Very shortly I am planning a 20" rifle build.  I am looking for a LR scope.

Currently I have an M4 with a TA31 but I would like something with a lot more "zoom".  I was thinking about going into the 15x - 20x range.  

I don't think I will need a illuminated red dot since I doubt I will be doing any night shooting.  

Also I have no idea what leupold reticle looks like and I can't seem to find one on their website.

I was also considering a Larue SPR-M4 mount.  Will that give enough height for a large 58mm forward lens if needed?

Ya I can't figure out what mount because Larue doesn't have these on their website.

They have a SPR-M4 that is it.

I will probably go with a 15x

I have the NF 2.5-10x24NXS on my rifle. I have compared the Loopy LR/T 3.5-10x40 side by side and the NF beats it IMO. Differences are subtle but noticeable. I agree that 10x is probably the most you'd want for an AR. Any more and you'd probably want bigger objective which means more weight. The NF is compact for what it is and the glass is excellent. You don't think you need illumination but after shooting ad dawn o'clock, the ill. reticle was a godsend. They're not cheap good optics never are.  I highly recommend the Larue mount also. Here's my first build.

nightforce in larue spr mount

Quoted: nightforce in larue spr mount

That is probably what I will go with.

Have been playing with a couple mil dot Leupolds - one 4.5 x 14 that I got used for a great price and the other a 3.5 x 10 MK4 that got a year ago.

Always figured ten power is enough mag for reasonable sized targets from field conditions, which it is (all the big game hunting scopes tend to be 1.5 to 5 or 2.5 to 8 Leupolds).  However, when shooting off the bench or a good bipod, I end up liking the extra four power on paper or small targets (corner of the tannerite bottle during the monthly shoots).

Not that much difference in effectiveness of the 3.5 or 4.5 power shooting off hand (both are ok but less power would be better).  Have no experence with the NF but the 2.5 lower power makes an interesting option to cover a wider range of uses.

Leupold 4.5x14 scope in LaRue 1.5 upper (BUIS not installed in this image - ended up with Troy instead of KAC 600m which lives on the HBAR now).

do those last couple of pictures have some kind of scope extension on the lens?  They seem really long for some reason.

+1 to Mike at CSGunworks. That's where I got the scope above.

Quoted: +1 to Mike at CSGunworks. That's where I got the scope above.

where i got my nightforce as well