Just fininshed my SPR clone.  Have a cheap Smith and Wesson 3.5-10x50 mounted for now.  What ACOG is calibrated for a 18" barrel?  Does it really matter?  Any other optic suggestions?

Leupold or Nightforce not an ACOG.

Got it.  Any suggestions on model?  Low power or high power magnification?  I am mostly an iron shooter and just graduated to red dots.  Don't know much about optics.

nightforce!

Some thoughts...

Neither the M/RT nor Nightforce has a first-focal-plane (FFP) reticle.   So if you're planning to use the reticle demarcations as the primary mechanism for hold-over beyond the point-blank distance, it will only work at the one set power (the max power on the two named scopes).  

For example, if you get a mildot reticle and know that you hold 1.25 mils high at 300 yards, the scope must be set at  9x for the M/RT or 10x for the NF.    If you left it dialed at 3x or 6x because you were shooting for speed, your hold-over will be grossly wrong and you will miss.

A FFP scope such as the SB Short Dot, the SN3, SN4, or the one new model of Leupold MK4 has reticle features which demarcate the same angular distance on any power setting.   It will appear to "shrink" and "grow" as the power of the scope is adjusted.

Dialing for elevation with an external knob is obviously not affected by the scope power, so FFP vs. non-FFP makes no difference if you dial elevation instead.   If you choose this route, it is critical that the elevation knob has some visual or tactile indicator as to which revolution the knob is on.  Few things suck more than being one full turn off and not knowing it until you miss your target by 6 feet.  

The Leupold M1 knobs have hash marks indicating the revolution.  The M3 knob has only one turn so  there's no question.   The SN4 has indicators.  The SN3 with EREK can be set up with a tactile indicator (ie, zero stop).

I don't believe the Short Dot has any indicator.    As far as I know, the NF 2.5-10x also has NO INDICATOR.

If you only want to use the scope primarily as a visual aid, and just shoot within the point-blank distance for your target sizes, then it doesn't matter.

To answer your question about the ACOG..   Pick whichever TA31 or TA11 model suits your fancy.   I prefer the TA11 for its flexibility.   You'll have to shoot your loads from your rifle at each distance to figure out your particular dope anyway, so the calibration doesn't matter too much.  It will be within 6" at 400 yards in any case, depending on environmental conditions as much as changes in muzzle velocity.

Here's how I'd break it down for my own use:

ACOG if I wanted something super simple, for shooting targets no smaller/further than a 10" square at 400-500 yards.  That's getting to the limit of what you can visually resolve through the ACOG.    It will be better than any other of the following choices at close range (with the possible exception of the SN4 and SB, which would give it a run for its money),  and it will rule medium targets to 300 yards due to the super bright reticle.  The tritium works great at night.

M/RT if I wanted something still compact and more precise, and I was willing to dial elevation as the primary means of holdover.  It will be super slow close-in, and OK mid range.  

The NF2.5-10x I don't really get.   The knobs aren't set up for dialing due to limitations detailed earlier.  The reticle - whichever you choose - can only be used for holdover at the specific power (max) which is sometimes not what you want to use due to speed and field of view, and the shooter can forget to reset it before using it for holdover.  

The SN4 with the right reticle can do what the ACOG can do, but with more optical clarity, at the price of much more weight and size.    The SN4 reticle when lit is nowhere near the brain-grabbing intensity of the ACOG under daylight.    IF the SN4 went up to 6 or 8x, it would be much more useful IMO.

The SN3 (2-10x44mm) is superior to the M/RT and NF2.5-10x in all respects, IMO.   Better optical clarity; wider range of power adjustments; FFP reticle, more reticle choices.     The lit reticle is again not as bright as a ACOG under daylight.   This is a big and heavy scope, overpowering the AR15 platform if not doubling its weight (!!!).

I haven't shot the Short Dot 1-4x.   It has a FFP reticle and super bright illumination.  Look hard at this option.

hope this helps,

Zak

Quoted: Some thoughts... Neither the M/RT nor Nightforce has a first-focal-plane (FFP) reticle.   So if you're planning to use the reticle demarcations as the primary mechanism for hold-over beyond the point-blank distance, it will only work at the one set power (the max power on the two named scopes).   For example, if you get a mildot reticle and know that you hold 1.25 mils high at 300 yards, the scope must be set at  9x for the M/RT or 10x for the NF.    If you left it dialed at 3x or 6x because you were shooting for speed, your hold-over will be grossly wrong and you will miss. A FFP scope such as the SB Short Dot, the SN3, SN4, or the one new model of Leupold MK4 has reticle features which demarcate the same angular distance on any power setting.   It will appear to "shrink" and "grow" as the power of the scope is adjusted. Dialing for elevation with an external knob is obviously not affected by the scope power, so FFP vs. non-FFP makes no difference if you dial elevation instead.   If you choose this route, it is critical that the elevation knob has some visual or tactile indicator as to which revolution the knob is on.  Few things suck more than being one full turn off and not knowing it until you miss your target by 6 feet.   The Leupold M1 knobs have hash marks indicating the revolution.  The M3 knob has only one turn so  there's no question.   The SN4 has indicators.  The SN3 with EREK can be set up with a tactile indicator (ie, zero stop). I don't believe the Short Dot has any indicator.    As far as I know, the NF 2.5-10x also has NO INDICATOR. If you only want to use the scope primarily as a visual aid, and just shoot within the point-blank distance for your target sizes, then it doesn't matter. To answer your question about the ACOG..   Pick whichever TA31 or TA11 model suits your fancy.   I prefer the TA11 for its flexibility.   You'll have to shoot your loads from your rifle at each distance to figure out your particular dope anyway, so the calibration doesn't matter too much.  It will be within 6" at 400 yards in any case, depending on environmental conditions as much as changes in muzzle velocity. Here's how I'd break it down for my own use: ACOG if I wanted something super simple, for shooting targets no smaller/further than a 10" square at 400-500 yards.  That's getting to the limit of what you can visually resolve through the ACOG.    It will be better than any other of the following choices at close range (with the possible exception of the SN4 and SB, which would give it a run for its money),  and it will rule medium targets to 300 yards due to the super bright reticle.  The tritium works great at night. M/RT if I wanted something still compact and more precise, and I was willing to dial elevation as the primary means of holdover.  It will be super slow close-in, and OK mid range.   The NF2.5-10x I don't really get.   The knobs aren't set up for dialing due to limitations detailed earlier.  The reticle - whichever you choose - can only be used for holdover at the specific power (max) which is sometimes not what you want to use due to speed and field of view, and the shooter can forget to reset it before using it for holdover.   The SN4 with the right reticle can do what the ACOG can do, but with more optical clarity, at the price of much more weight and size.    The SN4 reticle when lit is nowhere near the brain-grabbing intensity of the ACOG under daylight.    IF the SN4 went up to 6 or 8x, it would be much more useful IMO. The SN3 (2-10x44mm) is superior to the M/RT and NF2.5-10x in all respects, IMO.   Better optical clarity; wider range of power adjustments; FFP reticle, more reticle choices.     The lit reticle is again not as bright as a ACOG under daylight.   This is a big and heavy scope, overpowering the AR15 platform if not doubling its weight (!!!). I haven't shot the Short Dot 1-4x.   It has a FFP reticle and super bright illumination.  Look hard at this option. hope this helps, Zak

I learned more about scopes in this thread than I have in a very long time.  Thanks for the time and effort, Zak.

Nightforce has zero stops on some leo/mil scopes... dont know why they dont offer that on their new scopes.