I hope I'm missing something obvious...

[mikbau]

Howdy all

It's been a super busy year, and I've not been able to spend any decent amount of time trying to sight in my irons until today. I'm having an issue that I can't sort out for the life of me.

My windage adjustment is cranked almost all the way to the left to hit dead center at 25 yds. I feel like I've triple checked everything: the sights appear to be mounted to the rails correctly. The rails on the upper and handguard seem to be aligned properly. The barrel appears to be straight and installed correctly. The sights don't appear to be bent, and from what I can tell, there doesn't seem to be any glaring issue in their manufacturing.

If you look at the rear sight from the top, it's really obvious the aperture of the sight is way off of the center line of the upper.

Troy Battle Sights
VLTOR upper
YHM Handguard
Daniel Defense Pencil Barrel

Anyone have any thoughts here? I really hope I'm missing something stupid and obvious. Otherwise I need to get it to a smith' to see what's what

thanks
Mike

[spamsammich]

Take a straight edge and make sure your rail is lined up straight with the upper, it could be canted. How many clicks left is your windage exactly from mechanical zero?

[mikbau]

I've tried the straight edge. It's REALLY close. I suppose it could be canted by a couple hundredths at the very most.

On the sight, there are 7 lines from mechanical zero to absolute left (0 being center, 7 being left) It's on line 6. I believe each line represents 4 clicks. It's literally almost all the way to the left.

[spamsammich]

it doesn't take many degrees to throw windage way off. There is a possibility that the tube twists along its length depending on how long it is. Are you sighting in with the small aperture?

[mikbau]

Yes, I am sighting in with the small aperture.

[Warg]

I had a this problem with a YHM rail. The first, and last, I ever purchased. The rail was aligned perfectly with the upper, but wasn't machined correctly, i.e., the top of the rail was very slightly torqued or twisted at the muzzle end. I was able to determine this by removing the sights and placing the upper on a very flat surface- upside down, of course. Now mine was minor and didn't quite require the amount of adjustment in the rear sight you've mentioned.

Edit- Probably shouldn't mention it, but you're sure the barrel nut is torqued correctly and fully seated in the upper? Jam nut too?

it doesn't take many degrees to throw windage way off. There is a possibility that the tube twists along its length depending on how long it is. Are you sighting in with the small aperture?

[Iraqgunz]

I don't know which YHM rail you have (I'll assume it is the one with the thick aluminum barrel nut and the the threaded rail that slips over it and is secured by the steel jam nut). We had those models on the BM carbines in Iraq. They were absolute shit and though we had a non-rail mounted front sight, I did configure a few just like that.

The rails were a pain in the ass to keep aligned and when guys mounted the slings on the their sometimes they would twist the rails. This was after I aligned and tightened them as best I could.

In short I would look at the rail first.

[mikbau]

Thanks guys

This is the model I have:
http://yhm.net/index.php?main_page=p...7b5af9678d97c0

it's the lightweight version, specter length.

By just looking at it, it doesn't look twisted - I haven't had a sling mounted to it yet. But, I guess the machining could be off on the top rail where the sight is mounted.

I triple checked that the barrel was seated and the barrel nut is torqued correctly, and the jam nut is solid. What I can say is that the issue isn't that the forearm isn't twisting out of alignment from the rail on the upper. I am going to have a smith take a look at it before I disassemble it, but I'll most likely try the flat surface trick to see if the machining is off

~m

[wetidlerjr]

Thanks guys
This is the model I have:
http://yhm.net/index.php?main_page=p...7b5af9678d97c0
it's the lightweight version, specter length.
By just looking at it, it doesn't look twisted - I haven't had a sling mounted to it yet. But, I guess the machining could be off on the top rail where the sight is mounted.
I triple checked that the barrel was seated and the barrel nut is torqued correctly, and the jam nut is solid. What I can say is that the issue isn't that the forearm isn't twisting out of alignment from the rail on the upper. I am going to have a smith take a look at it before I disassemble it, but I'll most likely try the flat surface trick to see if the machining is off
~m

Any updates ?

[mikbau]

I had a smith look at it last night. If you hold the rifle vertically and look sort of down the top rail of the handguard towards the upper, it's a little bit off. Maybe 1/64th" or so. I am a little leery that 1/64" off would make THAT big of a difference, but I guess we'll see.

My next challenge will be to try to line it up. This may be tough with the YHM parts, as the handguard has set screws that are indexed into the barrel nut at a given interval - so I can't just loosen the set screws and rotate it. What I can do is rotate the barrel nut a little bit (since it needs to be adjusted clockwise) but I need to verify that it won't punch the gas tube. I *think* there is enough room to try it. That, or I need to sort out a different barrel nut/handguard combo....

Edit....I believe it's not the barrel nut that it indexes in to, but rather the jam nut - if that's the case, I may be able to tighten the jam nut the 1/64" without too much issue and the set screws can stay where they are....