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Posted: 9/20/2004 10:54:17 PM EST
[Last Edit: 9/20/2004 10:56:04 PM EST by Sharkman629]
Last Saturday I was at Bill Goodman's Gun and Knife show looking for uppers for my M4gery. After going around the floor I noticed most dealers selling 14.5" bbl uppers with the wrong rear sights. Almost all of the receivers I looked at had the 8/3 zero on the rear sight instead of the 6/3. Isn't this the incorrect sight for an M4 sight radius? I have always been under the impression that and 14.5" bbl upper with M4 handguards sight radius required the 600/300 yard zero settings. All of the 14.5" and 16" bbl uppers with fixed carry handles had 8/3 rear sights. And only 5-7 of about 50 detachable carry handle uppers that I looked at had the 6/3 settings. For someone trying to build an M4gery as close as possible to mil-spec, this was a major issue for me. What say you?

Edited for typographical errors.
Link Posted: 9/20/2004 10:56:43 PM EST
A2 always has 8/3, detachable is supposed to always have NM or 6/3.
Link Posted: 9/20/2004 10:57:45 PM EST
Link Posted: 9/20/2004 11:06:17 PM EST
Link Posted: 9/20/2004 11:52:17 PM EST
[Last Edit: 9/20/2004 11:58:03 PM EST by Sharkman629]

Originally Posted By Tweak:
I'd be worried if they were using the wrong rear sight bases, the 6/3 is a carry handle thing not an M4 thing.



According to pages 0011 00-2 and 0011 00-7 of the following manuals it is:
Army TM 9-1005-319-10
Air Force TO. 11W3-5-5-41
Navy SW 370-BU-OPI-010

Operator's Manual For
Rifle, 5.56 MM, M16A2 W/E (1005-01-128-9936) (EIC:4GM)
Rifle, 5.56 MM, M16A3 (1005-01-357-5112)
Rifle 5.56 MM, M16A4 (1005-01-383-2872) (EIC:4F9)
Carbne, 5.56 MM M4 W/E (1005-01-231-0973) (EIC:4FJ)
Carbine, 5.56 MM M4A1 (1005-01-382-0953) (EIC:4GC)
Headquarters, Department of the Army
October 1998

From page 0011 00-2
25 Meter Zeroing Procedure (Cont)
Battlesight Zero
c.:

The 300-meter mark is aligned with the mark on the left side of the receiver. This will read 8/3 for the M16A2/M16A3 and 6/3 for the M4/M4A1/M16A4.


From page 0011 00-7
25 Meter Zeroing Procedure (Cont)
Battlesight Zeroing Adjustments (Cont)
3.:

Rotate elevation knob in the down direction (counter-clockwise). The elevation knob should stop on the 300-meter mark (8/3) M16A2/M16A3 rifles and (6/3) M16A4/M4/M4A1. The rear sight should be all the way down on the last whole "click" before it bottoms out. This is called mechanical zero elevation for the rear sight. If your range scale will not line up in the above manner, an armor will be required to adjust the range scale for you.


Edited to correct second quotation from manual.
Link Posted: 9/20/2004 11:56:09 PM EST
Sharkman, thats because the M16A2/M16A3 have an 8/3 carry handle and the M4/M4A1/M16A4 have a 6/3 detachable carry handle. The difference in zeroing procedure between the M16A4 and M4/M4A1 is to compensate for their different trajectories.
Link Posted: 9/20/2004 11:57:39 PM EST
[Last Edit: 9/20/2004 11:59:01 PM EST by Dave_A]
M4A3/M16A4 (detatchable handle)-> 6/3
M4/M4A1/M16A2 (fixed handle) -> 8/3
Link Posted: 9/21/2004 12:03:26 AM EST
By quoting the above manual, what I am trying to say is that I believe that all military M4 carbines, regardless of model, should have the 6/3 elevation settings due to the weapon's sight radius and velocity/trajectory differences with the 14.5" bbl.
Link Posted: 9/21/2004 12:08:52 AM EST

Originally Posted By Sharkman629:
By quoting the above manual, what I am trying to say is that I believe that all military M4 carbines, regardless of model, should have the 6/3 elevation settings due to the weapon's sight radius and velocity/trajectory differences with the 14.5" bbl.



All detachable handle guns should have it. Putting an 8/3 on a detachable handle will prevent it from being used on a rifle.
Link Posted: 9/21/2004 1:00:16 AM EST
[Last Edit: 9/21/2004 1:01:52 AM EST by Sharkman629]

Originally Posted By Combat_Jack:

All detachable handle guns should have it. Putting an 8/3 on a detachable handle will prevent it from being used on a rifle.



I guess what bothered me the most were dealers selling 14.5" bbl. "M4 uppers" that had fixed carry handles with the 8/3 sight. Also, most detachable carry handle 14.5" bbl. uppers at the show had the 8/3 sight as well. IMO, if your trying to build an M4gery as authentic as possible, you should insist on the 6/3 sight.

As I understand it, the 6/3 sight is necessary because of the differences in the bullet's trajectory coming out of a 14.5" bbl. as opposed to a standard 20" bbl for an effective zero procedure.

However, and please correct me if I'm wrong, the M16A4 has a 20" bbl. and a full sight radius. If so, why does the manual call for a 6/3 and not an 8/3; if sight radius and trajectory are the cause for the difference in zero settings? I don't understand why, if only because the handle is detachable, the zero settings are different. There has to be a better reason when many detachables have the 8/3 sight.

I look forward to your thoughts.

Edited for typographical errors.
Link Posted: 9/21/2004 1:08:17 AM EST
This whole argument is inane. Does anyone really use those numbers to dial in at distance? They are way off, and pretty useless for this purpose on ANY rifle. Learn your dope for your rifle and ammo and be done with it.
Link Posted: 9/21/2004 1:25:29 AM EST

Originally Posted By Adam_White:
This whole argument is inane. Does anyone really use those numbers to dial in at distance? They are way off, and pretty useless for this purpose on ANY rifle. Learn your dope for your rifle and ammo and be done with it.



The issue here is strictly for authenticity. If done correctly, those numbers do give a good reference.
I've put in a few hundred hours at the range and that comment was, as you put it, "pretty useless".
Link Posted: 9/21/2004 1:26:13 AM EST
Colt made very few M4s with A2 uppers, these uppers had the 8/3 elevation wheels. All new Colt M4s have detachable carry handles and 6/3 so that's why the TM is written that way saying M4s have 6/3. No reason to write a TM for a few 1000 rifles that you will never see.
Link Posted: 9/21/2004 1:30:42 AM EST

Originally Posted By Sharkman629:

Originally Posted By Adam_White:
This whole argument is inane. Does anyone really use those numbers to dial in at distance? They are way off, and pretty useless for this purpose on ANY rifle. Learn your dope for your rifle and ammo and be done with it.



The issue here is strictly for authenticity. If done correctly, those numbers do give a good reference.
I've put in a few hundred hours at the range and that comment was, as you put it, "pretty useless".



The question seemed to be one of compatibility with barrel length for accuracy - not authenticity. My point was that neither one will be much use numbers-wise.

However, I bow to your superior internet marksmanship skills .
Link Posted: 9/21/2004 1:40:38 AM EST

Originally Posted By Adam_White:
However, I bow to your superior internet marksmanship skills .



Again, no need to be a smartass when someone is seeking an opinion.
Link Posted: 9/21/2004 1:41:54 AM EST

Originally Posted By gotm4:
Colt made very few M4s with A2 uppers, these uppers had the 8/3 elevation wheels. All new Colt M4s have detachable carry handles and 6/3 so that's why the TM is written that way saying M4s have 6/3. No reason to write a TM for a few 1000 rifles that you will never see.


Thank You.
Link Posted: 9/21/2004 2:38:01 AM EST
Link Posted: 9/21/2004 4:44:10 AM EST
Guys
The reason for the the 8/3 markings on the A2 upper and the 6/3 on the detachable carry handle is that the rear sight lug is shorter with less threads for elavation to allow it to fit in the detachable carry handle ,if the detachable handle has the 8/3 marked elevation knob it is incorrect because the sight can only elevate to the 6 height anyway because of the shorter lug.
Link Posted: 9/21/2004 7:14:24 AM EST

Originally Posted By Sharkman629:

Originally Posted By Adam_White:
However, I bow to your superior internet marksmanship skills .



Again, no need to be a smartass when someone is seeking an opinion.



As others are also trying to point out, the difference has nothing to do with bullet trajectory, but everything to do with physical room to move the knob. Clearly, since the 14.5 inche barrel and 20" barrel use the same sights, the numbers can't be top precise - even if supposedly calibrated for a certain barrel length with a certain round. On top of that, most of us do not shoot the green tip GI ammo that it WOULD be calibrated for if it ever really was.

I may have come off as a smartass, but your comment of "hundreds" of hours brought that out of me. Many others here, including myself, have put far more than that both behind the trigger and pulling pit duty in just any one particular shooting season.

You asked for answers, and - between all the posts here - you have recieved them. They are:

1) The difference is based on whether the carry handle is removable or not, NOT the barrel length.

2) The numbers are of little practical use anyway.

3) I believe you will find that, on either M4s or M16s, that the rear sight moves the same amount per click on both, bullet trajectory be damned.
Link Posted: 9/21/2004 2:11:43 PM EST
[Last Edit: 9/21/2004 2:41:10 PM EST by Tweak]
Link Posted: 9/21/2004 3:00:20 PM EST
Where's Troy when you need him

The reason why a detatchable carry handle is 6/3 and a fixed carry handle is 8/3 isn't because a fixed carry handle can shoot longer than a detatchable carry handle. It's because of the design of the two.

A detatchable carry handle uses a shorter screw because the screw of a fixed carry handle would have to goe through the top of the receiver.

When Troy shows up he'll explain it better than I can
Link Posted: 9/21/2004 4:47:18 PM EST
just a thought my rock river a2 came with the 6/3 rear sight don't know why you would need more elevation
Link Posted: 9/21/2004 7:02:42 PM EST
Vinnie and alpha15 are correct. The threaded portion of an A2 rear sight base is too long to use on a detatchable carry handle - it will stick out the bottom. Rear sight bases for removable carry handles are thus made shorter to fit. Because these shorter bases cannot "come up" as far as the full length A2 rear sight base, the range is limited to 600 meters instead of 800. The top of the EL wheel (the marked part that is held on by the little allen screw) comes in two flavors - one is marked 8/3 with range markings (4 5 6 etc) for a 20" barrel, and one marked 6/3 with range markings (3 4 5) for carbines. Right?
Link Posted: 9/21/2004 7:19:09 PM EST
I could be wrong, but I believe that the thread pitch on the screw is different between the 6/3 and 8/3. This is why one full revolution raises the sight from 300-800m on the 8/3 and 300-600m on the 6/3. Otherwise though, if you go from 300 to 600 m. on both sights, the rear sight should move the same amount of distance up relative to the receiver.
Link Posted: 9/21/2004 7:41:21 PM EST
[Last Edit: 9/21/2004 7:54:46 PM EST by Tweak]
Link Posted: 9/21/2004 8:13:05 PM EST

Originally Posted By Sharkman629:
Last Saturday I was at Bill Goodman's Gun and Knife show looking for uppers for my M4gery. After going around the floor I noticed most dealers selling 14.5" bbl uppers with the wrong rear sights. Almost all of the receivers I looked at had the 8/3 zero on the rear sight instead of the 6/3. Isn't this the incorrect sight for an M4 sight radius? I have always been under the impression that and 14.5" bbl upper with M4 handguards sight radius required the 600/300 yard zero settings. All of the 14.5" and 16" bbl uppers with fixed carry handles had 8/3 rear sights. And only 5-7 of about 50 detachable carry handle uppers that I looked at had the 6/3 settings. For someone trying to build an M4gery as close as possible to mil-spec, this was a major issue for me. What say you?

Edited for typographical errors.



Yeah, I was at the gunshow and you asked me about the rear sights. I *thought* the 6/3 thing was a carry handle only deal, but I wasn't really sure so I didn't say anything.

Umm, on reading your post, I note that you state that you were under the impression that a 14.5" barreled upper with M4 handguards required the 6/3 rear sight drum. Does this mean I get in trouble for putting carbine handguards on a Bushy 14.5 W/permanently attached Phantom?

Now I guess we both know that 6/3 sights are only for detachable carry handles.

Cool

Link Posted: 9/22/2004 5:11:46 PM EST
Tweak:
I quoted your post because you said the 6/3 issue "wasn't an M4 thing." I should have remembered the M16A4 had the detachable handle. I looked it up and your right, the part numbers are identical.
Adam_White
Sorry we both got upset. My use of "a few hundred hours" was only express that I am, by no means a newbie on the range. I said that when I took offense at my issue being called "inane" and being told to learn my dope. I know the numbers aren't exact, but they do provide a decent reference for iron sights. My desire for them is authenticity alone and I wanted to know the reason behind the differnce, especially if was for a reason to compensate for ballistical differences between barrel lengths. No disrespect meant, just thought your response was a little strong.
123whisper: Did I also ask you about the feed ramps? Sorry, I asked a lot of people about the sights and can't remember which dealer you were. Were you in the back area of the show floor? If we talked about this site as well, I remember you.
To All: Thanks for all of your points as you guys, as always, have cleared my brain's doublefeed.
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