A2 NM Sight Calculation

[D.B. Cooper]

I'm trying to set up a DOPE card for Service Rifle. NM A2 rear sight. 1 click = 1/2"@ 100 yrds (1/2 MOA) NM A2 front sight...I don't know what the adjustment is. (And that's my problem.)

55 grn zeroed at 100 yrds my rear sight is all the way down, bottomed out. No more adjustment. POI is 3" high. I need to raise my front sight post to bring that down to zero @ 100 yrds.

Does anyone know how many inches or MOA the POI will shift with each click (should be 1/4 revolution around the front post, IIRC) of the front sight post?

 

[CapnMac]

I have this fuzzy recollection that the "stock" adjustment was 1/2" and the NM was 1/4"--but that is relying upon possibly fickle memory, and not facts certain.

 

[shoobe01]

Depends on what exactly your components are. There is no NM standard so rears can be 1/2 - 1/2 MOA, or 1/4 - 1/4 MOA or... mixed! A popular thing for quicker windage adjustments on the firing line was to swap bits, get 1/4 elevation, 1/2 windage! I wouldn't be surprised if someone did that from the factory.

So either try to find all the paperwork it came with, or ask the manufacturer (if it's all totally stock) and see if they can tell for sure for your S/N (or they pinky swear they always do it one way), or ... we need a real expert and maybe your sight taken apart to tell.

Or, try it and see how far it moves with each adjustment?

 

[D.B. Cooper]

Or, try it and see how far it moves with each adjustment?

That's what I'm going to have to do. I just ran out of time at the range yesterday and have a match Friday. But the front matching the rear is logical.

 

[Laphroaig]

NRA blog says 1.25 MOA per 1/4 turn.

https://www.nrablog.com/articles/2016/7/americas-rifle-zeroing-your-ar-15/

I saw that on another site also.

 

[WrongHanded]

You could calculate the amount of adjustment you need, measure the front sight where it is, and turn it up to the difference.

 

[GooseGestapo]

On my RRA NM AR15 with 1/2 MOA adjustments, a 200yd -0- requires 4 clicks up for 300, and 20 clicks up for 600. That’s with a 75gr Hornady @ 2,750fps. Ditto an 80gr Sierra MatchKing over same powder charge. At 200-300, it’s also on for a 55gr at 3,100fps. Takes about +24 at 600yds. But I only tried it once...

At 100yds, they are still +3” which puts them center on a 100yd reduced SR1 (200yd) target.
I’d say you’re ready to go. A CMP and NRA high power match allows 2-sighter shots.
I’ve jut got 2 white lines on my elevation drum . 200/600 and 300. Easy to tell which is which.

 

[D.B. Cooper]

On my RRA NM AR15 with 1/2 MOA adjustments, a 200yd -0- requires 4 clicks up for 300, and 20 clicks up for 600. That’s with a 75gr Hornady @ 2,750fps. Ditto an 80gr Sierra MatchKing over same powder charge. At 200-300, it’s also on for a 55gr at 3,100fps. Takes about +24 at 600yds. But I only tried it once...

At 100yds, they are still +3” which puts them center on a 100yd reduced SR1 (200yd) target.
I’d say you’re ready to go. A CMP and NRA high power match allows 2-sighter shots.
I’ve jut got 2 white lines on my elevation drum . 200/600 and 300. Easy to tell which is which.

So...+3 @ 100 is 0 at 200, and add 4 for 300? And one complete revolution of the rear from 300 to 600? That kind of matches the ballistics calculator app, which says 7.5" of drop from 200-300 (55 grn bullet) which would be 5 clicks at 300.

 

[GooseGestapo]

Understand that I using a 6o’clock hold on the bull. The arc for the AR with milspec sights generates a 275yd zero (center) so, mid range rise puts them in the center of the respective targets.
The 200yd bull is 13” (12moa). The 300yd bull is 36”. The 600yd bull is 60”.

The 1moa M1 Garand battle sight is +2clicks from “0”, typically 10clicks up from bottomed out. +2clicks for 300yds, plus 10-11clicks for 600.
Depending on whether you’re using M1 or M2 ball/equivalent.

Yes, pretty close.
I refer to my log book I started when I bought the rifle. I only shoot it at CMP Talladega. Elevation is 550’msl if I remember correctly.

I have my front sight set +4clicks from bottoming out. This allows me to adjust to 100ys if I need to. Lately, I’ve been using a Nikon 3x AR Scope with target turrets. Scopes (4.5x max) are now allowed in CMP competition. I don’t have my scope dope established yet.

Due to arthritis, my competition days are over. That, and having to take a prohibited beta blocker for a heart arrithmia.

I prefer my regular A2, a DPMS lower with a PSA upper with a FN A2 barrel w7” twist. It’s perhaps 1moa with a 75gr Hornady bthp (1/2 price of VLD or ELD bullets -~15cents each), weighs 7.7lds and I can handle it off hand.
The arthritis is robbing me of my strength and muscle tone.

The RRA NM is 11.5lbs w/o 3.5lb butt weight and 1.5lb fore end weights. It’s a beast at 600yds with a 80gr Sierra MatchKing @2.555”OAL over 22.8gr of H4895. With the 1/2moa rear windage drum, I can pick which side of the X-ring it hits, it shoots under 1/2moa no-wind. So I’m either 1/2 left, or right. Wind is seldom more than 2clicks at 600 at Talladega. Nothing like the old Camp Perry range.
I need a 1/4moa windage drum to center it.