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View Full Version : Riser for Truglo red-dot on flat-top AR?


TheEngineer
08-24-2008, 8:04 AM
I've done a few searches but couldnt come up with much. I bought a Truglo red dot (TG8030B2) for my AR and a YHM (EOTech) riser. The dot doesn't co-witness with the front sight and is still ~1/4 to 3/8 low. Can anyone make a suggestion for this? I know I bought and EOTech riser for a Truglo sight but I had hoped that they both had the same HOB, evidently not. I've checked their website and they don't sell any mounts.

aplinker
08-24-2008, 4:23 PM
hmmm...

Do you know the centerline for your Truglo? (the optical center for the scope above the rail) How big is the diameter?

You'll probably need a good 1/2" or more rise. YHM makes budget picatinny risers.

maxicon
08-26-2008, 11:59 AM
Here's what you need to do.

The AR iron sights are at 1.4" centerline above the rail.

Measure from the base of the Truglo (where it sits on the rail, not the bottom of the clamps) to the center of the lens. It needs to be pretty accurate, but not super precise. Truglo lists that as a 39mm tube, so the height from the base to the bottom of the tube plus 20mm gives the same approximate thing.

Subtract that from 1.4", and that will give you the total riser height you'll need for absolute co-witness. Add 0.2-0.3" to get the total riser height for a lower 1/3 co-witness.

The YHM Eotech riser is only 0.3" tall, which is too short for much of anything except an Eotech. Since the Eotech already has absolute co-witness height built in, the YHM brings it up to lower 1/3.

There aren't that many risers taller than 0.6" or so. RRA's scout rail used to be 0.67" (but they redesigned it and don't have the spec listed, so you'd have to check), ARMS makes 3/4" risers (models 05 and 63), and Brownell's has a riser system that lets you vary the height:

http://www.brownells.com/aspx/ns/store/ProductDetail.aspx?p=23115&title=AR-15/M16/M4/CAR-15/AR-10%20MODULAR%20FLATTOP%20RISER%20MOUNT%20SYSTEM

http://www.armsmounts.com/catalog.php?action=124&item_id=2
http://www.armsmounts.com/catalog.php?action=124&item_id=85

http://www.rockriverarms.com/index.cfm?fuseaction=category.display&category_id=317


You can also get airsoft clones of the ARMS mounts if budget's an issue.

TheEngineer
08-27-2008, 8:06 AM
That is exactly what I needed to know. Brings back memories of the old adage about "ASSumption" my parents used to tell me... Thanks for the replies!