Hello,

I want to buy a optic for my M4 and I think the TA31RCO-M4 is the best. But is it better to buy the TA31F because the TA31RCO-M4 is build for the M4 and I can't use it for other rifles?

You should be able to, many people mix and match their optics and rifles.  From what I understand, the BDC isn't going to be that different as to preclude its use on another rifle with slightly longer barrels.

who cares, get which ever and use the bdc tacked above.



thats the only difference between the acogs is the bdc and reticle

Thanks for the reply's.

I have the RCO on my M4gery. It is a great scope. One advantage of the RCO is that is has the tethered adjustment caps. If you have ever tried to keep up with the small ACOG caps at the range, you will see the advantage.

The RCO has a slightly busier reticle (which I actually prefer). There are black lines on each side of the chevron.

My dealer told me that the RCO would likely have a higher resale value due to its military usage. You really can't go wrong with either scope.

TA31F, TA01NSN, Reflex, etc. all have seen military usage, it's the demand that drives new and resale prices

Plus the RCO comes with a nice case too.

Correct me if I'm wrong, but isn't the TA31-F for a 16" bbl and the TA31RCO-M4 for a 14.5" bbl (both calibrated using M855 and a flat top mount)? If that's true, the differences on the bdc should be negligible, but if you're really particular, it may be an issue.

Quoted: You should be able to, many people mix and match their optics and rifles.  From what I understand, the BDC isn't going to be that different as to preclude its use on another rifle with slightly longer barrels.

I have an MGI QCB flat top upper with a 14" 5.56 NATO 1/7 twist barrel on it right now.

I am also getting some sort of heavier, longer range, long barrel for it (have not decided which one yet).

I will probably fire M193 in the short bbl and some kind of heavier, match round in the longer bbl.

Between the Trijicon TA31RCO 16”, the 20”, and the TA31F, which of those three do you think would be the best all around optic?

If I were pressed at this point to pick where I would want to have the optic “right on,” and where I would use a little Kentucky compensation, I guess I would want the optic functioning properly at the longer ranges with the longer barrel, and then I would compensate accordingly with the shorter ranges and bbl.

I’m no expert and I am open to getting an education, comments, etc.

P.S. Comments on a flip up rear BUIS would also be appreciated.

Thanks in advance for any help you might provide.

I'd get the TA31RCO, not because of the additional referencing stadia lines but for the case and adjustment caps.  I have a TA31, TA31F and TA01NSN, the TA31F is my favorite.

Quoted: I'd get the TA31RCO, not because of the additional referencing stadia lines but for the case and adjustment caps.  I have a TA31, TA31F and TA01NSN, the TA31F is my favorite.

I guess they make the TA31RCO for a 16 and a 20 inch bbl.  According to a post in this thread, they are all calibrated for the M855?  If that is true, and if I got the one for the 20", I wonder how far "off" my sight picture would be on real close in work with M193 ammo?

I also notice you can buy factory installed "External Windage"and "External Elevation" Adjusters.  Are there *internal* adjustments on them too?  I thought they were all just "set" and that is what you had to work with.  The web site doesn't give much detail.

Thanks for your response.

There are windage and elevation turrets.  The RCO model has turrets that can be manipulated without taking off the twist-off caps normally found on other ACOGs, so they're faster to adjust.  But as you've guessed by now, ACOG can be adjusted.  I dunno of an optic that can't be, some are clunky like ELCANs but without being able to change elevation and windage, an optic would be pretty useless

I guess that's where my confusion came in on these things.  I've never seen an optic that was not adjustable.  So when I read about these ACOGs being calibrated for a specific round (i.e. M855, etc), and people talking as if they would be hard to use on other weapons, or for any other ammo, I didn't quite understand what the big deal is.

Just zero the optic.

Unless, of course, people are just talking about the different elevation reticles inside being pre-set elevations for different distances *after* you have adjusted for zero.

I guess I need to actually look at some with the factory installed external adjusters attached to see what the difference is compared to a site without them.  They are listed as "accessories" so I assume the optic comes without them also.

Again, thanks for holding my hand on this.  I have done a "search" but haven't found these particulars discussed elsewhere.

The bullet drop compensator may be different, but MOA is still what it is regardless of barrel length

Ok the simple answer is this:

TA31RCO-M4 - Bullet Drop Compensator Calibrated for a 14.5" barrel, firing a 62 grain bullet, inludes horizontal lines in reticle, inludes knob cover tether

TA31RCO-A4 - Bullet Drop Compensator Calibrated for a  20"" barrel, firing a 62 grain bullet, includes horizontal lines in reticle, includes knob cover tether

TA31F              - Bullet Drop Compensator Calibrated as an average between 14.5" and 20" barrel, firing a 62 grain bullet, does not include horizontal lines in retical, no knob cover tether

The Horizontal lines in the sight picture are in place so USMC team leaders can reference and direct targets to the team, ie target is 3 and one half spaces left of the vehicle behind that brick wall.

The difference in accuracy, in this case "elevation of point of impact" is negligable up to 300 yards.  Beyond 300 yards it is variable based on choice of ammunition, barrel twist, barrel length etc.  But as a general rule if you were to place say the TA31F on an AR with a 20" barrel it would be approximately 1 MOA off in elevation, or 5 inches at 500 Yards.

If accuracy matters to you at varying distances than my advice would be to match the ACOG to the weapon.  If you are never going shoot beyond the 300 yard line than you should be able to use the less expensive choice without really sacrificing accuracy.

Hope this clears things up for you

I want to know which of you guys is using your ACOG to shoot things beyond 300 yards and what kind of results you are getting using the BDC and why you are doing it.

Why?? Because it's fun

So far, 600 meters w/ 20" flattop and TA31RCO-A4 using Lake City M855. PERFECT as far as zero from 100-600 meters. I used a rangefinder to measure the distance. I can't wait to take it all the way out to 800. I expect to hit the torso of a man-sized target at least 75% at 800. I was 9 for 10 at 600.