What is the difference between an 2" and 3" Cantilever. I bought a Vortex 3-9x40 scope. Vortex has 2 options. This is for the Sport II Rifle. Thank You....OldYooper

The 2 offsets allow for different ranges of eye relief. Big guys with long necks need to position the scope further forward than little guys with short necks. You want the scope turrets between the rings and your Picatinny rail is only so long. It's probably more critical if you're leaving a flip-up rear sight on the rifle, which further limits your range of positioning.

Do a layout on paper. Vortex has dimensioned diagrams of both mounts online. I suspect they have a diagram of the scope too. Figure you'll want the back of the scope about 3 to 3-1/2" away from your eye.

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The longer the cantilever, the further forward the scope is mounted. So, in your case, the scope would be mounted 1" further from the back of the rifle with the 3" compared to the 2" mount placed in the same spot on the receiver.

You might want to check out the USA made 1” offset Vortex Pro mount as well; that’s what I use and the ocular sits right over the charging handle.

It all depends on where you want the ocular portion of the scope to sit for proper eye relief and lack of interference with the charging handle.

My guess is that either a 1” or 2” offset will work for you.

I use a 2" on a 20", solid stock, AR. As you can see, there remains plenty of fore / aft space for any additional adjustments with both the optic and /or mount.