Serious Problem with DD Fixed Irons on BCM Rifle

[Patrick_B]

Do you have the tools to measure the height of the front post?

Sorry I missed this. Yes, I have a good set of digital calipers, so I’m sure I could get this done.

[AndyLate]

Is it possible the front sight is intended for a rail gas block, not a handguard rail? How different are the front and rear sight heights measured from the rail? Not post and aperture, the entire sight.

By the way, a 25 yard zero crosses the sight line again at 400 yards. The height of the sights over the bore makes an AR entirely different from an M1/M1 Carbine.

Andy

[Patrick_B]

Is it possible the front sight is intended for a rail gas block, not a handguard rail? How different are the front and rear sight heights measured from the rail? Not post and aperture, the entire sight.
Andy

I cannot presently give an answer either of those, but assume DD can regarding the front. Once I have the upper back in hand, I can measure and answer the latter.

[AndyLate]

If BCM can get it zero'ed at 25 with different sights, then I am sure DD will get the problem sorted. DD are great sights.

Andy

[OdinIII]

Just to clarify, are you trying to get point of aim to match point of impact at 25 yards? If so, that’s not typically how it is done.

[Wake27]

Just to clarify, are you trying to get point of aim to match point of impact at 25 yards? If so, that’s not typically how it is done.

...it is and has been by the Army for decades.

[OdinIII]

...it is and has been by the Army for decades.

Correct, but for most civilians it isn’t desirable to be ~6” off at 100 yards.

[1168]

Just to clarify, are you trying to get point of aim to match point of impact at 25 yards? If so, that’s not typically how it is done.

Literally everyday with M4s and M16s numbering on a scale that makes the entirety of this site look pathetic.

[sjc3081]

Not sure how that will work out if I’m this low at 25 with no adjustment left, but I’m willing to learn.



That’s interesting, and I will look around. I’ve come across a couple of early featured M1 Carbines with sight blades too tall, and had to deal with that. A whole lot would have to come off this one, so I will look into that. Perhaps DD will shed some light on this for me as well.

Thank you both...

You dont understand bullet trajectory. Shoot it a 100 and see your point of impact.

[AndyLate]

Not sure how that will work out if I’m this low at 25 with no adjustment left, but I’m willing to learn.

1.5" low at 25 yards is basically a 100 yard zero on an AR because of the sight height over bore. A 25 yard zero requires a pretty steep trajectory and the POI would cross the POA again at 400 yards.

All academic, I would be displeased if I had to bottom out the front sight to zero at 100 yards. Hopefully DD takes care of you.

Andy