How much eye relief is "enough" eye relief? (.308 AR, My First Rifle)


December 20, 2007, 10:45 PM
Hi, THR Folks!

First off, I assure you I searched threads and books and the web and the Practical Long Range Shooting links on these questions. Maybe it's that early dementia again. :rolleyes:

MY GOAL: To invest in one good quality scope setup for close range fun plinking and medium distance target plinking (i.e., 20 yards to 600 yards) with a DPMS LR-308AP4 (16" Barrel, Flash Hider, iron sights front and rear, 4140 Chrome-moly steel AP4 Contour barrel, 6 grooves, right-hand 1x10 twist).

PURCHASE: I settled on and received (but haven't opened) a nifty EOTech 552 Red Dot Holo (.308 Ballistic Reticle, 1x, AA).

QUESTION 1: I am interested in adding the ('s pricey) 3x EOTech Swing-Out Magnifier, to toggle 1x or 3x. However, the specs indicate it has only 1.65 inch Eye Relief. Is 1.65 inches enough eye relief for a .308 rifle recoil?

QUESTION 2: For low-power scopes that are line-of-sight directly in line with the Standard A2 Front Sight, will a 1x magnification show the image of the rifle's front iron sight and a 3x magnification show a "shadow" of the front iron sight? (For example, the "Leupold Mark 4 CQ/T Tactical Scope 1-3x 14mm Circle Dot Reticle Matte", which has a 2 inch to 2.8 inch eye, a little better relief than the EOTech Magnifier..and just one big part to mount and zero.)

QUESTION 3: If it's true that a "shadow" of the front iron sight is seen through a 3x magnification image, is it best to just get a collapsible front sight to get the iron sights completely outta the way of a 3x image? (...still more money, since I'll already a need collapsible rear sight to fit under the 3x magnifier)

CAVEAT: I know I need to get out and just shoot the thing more and figure all this out, but that's not possible just now.... :(

Thank you in advance for your patience and always excellent advice!

Toad #2 (...i discovered a prior Toad on THR.)

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December 20, 2007, 10:55 PM
Check for relief when firing from the sitting position.
This is the position where your face will be the furthest forward.

December 20, 2007, 10:59 PM
Thank you, W.E.G.,

But i guess that's kinda my problem. I'm trying to figure all this out BEFORE i spend money on any more hardware (and thus regret it later). :banghead:


December 20, 2007, 11:19 PM
3.5-4.5 inches is typical eye relief.

December 20, 2007, 11:54 PM
1.6 inches is likely too close and you will end up with a nice crescent shaped cut above your eye.

Most folks I know set up the EOTech to co-witness with the iron sights, then fold down the rear. The iron sights are only used when the battery dies.

December 21, 2007, 12:56 AM
I personally will not put anything on a rifle that doesn't have 3.5" of eye relief. The scope on my 30-06 has right around 3.75" and works fine.

wayne in boca
December 21, 2007, 07:23 AM
I have a rifle just like yours,and although it looks like an AR15,it recoils like an M14.You certainly do not want a short eye relief scope,or you'll be looking different real quick.When shooting an AR15,it is common for shooters to touch the charging handle with the tip of their nose to maintain a consistent sight picture/hold.Real bad idea on a .308 .Enjoy your new rifle,I love mine.

Zak Smith
December 21, 2007, 01:17 PM
2.4" of eye relief is fine for 308 on an AR-10. Most conventional scopes have at least 3" anyway.

The biggest problem with mounting a scope on an AR platform is moving the scope far enough forward so that a normal, good cheekweld and stock position doesn't put you too close. The LaRue SPR and EER mounts are the way to go.


December 22, 2007, 12:00 AM
Thanks for your help, Gang!

But...I'm still in a quandry....

While the EOTech 552 alone on a .308 presents no eye relief problem, adding the EOTech 3x magnifier behind it IS a problem at only 1.6 inches of relief.

Conversely...the Leupold Mark 4 CQ/T 1-3x 14mm has switchable magnification in one tidy package....but is it's 2.0 to 2.8 inch eye relief for sure adequate on a .308?

Harumph! :banghead:

December 28, 2007, 05:06 PM
Crescent Club initiation ceremony

December 28, 2007, 05:19 PM
1.6" is marginal. i wouldn't hesitate to shoot it personally, but i'm one of those guys that mashes my nose into the charging handle on an AR anyway. I'd keep the stock solid in your shoulder though, and wear eye protection always (like i do)

December 28, 2007, 05:30 PM
Crescent Club initiation ceremony

Somebody wasnt very good at instructing. Either they were ignorant or did it to be funny.

December 28, 2007, 05:44 PM
My EOTech 4X FTS magnifier has 1.65” of eye relief... I have not fired it yet.
I usually have a problem with short eye relief because I wear glasses - I prefer forward mounted scout optics and iron sights.
I'll will try this set up from the sitting position as suggested and post a report after I try it out.

Wes Janson
December 28, 2007, 06:20 PM
That video isn't showing incorrect eye relief, it's showing the result of giving a non-shooter a heavy-recoiling rifle and then providing zero instruction in the proper use thereof (although I'd be willing to wager that the rifle's owner probably doesn't know how to use it properly either). In other words, stupidity was the cause of that, not the equipment.

I've not shot the AR-10 platform all that much, but I don't recall it having all that much recoil, relatively speaking. On the other hand, I can't really recall ever having been bitten by a scope. On the gripping hand, I've always worn glasses, and I wonder if that doesn't give me a slight advantage when the eye relief becomes too short.

I would suspect that it might be shootable, but it definitely would be close.

December 28, 2007, 06:36 PM
I would not use a 'scope with only 1.65" of eye relief on anything with more recoil than a .223.

Consider - what if you sometime, for some reason, have to make a very hasty snap shot, perhaps at someting uphill from you, or perhaps you haven't shouldered the rifle exactly right? You WILL get your eyebrow smacked.

December 29, 2007, 12:05 AM

I feel bad for the young woman in that video. She probably has a scar because the "instructor" she trusted is a moron.

Meanwhile, thank you all for your advice....


December 29, 2007, 10:27 AM
I think that guy stood behind her on purpose so she would get hit, her head stopped against him. Im not even gonna say what i think of him. :cuss: :fire:

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