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9/22/2017 12:11:25 AM
Posted: 1/1/2006 9:28:36 AM EDT
I have the ARMS 40a2 rear flip up sight. It has two apertures, one large, one small. I have been using the large aperture for 50 yards. Here is my problem....

Re-zeroed the sight yesterday at 50 yards, shot a baseball sized group of about 20 rounds.

Moved target out to 100 yards and it's shooting a good 5-6 inches high? Hmm, shouldn't it be shooting low if anything? Or hell, should still be right on target considering how flat the trajectory is.

Checked my sights, notice that my front post is turned WAY up. It's so high it can wiggle pretty easily, like a bolt that is only being held in with one or two threads, that is how it feels. I don't think this is right because to lower my group at 100 yards I would have to unscrew it even more.

Also, when I look through the apatures I can see much more than just a verticle post, the part of the front post that is tapered as well as the base are visible in my sight picture, is this wrong? I thought you take the post and put it in the center of the apature and sqeeze the trigger, should I be able to see my entire FSB when I'm shooting?

Sorry for the number of questions this is just ticking me off, first military style irons I've ever used and it's becomming frustrating.
Link Posted: 1/1/2006 10:27:10 AM EDT
[Last Edit: 1/1/2006 10:37:44 AM EDT by chickrepelent]
They make a taller front sight post for ARMS-40's, Colt removeable carry handles, etc. Bushmaster and DPMS sell them.

After I zero at 50 yards, I fine tune it at 100, 150 and 200 meters until I get it close enough. I don't mind being an inch high here and a inch low there.

If you only have access to 50 and 100 yards you can still do some tweaking with your zero but I would get a taller front sight post first.

I don't know if your problem has anything to do with using the large apeture or not. I only use the small one.
Link Posted: 1/1/2006 11:41:48 AM EDT
[Last Edit: 1/1/2006 11:44:46 AM EDT by Dano523]
The two apertures are battle, and long range (reason for the nuber stamped on the smaller aperture).

Starting off with the battle sight, your zero should be 100 yards. Sighting in shorter than this means that you are forcing the sights to look more downward than needed, and when you aim the rifle out to 100 with the 50 yard zero, it's going to shoot high.

So, zero the rifle out for the 100 yards (allows you to use the rear elevation knob settings correctly), then if you need to shoot at a shorter distance of around 50 yards, click the elevation knob up to around the 400 yard mark to make the sights look the more downward plain needed for the correct front sight post hold.

Note: For a 100 yard zero, click the rear sight all the way down, then come back up three clicks and set the knob number to 1/3 via the set screw, and then adjust the front post to zero out the sights for the 100 using the large aperture.
Link Posted: 1/1/2006 7:25:09 PM EDT
This isn't a typical A2 sight. The rear sight only has 2 apertures for range, a long and a "battle" aparently. I would have thought a gun requiring a taller post would have come with it but I guess I'm wrong...

So, does this mean I MUST buy a front sight post before I can get it to zero at 100 yards (considering it's still shooting 5" high)?
Link Posted: 1/1/2006 8:24:19 PM EDT
[Last Edit: 1/1/2006 8:28:38 PM EDT by chickrepelent]
I guess you could try zeroing with the small apeture or aim low but I would get the new front sight.Taller front sight

Notice how it says this sight should be used with the ARMS 40.
Link Posted: 1/2/2006 12:31:57 AM EDT
Link Posted: 1/2/2006 9:54:40 AM EDT
Well now to complicate things I did some further research and it apears that the taller post is only needed if you do not have the F marked front sight base. My gun did come with this front sight base...

I think I'm going to totally rezero everything (crank post all the way flush, 100 yard zero, ect...) and see if I still have problems. My dot sight is on it's way so I don't think I'll be using the irons much after that but I want to have them in case I need them.

All this being said, if I zero at 100 yards, how high will I be at 50? I don't want it to be more than a few inches if possible...

So another question: If I already have an F marked FSB, why do I need the taller post?
Link Posted: 1/2/2006 2:08:41 PM EDT
At a 100 zero, your going to be few inches low at 50.

To correct, crank the rear sight up to around 3 or 4 to solve the problem (make the sights look more downward).
Link Posted: 1/2/2006 2:09:28 PM EDT
Link Posted: 1/2/2006 3:45:14 PM EDT
To clarify things...

The gun is a STAG M4 profile, the FSB has the 'F' mark (meaning for 'F'lat-top yes?), the rear sight does not have ANY elevation controls what so ever, it is a ARMS 40A2 style bui.

I can't crank any elevation out of the rear sight because it can only adjust windage.
Link Posted: 1/2/2006 7:57:22 PM EDT
[Last Edit: 1/2/2006 8:01:07 PM EDT by Tweak]
Link Posted: 1/3/2006 1:47:34 PM EDT
[Last Edit: 1/3/2006 1:48:00 PM EDT by Dangasaur]
The measurement of where your arrows are pointing (I'm assuming from the bottom of the upper to the "valley" of the picatinny rail) is 1 and 11/16 of an inch.

Is there anything else I should measure?
Link Posted: 1/3/2006 2:21:17 PM EDT
[Last Edit: 1/3/2006 2:25:51 PM EDT by Tweak]
Link Posted: 1/3/2006 3:27:38 PM EDT
I'll take it over to the neighbors house to see if I can get you some more measurements.

I was looking at the barrel with the handguards off and it could just be an illusion but my barrel looks slightly bent upward. I HIGHLY doubt this is the case but maybe that is my problem.
Link Posted: 1/3/2006 3:51:08 PM EDT
Link Posted: 1/3/2006 4:22:16 PM EDT
No luck on the neighbor. I re-measured the upper and my measurements are very close to what you have. I looked at the picture of the two FSBs you posted. My FSB is definately marked 'F' so is it normal for the shooter to have to raise up the front post as high as it is in your picture?
Link Posted: 1/3/2006 4:31:53 PM EDT
I looked down the bore and I think I might actually have a bent barrel. No matter how well I center the "rings" created by looking down the barrel, there is always somewhat of a shadow on the "top". That being said if I flip the upper upside down I see the shadow on the lower portion.

Does this sound like a bent barrel?
Link Posted: 1/3/2006 6:04:36 PM EDT
It's official, bent barrel. Had 2 other people look at it and compared it to another AR 15 upper. Definately bent...
Link Posted: 1/3/2006 6:18:28 PM EDT
Link Posted: 1/3/2006 7:18:56 PM EDT
Stag M4 profile upper on top of a Stag lower.

I'm not to worried about it, from what I've heard Stag is a good company who I doubt will have any problems standing behind something like this. It's pretty obvious that it was just a bent barrel from the time it was made. The packing material was fine, gun has no marks on it, gas tube is perfect. Probably just 1 in a 1000.
Link Posted: 1/3/2006 8:01:11 PM EDT
Link Posted: 1/28/2006 3:51:30 PM EDT
Dangasaur, sent you an I.M.
Having the same problem with my new Stag M4
Link Posted: 2/1/2006 3:38:19 PM EDT
I think a 50 yard zero will shoot high at 100. 50 and 200 are the same POI. So, the bullet is on the rise at 100 yds., and above the POI for a 200 yard placement.

Do I have this correct? I think I do.

Tack
Link Posted: 2/2/2006 4:26:44 AM EDT

Originally Posted By Tack:
I think a 50 yard zero will shoot high at 100. 50 and 200 are the same POI. So, the bullet is on the rise at 100 yds., and above the POI for a 200 yard placement.

Do I have this correct? I think I do.

Tack



Dead on on the idea, but the bullet never rises up from it's path, it's the down ward sight plain that intersects the bullet path at the two marks as the bullet is dropping to earth due to gravity.

Kind of like changing in the sights does not make the barrel shoot the bullet any different in regards to it POI, only zeroing is makes the sights look where the barrel is sending the bullets.
Link Posted: 2/2/2006 4:28:26 AM EDT
In regards to the barrel being bent, you really need to pull the barrel to confirm.

It could be that the upper was milled wrong, and the upper barrel socket is out of spec.
Link Posted: 2/3/2006 8:36:07 PM EDT
tacks right. this is a simple explanation.
www.bobtuley.com/external.htm
Link Posted: 2/4/2006 12:49:58 AM EDT

Originally Posted By infsqdldr:
tacks right. this is a simple explanation.
www.bobtuley.com/external.htm



From the point that the bullet leaves the barrel, gravity is pulling the bullet down, even if the shot is at an upward angle. Since gravity is a constant, then the bullet drop per flight time is a constant as well.

In regards to a bullet curve, it is nothing more than the constant drop of the bullet (time in flight), by the amount of distance the bullet travels in regards to speed (FPS). This means as the bullet slows down due to resistance (air), the drop will be greater, hence a more stepper shape curve downward.

I think this was covered a while back, but no bullet has aerodynamic lift capability, hence it never rises from the original bore line flight patch, but begins to drop from the pull of gravity once it leaves the muzzle (even shot at a upward angle).
Link Posted: 2/4/2006 1:43:10 AM EDT
the sightline is the straight line to the target, not the boreline. the bullet is not on the rise relative to the boreline, but is to the sightline.
Link Posted: 2/4/2006 11:50:27 AM EDT
Infsqdldr, no worries!!!

We are both talking about the same thing.

Myself, I just refer to the barrel bore line/bullet flight path as the constant, and the sights adjusted to look down to intersect the bullet path at any given point to make the POI and the POA the same point (sights being the variable). Even when the bullet is path arched upwards to compensate for the drop, gravity is still pulling the bullet down.

Where the variable comes into play with the bullet being under or over the sight plain is the height distance of the sights over the bore (and how the sights are adjusted), and this creates the two different Zero points (higher sight plain over bore will result in longer distances/ greater above or below between the two given zero points).

Referring to the sight plain as the constant, may lead people on to believe that changing the sights does in fact change the flight path of the bullet (bore flight path), and as long as we all agree that the changing the sights does not change the bullets flight path out of the barrel in any way, I think that we can let this one go.
Link Posted: 2/4/2006 2:31:36 PM EDT
roger that. sorry for the confusion. damn semantics. cheers.
Link Posted: 2/5/2006 9:07:56 AM EDT

Originally Posted By Dangasaur:
I have the ARMS 40a2 rear flip up sight. It has two apertures, one large, one small. I have been using the large aperture for 50 yards. Here is my problem....

Re-zeroed the sight yesterday at 50 yards, shot a baseball sized group of about 20 rounds.

Moved target out to 100 yards and it's shooting a good 5-6 inches high? Hmm, shouldn't it be shooting low if anything? Or hell, should still be right on target considering how flat the trajectory is.

Checked my sights, notice that my front post is turned WAY up. It's so high it can wiggle pretty easily, like a bolt that is only being held in with one or two threads, that is how it feels. I don't think this is right because to lower my group at 100 yards I would have to unscrew it even more.

Also, when I look through the apatures I can see much more than just a verticle post, the part of the front post that is tapered as well as the base are visible in my sight picture, is this wrong? I thought you take the post and put it in the center of the apature and sqeeze the trigger, should I be able to see my entire FSB when I'm shooting?

Sorry for the number of questions this is just ticking me off, first military style irons I've ever used and it's becomming frustrating.



First, with the ARMS 40 type buis you will need the taller front sight post.

More importantly, you should always set BZO (battle sight zero) using the small long range appeture. The larger "Battle" appeture is used at shorter ranges to pick up targets more quickly.
If you zero with the small app, your groups afterwards should be good with either appeture.


Good luck with the bent barrel though.

John
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