How To Mount An Optic On AR15 Without Fixed Front Sight Interference

Trijicon MRO on AR15 with a2 front sight

Does it bother you when the fixed front sight on your AR rifle gets in the way of your sight picture while aiming through a low mounted optic?

While this problem exists for AR rifles with the removable fixed front sight and standard A2 fixed front sights, there are ways around it to eliminate the front sight post optic interference and they apply to other rifle systems too.

Here are some quick fix:

  • Change To A Flip Up Front Sight - Just tuck it away! A flip up front sight is the easiest way to deal with front sight post interference when looking through an optic. You get the benefits of sight co-witness when needed, and just fold it up when not needed.

A free float rail system is required, please check out these rail handguards here

or check out our complete AR15 upper receivers guide

flip up front sight on ar handguard
  • Use Offset Sights - Mount an angled offset red dot on the top receiver. The shooter can simply tilt the rifle and aim without the A2 front sight getting in the way
trex arms offset leupold deltapoint pro mount
  • Raise Optic Height - Raise the optic height to clear the front sight post out of the way as much as possible using a 1/3rd co-witness mount or an riser mount.
Scalarworks MRO mount
  • Use Magnified Optic - When using a magnified rifle scope, the front sight post does fade away when magnification increases and it will not get in the way of the sight picture
vortex razor 1-10x lpvo at 1x engaging targets
  • Piggyback Red Dot Setup - This is similar to using an offset sight while the reflex sight is mounted on top of a magnified scope to raise the height, which is popular for Trijicon ACOG and other magnified scopes. However, this is not the most common setup and can be expensive.
ACOG 3.5X SDP with RMR

Hope that helps!

Do You Need Co-Witness Sight Setup?

Sight Picture co-witness

Referenced LaRue Tactical

Why Is Co-Witness Useful ? - Co-Witness between the optic reticle and the front sight post gives the shooter the following benefits:

  • Use as backup sighting system in the event of optic failure
  • Use front sight post as the offset aiming reference point
  • Serves as a reference point for zeroing reflex & holographic sights (Only if iron sights are already zeroed)

When is it not neccessary? - Co-witnessing the front sight can be annoying for the following reasons:

  • Front sight post is generally bigger than a 2 or 1 MOA size reflex sight reticle that blocks the bottom half of the sight picture, and sometimes obscures overall field of view for target ID during day and night.
  • As optic durability and reliability have significantly improved in the recent years, the need for back up iron is almost rare unless optic battery dies

When To Use Absolute Co-Witness?

Absolute Co-Witness optic mounts are the least popular on AR15 rifles because it doesn't allow proper cheek weld for most people and it sits the optic way too low on the rifle.

A absolute co-witness height only works if the top receiver already sits as high as a 1/3rd co-witness and the cheek weld position is perfect like AKs and

When To Use 1/3rd Or Taller Co-Witness Optic Mount?

night vision goggle with ar15

Referenced The Firearm Blog

Better Clearance For NV Goggles -This also aids anyone who wears bulky safety glasses and a pair of night vision goggles.

Better Reticle Clearance - Having the reticle sitting above the front sight post provides a clean field of view that isn't obstructing the sight picture for zeroing and target assessment down range.

Ying Xu

US Air Force veteran nuclear weapon officer. Aerospace engineering bachelor's degree from the University of Kansas. Experienced as a certified NRA range safety officer. Working as a search engine expert for