AR Optics Heights

[TonyAngel]

Hey guys, I'm just looking for some ideas and wanted to run what I've been thinking past ya'll to see what your thoughts were and maybe get a couple of ideas.

This is what I'm running and practicing with these days...https://photos.app.goo.gl/7XBGiHPzCryvWRhX7

The one on the left is a 10.5" 5.56 and the one on the right is a 9" .22. When you lay one on top of the other, the length of the braces are within half an inch or so of each other. The point being that other than the way the .22 barrel sits low in the receiver (I didn't think of this when I ordered a 9" barrel), both of these ARs are pretty much the same. I use the .22 to practice target acquisition and transitions because ammo is cheap and I use the 5.56 for everything from target acquisition to recoil control.

While reading some posts on line, I came across a post discussing having an optic 1.93" off of the rail. I did some investigating and found that there are some benefits to this. I ordered a Geissele 1.93 mount and starting working with it. I found this height to be much more comfortable. I don't get a crick in my neck on long days of shooting and I've found it to be faster.

Now my dilemma. The 1.93 has it's drawbacks. The greatest being that it won't co-witness with any open sights. So, as you saw in the pic, I came up with a solution. Instead of switching all mounts to 1.93, I just use standard co-witness mounts and put them on 1/2" risers. Now I'm back at 1.93 plus or minus a hair or two.

I like this solution because, well, it's cheap and it works. Circumstances have left me with two stock mounts for my Romeo4T, so I put one on my 4M. These mounts are rock solid and bullet proof. I have no desire for QD, so I'm good with them. With this setup, I can run all sorts of stuff using standard height mounts while getting the height that I want, plus I can now have back up open sights and co-witness them.

It's probably my OCD kicking in, but now I'm wondering if I have introduced a new and unneeded point of possible failure by using the riser instead of dedicated 1.93 mounts. I like this setup because it makes it easy to switch optics for which I already have standard mounts.

The upper is 7075, the mounts are 7075, but the riser is 6061. Anyone know of a rail length riser made of 7075?

Opinions?

 

[Demi-human]

Opinions?

They’re both just blocks of aluminum.
For a riser block, there is not a huge difference between the two metals.

6061 is more corrosion resistant. Both will survive an impact that will destroy your optic.


6061 Aluminum

• Known as the all-purpose aluminum grade, most commonly used aluminum alloy for CNC machined parts.
• Yield Strength of ~276 MPa (~40000 psi).
• Brinell hardness of 95.
• Elasticity of 68.9 GPa (10000 ksi).
• Melting point range of 582°-652°C (1080°-1205°F)

7075 Aluminum

• One of the strongest aluminum alloys with strengths comparable to many steels.
• Yield Strength of ~503 MPa (~73000 psi).
• Brinell hardness of 150.
• Elasticity of 71.7 GPa (10400 ksi).
• Melting point range of 5477°-635°C (890°-1175°F).

It seems like a difference, but not for the purpose you state.
If 33,000 Psi makes or breaks your rail, stop driving semi-trucks over it...

Use what you have without worry, saving you time searching and money spent for naught.

 

[taliv]

i recently started using 1.93 mounts on my ARs too. so far, i'm a fan. however

The 1.93 has it's drawbacks. The greatest being that it won't co-witness with any open sights.

that's not much of a drawback. i don't even put irons on my guns anymore. waste of time and rail space. the REAL drawback is the enormous hold overs required. 3" hold over is huge.

It's probably my OCD kicking in, but now I'm wondering if I have introduced a new and unneeded point of possible failure by using the riser instead of dedicated 1.93 mounts.

that's the way i'd characterize it. unnecessary point of failure. but i'd just get rid of the irons totally. problem solved! put your $ in good optics

 

[792mauser]

Melting point range of 5477°-635°C (890°-1175°F).

That's a heck of a melting range.

 

[Demi-human]

Melting point range of 5477°-635°C (890°-1175°F).

That's a heck of a melting range.

It’s because I cut and pasted, without proofing!
5477 C is 9890 Degrees Fahrenheit! That’s nearing partially ionized plasma temperatures!

And its because Aluminum is such a composite metal.
The composition of 7075 aluminum consists of the same alloys as 6061, but differs in the amounts of magnesium, silicon, iron, copper, zinc, titanium, manganese, and chromium, and additional trace elements.

Even in the 7075 group the ratios vary and cause the range of melting temperatures.

Just for fun...
The physical properties of A380 cast Aluminum.

• Tensile strength: 159 MPa (23,100 PSI)
• Fatigue strength: 138 MPa (20,000 PSI)
• Shear strength: 185 MPa (26,800 PSI)
• Hardness: 80 (Brinell Scale)

Composition (%, Range or Max)

• Aluminum: 80.3-89.5
• Copper: 3.0-4.0
• Iron: 1.3
• Magnesium: 0.1
• Manganese: 0.5
• Nickel: 0.5
• Silicon: 7.5-9.5
• Tin: 0.35
• Zinc: 3.0

Pros

• Extremely affordable
• Easy to manufacture

Cons

• Brittle, prone to cracking
• Potentially unsafe
• Difficult to anodize

For my clutzy ways, a cast receiver is not up to snuff.

 

[TonyAngel]

OK, it is my OCD kicking in. I tend to over think some things.

In any case, yes, I like the ~2" sight height. I find it to be super fast for me. It's like having one less step to do to get on target. I dropped about .1 of a second on my low ready and high ready drills on the first day and my neck felt a lot better at the end of the day.

I didn't go to any expense for back ups. I just thought it was a consideration. To be honest though, I don't think I REALLY need them. For the type of stuff that I might wind up having to use my AR for, Just having the tube of the red dot to look through is enough for anything close. Just having it to aim over really.

When I was shopping for a red dot, I shopped and shopped. My knee jerk was to grab an Aimpoint, but (and not trying to ruffle any feathers here) the Aimpoints are kind of behind the times in terms of what they offer, other than a red dot. And in my mind, their proven track record (proven through use) doesn't mean that there isn't something that can be just as reliable.

Anyway, after shopping around, I settled on a Sig Romeo4T. For those scoffing that it's a piece of made in China crap, I'm not sure about the China or crap part. After poking around, I found that the Romeo4T and its mount are made of 7075. It has an IPX8 water resistance rating. Sig uses steel thread inserts in the mounting screw holes and as it turns out, the mount it comes with is rock solid. When installing it on the rail, it feels just like my Geissele. The return to zero is amazing while using nothing more than a 1/2" open end wrench, which I keep in my grip. When I pulled the mount to try out the Geissele mount, it was labeled "Designed in Oregon, Assembled in the USA." Yeah, that's a little vague, but at least it doesn't say made in China.