Rifle Scopes Cantilever mounts for 1-4 optics on AR

[graewolf]

I am going to put a Burris XTR on my AR (as soon as it gets here from SWFA), and I was wondering why I see most of them mounted back toward the BUIS and cheek weld farther back on the stock - NOT nose-to-charging-handle like I have been used to for years. The eye relief on this scope is really long - around 4 inches and is there any reason not to mount it farther forward and still use NTCH weld I am used to?

The other reason I want to mount it farther forward is to use a NV monocular (Envis 703) behind it. The NV is currently on a QD mount directly in front of the rear BUIS. I've looked at alot of pictures of AR's with canitlever mounted scopes and I might recall one that wasnt right up against the rear BUIS. I'm talking about a 2+ inch gap btw BUIS and rear of the cantilever mount. Why dont I see this, and NTCH cheek weld with scopes?

 

[CSTactical]

Vortex, Leupold, Burris, and ADM. We stock a good amount of these type of mounts.

Mike @ CSTACTICAL

 

[graewolf]

It has a mount with it it, I am just asking why I dont see scopes like this with long eye reliefs mounted farther forward and the shooter utilizing the typcial AR15 NTCH cheek weld. (plus I want to keep my night vision mounted where it is - LOL)

Burris 1-4x24 Xtreme Tactical XTR 30mm Rifle Scope

This is what it'll go on......

 

[sawman556]

ADM Recon X

 

[graewolf]

I'd still need the rear obj of the scope another 2 inches or so forward - to fit in front of that NV and to put my nose on charging handle (considering a 4" eye relief).

With a NTCH cheek weld your eye seems like it would still be under 2" from the scope. If need be, I'll just mount the BUIS and the red dot on a 45 degree.

 

[Crosshair]

I'd still need the rear obj of the scope another 2 inches or so forward - to fit in front of that NV and to put my nose on charging handle (considering a 4" eye relief).

With a NTCH cheek weld your eye seems like it would still be under 2" from the scope. If need be, I'll just mount the BUIS and the red dot on a 45 degree.

The offset buis and dot would help free up the rear rail space. But, as you see in the pic above, you still don't have much room even with an extra forward mount like that adm.

Could you justify a monolithic upper? That would solve it. You could easily put the optic 4"+ past NTCH without issue. They are kind of pricey, but very versatile.

 

[graewolf]

I've rail room ahead of the upper receiver...it might end up partially on both the receiver and forend. I'll know more once it gets here in a few days.

I just got to looking to see what it would look like that far forward, and couldn't find a picture of one mounted like that. Got to thinking there might be a reason....but maybe not. LoL

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[sawman556]

I was worried it wouldn't be enough eye relief but it is. Maybe it's my big nose??? I could also bump the scope about a 1/4" forward. You could probably move the mount one notch forward without any ill effects as well. Not sure you'll find any better option unless you go monolithic.

 

[graewolf]

Yeah, I've just been speculating how it'll go, patiently waiting for it to arrive so i can see for sure. Just bored at work and figured I'd ask. ;-)

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[graewolf]

I was worried it wouldn't be enough eye relief but it is. Maybe it's my big nose??? I could also bump the scope about a 1/4" forward. You could probably move the mount one notch forward without any ill effects as well. Not sure you'll find any better option unless you go monolithic.

Well, it arrived and got it mounted last nite. My set up is less than pretty - but its very functional. ALTHOUGH, the scope mount bridges the gap btw the forend and upper rcvr. The rear of the mount is barely hanging onto the upper rcvr. It seems very solid but I'll have to watch it closely.

With NV off, and NTCH cheek weld I can turn the scope up to 4x with very very slight vignetting - but I can move my eye forward slightly and resolve it if I absolutely need 4x, otherwise its perfect up to about 3.75x. I still may take off the BUIS and move the GG&G QD NV mount and scope mount to the rear and push the scope forward in the mount and see if thats better.

 

[sawman556]

Not sure what kind of accuracy you are going for but that wouldn't work for me. My advice, install a PRI FF tube and top rail. You also might consider a SOPMOD or STR for a stock. Just trying to help.

 

[Crosshair]

Looks like a lot of nice and expensive components. I would advise against having the scope mounted in any way to the full floating forearm, though. If you can squeeze the end with your fingers and flex it, which they all do, you will almost certainly have a poi that floats around too. I would say that would be an awesome setup with a monolithic upper, and since you have some cash invested in a nice rifle, great scope and NV, it would be worth it to not have it questionably mounted. Monolithic! I'm just trying to help too.

 

[graewolf]

As you both were typing, curiosity got the better of me and I was mounting it farther back. I'll maybe put the BUIS on a 45deg later.

I like the VLTOR with top rail but it is not long enough overall. I'd like a longer rail (rifle length) than what I have on it now eventually...and I'm very fond of the YHM rails. Monolithic may very well be the way to go.

The mount is mostly on the upper rcvr and it'll have to do for now though. The front of the mount is now barely on the FF tube (as opposed to barely on the upper rcvr) and I think even if the FF tube flexed at the other end it wouldn't change POI terribly, if at all - this is a carbine anyway, I'm not looking for 1/4MOA out of it, +/- 1MOA will be fine.

As far as stocks go, I like the VLTOR E-mod and Magpul ACS stocks.

PS - thanks for all the "help" - I havent sunk enough into this already ;D

 

[Oleshep]

As you both were typing, curiosity got the better of me and I was mounting it farther back. I'll maybe put the BUIS on a 45deg later.

The mount is mostly on the upper rcvr and it'll have to do for now though. The front of the mount is now barely on the FF tube (as opposed to barely on the upper rcvr) and I think even if the FF tube flexed at the other end it wouldn't change POI terribly, if at all - this is a carbine anyway, I'm not looking for 1/4MOA out of it, +/- 1MOA will be fine.

In my case I found that mounting with the scope mount touching the forearm section of the rail leads to non-repeatability in the mount and the need for excessive windage to zero the scope.. YMMV...

 

[graewolf]

OK, so your suggestions got the better of me. I had previously sighted in the scope with it as I mentioned barely hanging onto the front free float tube. Once zero'd, the results were less than desirable. Maybe a 2" group @ 100m, give or take. SO....I took the NV and mount off and moved the scope back fully on the upper. Went out with my last 10rnds of Barnes 110gr VOR-TX factory ammo and I figured it would be close enough on paper and shot 5 rnds at 100m in a rest. I couldnt see any hits with the Burris at 4x. So, I got my spotting scope and really still didnt see the hits. I went downrange and found 3 hits ALL OVER the cardboard box, nowhere near POA, and couldnt find the other 2. One at least 8 inches high to the left, another 4-5 inches high right, and the third just grazed the edge of the box at 3o'clock to POA. W T F.

I then brought the gun to around 30m and shot across my ATV seat. Made a 5 shot group probably 2 inches. Something....is very wrong. Scope and base seem solid, action and barrel seem tight. Maybe my barrel just doesnt like this ammo (its an AR Stoner SS 16" 1:8 twist). Gonna load up some of my own and try again. Finally got my 300BO dies but unfortunately the only 30cal projos I have are 220gr and 190gr SMKs, 220gr Pro Hunters and 175gr Berger VLDs...some of which were meant for my 300WSM. So just gonna choose one of those and try something different, but basically starting from scratch.

Anyone have another suggestion to look at why its.....was going to say "grouping poorly" but that AIN'T the word for this!