I read the FAQ section and have an additional question.  

My front sight base is canted slightly to the right (noticably when looking through the sights).

In the FAQ section, possible causes included barrel movement as the barrel nut is tightened.

My question is, whould barrel movement as the nut is tightened tend to cause the barrel (and sight base) to cant to the right or to the left (as viewed from the butt of the rifle)?

Just trying to narrow the possible cause for the "leaning base".  Any help greatly appreciated.

TIA

The barrel nut has right hand threads.

If a barrel vise was used, the front sight might end up on the right side.

If a receiver vise was used, the front sight might end up on the left side.

Personally, I think a lot of these barrel alignment problems are really caused by small errors in getting the barrel extension on correctly.  Think about it.  The barrel extension is only an inch in diameter and the front sight is 16" away.  A misalignment of the barrel extension will be magnified.

That being said, some of these errors can be corrected by rotating the barrel.  Some folk here promote the idea of laying the upper on the floor and whacking the front sight with a soft mallet in the direction it needs to go.  Armalite even had a technical note with essentially the same procedure on their web site.  I'm thinking it works by rotating the barrel in the barrel extension.  The fraction of a degree change is too small to change headspace.

The barrel extension is screwed onto the barrel then the alignment pin is pressed into it. Then the barrel is set in a fixture that indexes the alignment pin to the center of the front sight base.

There is no misalignment of the barrel extension. If anything is mounted wrong it is the front sight base.

"Whacking" the front sight base rotates the extension in the upper not the barrel in the extension. Given that the extension is screwed on in excess of 80 ft/lbs it would take a lot of whacking to move the barrel in the extension.

Do not put the upper on the floor while hitting the FSB. Rest the carry handle against your thigh and tap the front sight base firmly. Using any form of solid resistance on the upper can bend the barrel or crack the upper.

Thanks for the quick responses.  Exactly the info I was looking for.

I think I'll take a whack at fixing it.

One more related question: with the rear sight set at zero center windage, how many clicks in which direction do you have to move the rear sight to zero the weapon? Right now you are dealing with a cosmetic situation; but, the front sight tower may have to be tilted to zero the weapon. How and where does it shoot? That is the purpose of the front sight.

Steve6,

AOG has a good point. I assumed that your windage was off. Is it?

ArmyOrdGuy and Tweak,

Yes, the windage is nearly all the way to the right. It didn't hit the stop but it's close.  

In addition, the front sight base is clearly canted towards to the right (particularly noticable when viewed through the Reflex optic).

I wont have a chance to try moving the base until tommorow.  

Also, the manual I have indicates that the barrel nut assembly screws into the receiver assembly with 31-35 fp torque.

That doesn't seem like a lot so I'm thinking I will need to be carefull not to move the FSB too far.  I plan on using a rubber mallet and a light touch (initially).

If anyone's interested, I'll post tommorow with the results.

Thanks again.

I'm having this same problem, just not as bad with a Bushy barrel I just got. Marked to keep up with this thread.

MM419

The range for the barrel nut is 30-80 ft/lbs. If you are referring to oldguy's post, he (and I in my response to him) was talking about the barrel extension screwed onto the barrel, not the barrel nut screwed onto the upper receiver.

What make of gun are you using? Just for the files. [:)]

Tweak,

Sorry I didn't get my idea across.  

I wasn't disputing the torque value you gave for the barrel extension.  I was Refering to the torque of the barrel nut assembly to the upper receiver.  

31-35 fp torque didn't seem like a lot and as I understand it, the whack will cause the barrel nut assembly to turn in the receiver (please let me know if I have "assumed" here).  That's why I figured light taps would be best, at least initially.  

BTW, that 31-35 ft lb was for the torque wrench used in combination with the combination wrench.  I don't have the conversion formula handy so I don't know what the actual torque value for the receiver is.

Anyway, to answer your question it's a Colt M-4 new from the factory (or so I'm told).  

I fixed the FSB today.  I held the rifle across my thighs while seated as Tweak recommended.  This allowed for immediate feedback as to just how hard I was tapping the FSB.  When I reached the "charliehorse imminent" level of force, I moved the rifle closer to my hip.  A couple more whacks, slightly harder than before, and the FSB appears almost perfectly verticle.  The front sight post is still about 1/16 -1/32" slightly right of "perfect".

I was reluctant to use additional force to move the FSB the last fraction of an inch.  I'm going to the range tommorow and see how it shoots and go from there.

Minuteman419,

I didn't have to hit the FSB all that hard and the plastic faced hammer didn't even leave a scratch.  I did hit the FSB below the "ears".  Less leverage but I was afraid of bending or breaking it.

Thanks for all of the helpfull advise.

[img]http://pic2.picturetrail.com/VOL33/1216349/2303971/30579118.jpg[/img]

I was clarifying.



It's not, but it doesn't need to be given steel on aluuminum threads, the locking action the gas tube has, and the actual part the nut plays in holding the barrel.



You are turning the barrel in the upper receiver. Neither the nut or the extension should move.



Quite easily done too. Best to do this job on the range while zeroing, can save a lot of trips.

[ed for speeling]

Does whacking the FSB put any wear or undue stress on the parts (besides the FSB)?  Are there any dangers involved?  I've heard something like screwing up the locking lugs and M4 feed ramp line-up, is this true?  My FSB is canted to the right as well, but I'd rather wait and buy an Action Block and Barrel Wrench if there is absolutoley _ANYTHING_ wrong with whacking the FSB.

If your barrel is misaligned (windage maxed out) then the feedramps are misaligned. It does not matter if you align the barrel by whacking it or by loosening the barrel nut and reistalling the barrel. You WILL be changing the alignment of the extension in the upper.

If you insist on hitting the FSB too hard you can drive the alignment pin into the aluminum of the upper. If you have to drive the barrel over that far to align the sights then either the upper or the barrel is incorrect. If the barrel or upper is that incorrect you will have trouble lining up the gas tube and the bolt will probably rub on the barrel extension.

[speeling]

Currently I have to adjust my windage almost all the way to the right.  I don't know if the front sight base is installed wrong or if the barrel is off center.  I've taken the hand guards off and looked at it from every angle I can, but I still can't tell for sure what the problem is.  The M4 feedramps are lined up correctly in the barrel/upper already, I don't want to screw that up.  How can I tell if my barrel is indexed correctly without loosening it?  Where should I be looking?

At the rear sight aperture. If it's all the way to one side then your barrel is probably incorrectly installed.