predictions are.

Forgot to mention, I have a 20in tube.

Thanks much,
Link Posted: 10/30/2001 4:04:41 PM EDT
OK, the model for a 20" M16A1, shooting full velocity M193 Ball such as Winchester Q3131A, predicts that a 50 YARD battlesight zero will peak about 2.3" out about 150 YARDS and will have a second cross over at 250 YARDS -- how's that for coincidence with the normal 250 METER zero for these rifles.

Flipping sight forward to L(ong range) the model shows the distant downrange cross over at 395 YARDS -- call it 400 YARDS. Bullet is about 10" high, though, out around 200 yards -- not real flat.

For the M16A1 we can call this a 50/250/400 IBSZ battlesight zero. At least for now. With almost all civil ranges measured in yards it should be easy to confirm.

Note the original M4 IBSZ is a 50YARD/200METER zero (mixed measurements) taking advantage of easily accessable civil 50 yard ranges, but preserves the numbers on the sight wheel for the most part. Since there are no range numbers on the M16A1 sight we've nothing to preserve.

With a 50 yard zero and M16A1 barrel the bullet is 1" high at 75 yards, and 1.7 at 100 yards. If you grid your targets and use binos you don't even have to walk down range.

-- Chuck
Link Posted: 10/30/2001 6:11:34 PM EDT
Could you repost this or let me in on a link?? Jeff
Link Posted: 10/30/2001 6:27:50 PM EDT
I thank you sir!

Link Posted: 10/31/2001 8:00:21 AM EDT
May I ask what procedure you used to figure the change in impact going to the 'L' sight?

That 395 yards is fairly close to the 375M expected zero of the 'L' sight using the standard M16A1 zeroing method (using the 'L' @ 25M).

To tell you the truth I didn't expecte the far zero to be so far out.
Link Posted: 10/31/2001 10:39:52 AM EDT
I ran the numbers for a 20" using M193 myself. I do get close to 250 for a far zero and something like 1" high at 200M (nothing I'd notice when shooting at that distance as you are takling .5 MOA). Interesting it is still a 2 MOA difference to set the sight to 300M (328yards), the round will hit something like less than an inch off. Our field tests were right on.

Link Posted: 10/31/2001 11:30:12 AM EDT
The procedure is on the Maryland AR15 Shooters Website. Forest probably has a macro to post it.

There was absolutely no interest by the board owner here in posting it, even though I sent him a copy when it was first developed. Maryland AR15 Shooters stepped up to the plate.

-- Chuck
Link Posted: 10/31/2001 11:41:31 AM EDT
Forest --

The model is at home. The rifle's M193 trajectory isn't an exact match for the M4's M855 but the difference is probably not one click of the front sight.

Rifle zeroed at 50 yards with M193 shoots a higher trajectory and the second cross over is 230 meters, not 220 meters. At these ranges, the bullet has lost a lot of velocity, so to get that extra 10 meters down range takes another half inch of intermediate trajectory.

The M16's apertures are about 3.7MOA different (on a rifle} from my references.

Cranking the 3.7MOA into the model produced the 360 meter long range cross over.

I'll rerun this again just to see what it looks like, having the software switch back and forth from meters to yards has produced some confusing data.

-- Chuck
Link Posted: 10/31/2001 12:57:53 PM EDT
Thanks for the info! Part of my differences in numbers my be in the velocity (I just realized I was using MV at 0 degF when I was running trajectory calculations at 70 degF) Whoops!. Also IIRC the MV is taken at 15 FEET? If its 15Yards that would give me a far zero of 250yards.

Assumed Altitude is 500' and a mid range humidity.

Link to Maryland AR-15 Shooters Site

Look under 'Zeroing Methods'.
Link Posted: 10/31/2001 1:01:31 PM EDT

Originally Posted By Chuck:
Forest --

The model is at home. The rifle's M193 trajectory isn't an exact match for the M4's M855 but the difference is probably not one click of the front sight.

That is what I've seen on the range. Though I don't have access to a long KD range (I'm limited to either 200M or a 100 yard range for Known Distance shooting).

I'll rerun this again just to see what it looks like, having the software switch back and forth from meters to yards has produced some confusing data.

As long as you are doing that could you run and see what the 'L' would be for a M4 with an A1 upper running M193? I don't use the A1 aperture anymore, but it would be a handy thing to know. - Thanks!
Link Posted: 10/31/2001 2:44:52 PM EDT
Part I:

Confirmed the model: the flip to L on a rifle will move the second, downrange cross over to just a hair under 400 yards.

Part II:

The same basic effect take place with the M16 sights as the M16A2 sights comparing rifle to carbine lengths. The shorter barrel makes the "flip" a larger MOA than the rifle and that compensates for the shorter barrel's muzzle velocity. The model shows 425 yards (vs 400), using 5.7MOa rather than 3.5MOA for the flip. Trajectory is quite steep a this range, the bullet drops almost 4" the last 25 yards.

On a carbine with M16 sights I'd look for a "same plane" flip and drill one out to 0-2 size of the M16A2 sight to use as a CQB rear sight.

-- Chuck
Link Posted: 10/31/2001 6:53:32 PM EDT
Thanks again for the info Chuck!

BTW the A.O. same plane has a large hole and small hole like the A2. There is a review of it at the Maryland AR15 Shooters Site (under Product Reviews:Optics & Sights).
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