View Full Version : SIG M400 Straightness

Sweet Shooter
October 26, 2012, 11:59 PM
I took my M4 out today and sighted it in at 50 yards with irons. I had to drive in the front sight post down/in to get the group to come up on the target while leaving the rear sight bottomed out. With .223 ammo was able to shoot a couple of smallish groups with the A2 irons. And though I had no fails of any kind, it feels like the gun is needing a bit of break in... I've got 50 rounds through it now. My eyes aren't brilliant so with Irons I'm rolling with it. However... I did notice that the rear sight in the handle is over to the left a bit to get on center. On inspection it looks like the detachable handle is leaning ever so slightly to the shooter's right which is what is calling for this off center zero. Getting home I put bubble levels all over the action and confirmed that in fact the handle is leaning. Do we live with this or is there a fix to stand that handle upright more. I haven't tried taking it off the Picatinny rail yet. I don't want to put a scope on this and I love the retro A2 stuff... any thoughts?

October 27, 2012, 09:04 AM
Did you pull the handle off to see if it isn't straight or if it's actually an out of spec upper receiver?

If it's the carry handle/sight assembly itself, you can just replace it (although personally I'd see if Sig would replace it for you to save the $). If it's the receiver, then it will need to go back to Sig. Personally, I'd suspect the handle/sight more than the upper; bad receivers are kind of rare on ARs.

October 27, 2012, 09:40 AM
You might take the handle off and reinstall. There might be some junk or burr that is causing the problem. It certainly would not be the first time.

Like the poster above, the receiver being out of spec would be pretty far down on my list of the usual suspects.

See if there is a burr or buldup of any sort on the handle and the rail. . .better yet, mount the handle on another rail and see what happens.

If you have another AR style or a friend who has one, that might be the easiest and quickest way to find the problem.

Sweet Shooter
October 27, 2012, 05:26 PM
I did take the handle off and reinstall. It came back up in exactly the same place. The upper is absolutely perfect/square as is the front post. To get center at 100 yards I have the sight over to the left exactly one increment on the scale. It works okay and doesn't sound much but it causes non symmetrical reflections in the handle channel which is a little off-putting.

I shot a nice 1.5 inch group at 100 yards with Hornady 40 gr V-Max but it averages about 5 inches with cheaper stuff. I'm getting glasses next week for my slight astigmatism... maybe things will tighten up then.

What group sizes are you all shooting with the A2 irons?

I love this rifle.


Here are some photos... is this amount of offset to be expected?

October 27, 2012, 08:48 PM
That's normal with irons... I've seen dozens of m16s and M4s a few clicks off center.

One of my guns is like that...

October 27, 2012, 09:18 PM
Yeah, that offset is really not all that much. If it shoots accurately with just that windage, I'd just go with it.