I am putting together a reasonably lightweight 300 WSM and am considering either a 2x7 or 3x9 lightweight Leupold scope.
Is there any noticeable difference in the optical quality between these and there regular models which weigh 3-4 ounces more?

No, go 3x9. Weight becomes an issue on .338 and bigger caliper.

It should be just fine....the objective lens will be smaller but will still maintain exit pupil diameter from 5-6 power down in very low light conditions. Good choice for a lightweight rifle, I would opt for the 3x9x33.

woods

First, I really like the Leupold Compact (now called "Ultralight") line of scopes for smaller, lighter rifles. I have them on .22 Rimfires, centerfire .22's, and even one on a .308.

That said, there are optical compromises in building a smaller instrument. The eye window is slightly more restricted on the Compacts, and the eye relief and field of view is slightly less than on the "regular" size scopes. The body length on the 2-7 restricts it to rather short actions and it may or may not mount appropriately on your WSM.

If you are considering a 2-7, I would suggest the regular VX-I or VX-II 2-7. It is still extremely compact as scopes go and is so little more in weight and bulk as to be irrelavent on your WSM.

Good points about mounting. I will have to put the Talley bases on and do some measuring before I place an order. But at this point I am leaning towards the 3x9 lightweight. Every ounce counts!
I appreciate the feedback so far.

Just curious, what are the weight differences between the regular and compact's in the two scopes?
I read a post on another forum stating the things Stone mentions, and they are definitely something you, the buyer, should look at before making the purchase. What would be best is if you could do a side by side comparison of the different scopes.

Don

Approximately 4 ounces. About the same difference between the regular and the short action weights.
I used several compacts in my day and didnt realize the newer "lightweight" models were essentially the same thing. I was happy with the compacts.