New upper built, BUIS problems

[windyhill]

Hello guys, just sighted in my new upper and while it groups nicely, it is shooting about 8 inches low at 50 yards. I have the front sight post almost completely bottomed out. The upper and barrel are Bushy. The front sight is a YHM folding sight/gas block, the rear sight is a ARMS #40L-SP. I have compared the height of the sights to some on another AR and they look OK. Could I have over torqued the barrel and caused this? Thanks, John

[SapperRob]

If this a factory upper then call Bushy. Over-torquing the barrel can affect windage, but I'm not sure about the elevation. The usual suspects with elevation are using the wrong sights, (ie. using a gas block sight on the rail or vice versa) or an out of spec upper.

Where did you get the parts and who built the upper?

[C4IGrant]

Hello guys, just sighted in my new upper and while it groups nicely, it is shooting about 8 inches low at 50 yards. I have the front sight post almost completely bottomed out. The upper and barrel are Bushy. The front sight is a YHM folding sight/gas block, the rear sight is a ARMS #40L-SP. I have compared the height of the sights to some on another AR and they look OK. Could I have over torqued the barrel and caused this? Thanks, John

A taller front sight post will fix your issue.


C4

[Tom_Jones]

deleted

[C4IGrant]

Wouldn't a taller front sight post cause the point of impact to be even lower?

Yes it would. I guess I mis-read his post and thought he said that he ran out of elevation. When I read the words BM and ARMS zeroing issues my brain automatically goes into a standard reply. :D



C4

[markm]

Wow! There's so much aftermarketness going on there, it's hard to say.

The ARMS 40 I borrowed zeroed great with minimal adjustment on a flat top/F front sight base. I tend to think that ARMS knows where the rear app should be. :confused: