Do I need a rail with built in MOA?

[wethington123]

It’s not just low-end optics. Short, compact, high-magnification scope designs tend to struggle with this more than others, IME. The Bushnell DMRII 3.5-21x was one of the worst I’ve seen.

Good to know! Haven't heard that, thanks.

 

[JDMBEND]

What is the downside to a 20 moa rail?

 

[Fred@Exterra]

Personally, I prefer rails that have mil elevation, instead of MOA. But that’s just me.

I definitely use a Mil rail with my FFP fixed power scope. Bomb proof combo.


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[Dave Thomas]

I didn't know that was an option, that shows how much I've looked into this. My scope is in mil, so going this route would only make sense.

It's a joke just like a metric crescent wrench.

 

[fuzzymarindave]

I'm in the middle of a rifle build, Rem 700 in 280AI. I plan to shoot 180 ELDm @2800, hopefully. I currently have a Nightforce 4-14x50 that I plan on using. I now need a mounting system, but I'm unsure what to go with.
My plan is to shoot out to 1000.

My experiences: I took two rifles to a long range course and both had 0 MOA rings mounted directly to the receiver. Both scopes allowed me to get to 1000 yards easy. The Leupold VX-6HD ZL3 almost got to 1-mile with dialing but came up a little short and I had to use the hash marks on reticle to hold over. The Leupold VX-6HD ZL2 did not have enough travel to get much past 1000 yards.

 

[coyotekilla]

So I plugged in a 280ai into the hornady app... 180 eldx I think @ 2600 fps. Maybe your barrel will be shorter, maybe the barrel will be slow. Basic calculations say 30 moa.

Id go with a 20 moa rail cause there really isn't a downside. Plus if you want to stretch it farther your good to go.

 

[Jordan Smith]

Good to know! Haven't heard that, thanks.

The DMRII Pro is a bit better with its improved glass coatings, but it still struggles when the erector gets much more than 5-10 mrad from mechanical center. At the extremes of the erector travel, the DMRII (non-Pro) is like looking through a fish bowl - darn near unusable if there is any mirage at all. The Pro is decent and usable, but not great.

FYI, I've owned and used 5-6 of each with the same results, so it wasn't just a single bad sample.

"Cheap" scopes aside, I've seen this behaviour in other mid-to-high-grade compact, high-mag scope designs, as well, but the DMRII is one of the worst I've used.

 

[Brandon_SPC]

I would try it without it first. My 6mm ARC doesn't have one and I am able to reach out to about 800 yards without one and that's shooting 108 eldms at 2550 fps around sea level with my Leupold Mark 4HD 2.5-10.

 

[Fred@Exterra]

What is the downside to a 20 moa rail?

There really isn’t a downside for the consumer, but it adds a layer of complexity for the manufacturer. If the scope and the bore are parallel, the crosshairs will always be below the optical center of the scope beyond 100 yards, the further you shoot, the more pronounced this is. Theoretically, the scope is clearest at the optical center (not such a huge issue on higher quality scopes). Additionally, windage adjustments can get squirrelly at the furthest extents of the elevation travel (not such a huge factor with modern scopes). Using a 20moa base keeps your adjustments above optical center for the first (approximately) 700 yards & below optical center beyond that… closer to center throughout its effective range.

On systems with very slow moving projectile, we design this offset directly into the weapon so the scope is optically centered at the median distance that it is designed to be used.

There is no difference for the consumer… you still sight in the same and the adjustments are the same; however, you’ll be more in the center of the scope & you’ll be far less like to run out of travel at very long ranges if you use a 20 (or more) MOA base.


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[JDMBEND]

There really isn’t a downside for the consumer, but it adds a layer of complexity for the manufacturer. If the scope and the bore are parallel, the crosshairs will always be below the optical center of the scope beyond 100 yards, the further you shoot, the more pronounced this is. Theoretically, the scope is clearest at the optical center (not such a huge issue on higher quality scopes). Additionally, windage adjustments can get squirrelly at the furthest extents of the elevation travel (not such a huge factor with modern scopes). Using a 20moa base keeps your adjustments above optical center for the first (approximately) 700 yards & below optical center beyond that… closer to center throughout its effective range.

On systems with very slow moving projectile, we design this offset directly into the weapon so the scope is optically centered at the median distance that it is designed to be used.

There is no difference for the consumer… you still sight in the same and the adjustments are the same; however, you’ll be more in the center of the scope & you’ll be far less like to run out of travel at very long ranges if you use a 20 (or more) MOA base.


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Thank you for the explanation.

 

[nm.otter]

On systems with very slow moving projectile, we design this offset directly into the weapon so the scope is optically centered at the median distance that it is designed to be used.

There is no difference for the consumer… you still sight in the same and the adjustments are the same; however, you’ll be more in the center of the scope & you’ll be far less like to run out of travel at very long ranges if you use a 20 (or more) MOA base.

Translation: For a modern centerfire rifle, optimal rail tilt might be something like 5 MOA.