Warning

 

Close

Confirm Action

Are you sure you wish to do this?

Confirm Cancel
Member Login
Site Notices
Posted: 9/5/2010 11:12:37 AM EDT
[Last Edit: 9/5/2010 11:13:30 AM EDT by belliott]
Hello, sorry for the redundant post. There are a lot of threads out there on this site and others about this topic, but couldn't find any really recent threads on here about it.

I have a Texas Bushmaster M4A3 (DPS model) that I aquired in trade for a long range rifle I had. After about two weeks of owning and shooting it I just noticed that my FSB is ever so slightly canted to the right. I only noticed after I mounted an optic. I tried the table test (balancing it on the sights on a level surface) and it confirmed that it is off slightly.

When on zero my rear apeture is 1-1/2 lines off mechanical zero to the right. So its not like it's way off. Just barely enough to notice when i am trying to notice it. It took me two weeks to notice it in the first place.

What are the easy solutions? I keep trying to tell myself that it is no big deal. I mean I got a good zero, and the rifle hits good groups and has zero function issues. It just annoys me knowing it is not perfect.

Bushmaster CS told me that probably the FSB is not canted, but the barrel needs be re-indexed. Maybe, but I don't think so.

Please share your experiences and opinions on this.

Oh Yeah.....I want to fix it without sending it in. I am not the original purchaser and would have to pay shipping and for the repair anyway.

Thanks
Link Posted: 9/5/2010 11:14:46 AM EDT
Thats well within normal range
Link Posted: 9/5/2010 11:16:02 AM EDT
Originally Posted By JedYonkers:
Thats well within normal range


I agree.
Link Posted: 9/5/2010 11:20:00 AM EDT
I wouldn't worry about it, that's well within spec.
Link Posted: 9/5/2010 11:31:51 AM EDT
Thats well within the spec of 10 clicks , I believe anything more than that is a problem.I have a bushmaster barrel well it wasnt canted but was as you describe when laying it on its top..one ear could be lower than the other..finishing issue.Sounds like the rifle zeroed in 5 clicks.
Link Posted: 9/5/2010 12:37:26 PM EDT
I wouldn't worry about that small amount of clicks.
Link Posted: 9/5/2010 1:37:30 PM EDT
It takes proper tools and time to get sights perfect. I can get an upper within 1 MOA with the rear sight centered. Both the receiver and the barrel must be clamped when torquing the barrel and only after the rifle has been bore sighted with sights centered. The barrel is twisted to correct for windage, then the barrel and receiver are clamped and the barrel nut torqued to index the gas tube.
Link Posted: 9/5/2010 2:38:35 PM EDT
Or you can do what a Vietnam era Marine armorer showed me..us a small cut rectangualr piece of beer or soda can aluminum and put it behind the index pin wich bends and conforms to the index pin shape as the barrel goes into the upper..nice and snug and perfectlt centered and you get a barrel done in 15 minutes.If there is no play at all in the uppers slot when the barrel goes in its usually GTG.
Link Posted: 9/5/2010 3:54:47 PM EDT
[Last Edit: 9/5/2010 4:14:54 PM EDT by belliott]
I double checked how many clicks off it was from center just now....I clicked the rear sight back to perfect center from where I zeroed it at and it was 19 clicks.

I saw a post that the spec is 10 clicks. It still has plenty of room to move to the right (photo below), but do you think this is still too much off? I want to not worry about it, but being a perfectionist as many of us here probably are, it's annoying. Part of me says since it shoots fine to just let it be. But the other part wants it to be closer to center.

In these cases is it more common that the FSB is not installed correctly, or the barrel not indexed correctly? I have read that the pins can be bent that hold the FSB and can be replaced, but i don't know much about assembly and disassembly of the FSB.







Link Posted: 9/5/2010 4:06:49 PM EDT
People like us just don't like little misalignments like this, but in reality one or two marks off center is damn good. One thing that is never mentioned is shimming the carry handle, but there's only a small amount of shifting possible. This doesn't really correct the alignment but makes it less irritating . You mentioned mounting an optic - along with the carry handle? How does that work?
Link Posted: 9/5/2010 4:34:31 PM EDT
[Last Edit: 9/5/2010 4:40:15 PM EDT by belliott]
Originally Posted By 1saxman:
People like us just don't like little misalignments like this, but in reality one or two marks off center is damn good. One thing that is never mentioned is shimming the carry handle, but there's only a small amount of shifting possible. This doesn't really correct the alignment but makes it less irritating . You mentioned mounting an optic - along with the carry handle? How does that work?


It is mounted on my front quad rail and serves as a co-witness to my irons. Have to look down the carry handle to see the optic, but helps with quick aquisition.

Basically this is just temporary until I can afford the Micro T-1 and a good BUIS.

Thanks for your input. I am sure it is fine. I will try not to worry about it so much.
Link Posted: 9/5/2010 4:39:47 PM EDT
The armorer I learned from said 12 clicks but when I contacted Colt some time ago they told me 10.
Link Posted: 9/5/2010 4:41:22 PM EDT
Originally Posted By ChromeLined:
The armorer I learned from said 12 clicks but when I contacted Colt some time ago they told me 10.


So does that mean that 19 is way too much? It doesn't look THAT far off center, but it is definitely not inside 10 (or 12) clicks.
Link Posted: 9/5/2010 4:52:10 PM EDT
Originally Posted By ChromeLined:
Or you can do what a Vietnam era Marine armorer showed me..us a small cut rectangualr piece of beer or soda can aluminum and put it behind the index pin wich bends and conforms to the index pin shape as the barrel goes into the upper..nice and snug and perfectlt centered and you get a barrel done in 15 minutes.If there is no play at all in the uppers slot when the barrel goes in its usually GTG.


This is the best way to do it. If you want it to be even more exact, do what I did which is to zero your red dot at the range first at 100 yards, and then shim the FSB index pin as per the above method, however, instead of using a piece of beer or soda can, get youself a set of feeler gauges. These are basically a stack of gauges all with different thickness - see here:

http://www.google.com/products/catalog?hl=en&q=feeler+gauge+set&cid=14131781534791252310&ei=FjqETObeNoiSNrjjhL0G&sa=title&ved=0CAcQ8wIwADgA#p

you basically put different ones in until your FSB cant is superimpose on top of the red dot. Cut a small piece of that gauge off and put it behind the index pin with a drop of blue Locktite and put it all together- you are done!
Link Posted: 9/5/2010 4:53:22 PM EDT

Originally Posted By belliott:
I double checked how many clicks off it was from center just now....I clicked the rear sight back to perfect center from where I zeroed it at and it was 19 clicks.

I saw a post that the spec is 10 clicks. It still has plenty of room to move to the right (photo below), but do you think this is still too much off? I want to not worry about it, but being a perfectionist as many of us here probably are, it's annoying. Part of me says since it shoots fine to just let it be. But the other part wants it to be closer to center.

In these cases is it more common that the FSB is not installed correctly, or the barrel not indexed correctly? I have read that the pins can be bent that hold the FSB and can be replaced, but i don't know much about assembly and disassembly of the FSB.

http://i923.photobucket.com/albums/ad78/KimberElliott/september52010020.jpg


You will not bend the taper pins as they are hardened steel. More likely to damage the FSB. Shimming the index pin slot in the upper is viable but it won't fully compensate for assembly torque. Still the best bet is double clamping the upper and barrel after adjusting the barrel to bore sight with the rear sight centered. It works, the last two I have done this way have been within a single MOA from center.


Link Posted: 9/6/2010 7:55:09 AM EDT
How many clicks for an Daniel Defense A1.5 sight?

It has the same adjustment as an A1 rear sight.

I had to adjust mine 3 clicks to the left, It that the same as 10 clicks on an A2 sight?

It this in spec?

Thank You,

rfenergy
Link Posted: 9/6/2010 10:32:04 AM EDT
bump for info...
Top Top