LooseRounds.com
5.56 Timeline
Weaponsman.com

Thoughts on zeroing

Having spent time in the military and working at a public range I learned that most people don’t understand zeroing sights or optics.

I always found it humorous when some of the regulars at the range would have a new rifle or new optic and invite me to come over and try their new gun. I’d fire a shot and tell them something like, “Cool rifle, but it is impacting 4 inches left for me.” The response I would get would be a coy line much like, “Well why don’t you go ahead and dial it then.”

I like to imagine that I keep all my firearms combat ready, but realistically I would never choose to use some of them in a fight. I wouldn’t grab the 10/22 for obvious reasons. While I would trust a Garand in a fight, it would be far from my first choice. One of the most critical things I think of as part of being “combat ready” would be the simple ability to hit what you are aiming at.

I like to think of the quality of a zero on a firearm as one of several states. I don’t think I’ve seen other people talk much about this, so I want to lay out what I think it.

  • Unzeroed
  • Mechanical Zero
  • Battle Sight Zero (BZO) or Reduced Range Zero
  • Fine Zero
  • True Zero (or proofed zero)

Unzeroed: The least desirable state for a firearm sights to be in. Hopefully an unzeroed firearm will impact close to where you aim, but there is no way to know with out test firing or checking the bore axis to the sights against a common index.

Mechanical Zero: The sight is centered either mechanically or optically. On something like a micrometer adjustable sight, mech zero may be obtained by counting the total number of clicks and adjusting it half way. On scope you could count clicks or use a mirror to get the crosshair centered in the tube. Centering a scope via scope adjustment may not be the same as optically centering.

Generally, one a well built firearm, mechanical zero will be close to right on. On cheaply built guns, not likely. If you have something like a rifle with a 30MOA canted base for long range shooting, the mechanical zero on the scope will deviate from a proper zero because of that.

It used that a brand new, out of the bolt, Colt AR15 or M16 generally didn’t need adjustments from mechanical zero when sighting in. But as of the last few years this no longer seems to be the case.

Battle Sight Zero (BZO) or Reduced Range Zero: There are all manner of reduced range zeroing techniques. Rarely you will see 10m zeroing targets. Often reduced range zeroing in militaries is done at 25m. For the longest time the USMC liked to use 36 yards for a reduced range zero on the M16A2/M16A4. The idea of a reduced range zero is to easily reproduce a longer range fighting zero at reduced ranged. It is easier and faster to zero at 25 meters than 300. Negligible effect from wind, easier to change and inspect targets, etc. The downside is that ANY minor error at this reduced range will be magnified at farther ranges. Say if a soldier was impacting 1 inch left at 25 meters, they might completely miss a hostile enemy at 300 meters. That could cost lives.

I consider a BZO an acceptable zero. I’ve found that with a 14.5 inch AR15 firing M855, if I impact 0.3 inches low at 25 yards, I will be right on at 300 yards. This lets me quickly and easily sight in any similar carbine at the very common distance of 25 yards. I used to have a scoped rifle where my 100 yard zero was 2.6 mils different from my 25 yard zero. I could dial up 2.6 mils and be right on at 25 yards. This allowed me to double check that zero with that gun at reduced range.

A BZO often won’t give you a perfect zero for the farther distance, but they should be close enough. The now common 50/200 zero is a good example. Zeroing at 50y or 50m isn’t going to give you a perfect dead on zero at 200, but it tends be close enough for practical work.

I would not hesitate to go into combat with a firearm that has a BZO. I would prefer a finer zero, but a BZO is functional.

Fine Zero: Simply put, a fine zero is zeroed at the range the firearm is intended to be sighted in at, and is adjusted as closely to being perfect as possible. A magnified scoped rifle might be fine zeroed at 100 yards. Something like a M16A2 or M4 Carbine with CCO would be fine zeroed at 300 meters. Often people going into combat never get the chance to fine zero and must just rely on a BZO.

Sometimes you are limited by the precision of the adjustments. As an extreme example, the leaf sight on my M203. Each click of the windage knob adjust the impact by 1.5 METERS at 200 meters. So if I fire a shot and impact 1/2 METER left of my point of aim, I can’t adjust closer than that. But a fine zero will be as accurate as precise as the sights allow.

A fine zero is preferred over a BZO as it will have removed any error from the BZO and have been tested out to the preferred sighting distance.

True Zero or Proofed Zero: You don’t tend to hear about this outside of precision shooters, longer range hunters, or snipers. People who have to shoot at multiple distances, or an unexpected longer range distance may take the extra step to true or proof their zero.

This is less about the zero, and more about the knowledge and preparation the shooter has made for long distance shooting. Truing or Proofing is finding out where exactly you will hit or the adjustment you need for the various ranges you might be shooting.

Simple example, I used to shoot 565 yards with a 4x ACOG. 565 yards is about 516 meters, so I should have been able to use the 500m mark in the ACOG. Instead, with my firearm and ammo I needed to use the 600m mark to impact where I wanted to hit. Had I only relied on the stock marking I would have always missed.

While I was in the Corps, when we shot the rifle range, we would note our true zero for each distance. Windage adjustment might change due to how we held our rifles, elevation might be slightly different as well. So one persons 500 yard zero might have been setting the rifle rear sight to 5, another might need to set their A2 rear sight to 5 plus 1 click.

You might have a great gun with an a great cartridge and your ballistic calculator spits out a hold over for some distance, but when you actually shoot that distance you may find you need a different adjustment or hold over. Accounting for that is truing or proofing your zero. With out proofing, that drop chart or BDC is just a suggestion, not a fact.

A very few ballistic calculators give the ability to put in your proofing results to calculate a corrected drop chart to ensure you will hit when you need to hit.


Not that simple, isn’t it?

10 Years Of The Colt 6940

It’s hard to believe to me now but its been ten years since the Colt 6940 came out officially for sell. It was a pretty big deal at the time because it had been a long time since Colt had come out with a new variant of the AR15. The monolithic rail and flip up front site were something colt teased for years before it got in peoples hands.

You can see the gun above has a lot in common with the final version of the 6940. The gun pictured was submitted to the military for a possible future adoption. The early versions had a much inferior sling mounting system for the rail. You can see the stud on the side of the rail at the 3 o’clock position.

Various versions of this gun was shown at SHOT shows over the next years and scuttlebutt always claimed it would be out “later this year.” That was optimistic to put it mildly.

One of the models shown along side of those was the Colt “M5” pictured below. We never saw that. Thanks God for small favors.

Around 07, word was let out that the Colt “LE1020” was about to come out. It was so sure that some distributors and dealers started taking pre-orders. The 1020 was essentially the early version of the Colt 6940Piston. It seems at the last minute it was cancelled and refunds issued. The reasons and story will have to wait for another day.

One of the curious things of the history is this tantalizing model that many wish would be brought out even to this day. The Colt 6945 it was called at the time. Though it never came out and the colt model number was resused for another model, the 10.3 inch barreled 6940.

I am sure most of you reading this will immediately see this and wonder why it was not sold. No idea. It can be ordered this way if you are a LE org or the military, but so far that’s it. You can see the older style sling stud. As I said, the 6945 name went to another gun. Which Howard, lucky bastard that he is, owns an example of. Pictured below in all its glory.

Of course it is not the only SBR 6940 based gun. There is a 11.5 inch barrel and a 15.5 inch barrel. Also there was this little gem. The Colt SCW with a side folding stock.

In 2009 the LE6940 we now know came out and of course I got one nearly immediately. I was not let down. Since then I have been a 100 percent convert on the Colt monolithic upper. I think it is a major improvement to the gun and its accuracy is outstanding.

The 6940 in its stock form with match quality ammo and an optic makes an amazing and handy small precision rifle. I used this combo to shoot crows all summer out to 300 yards. There is just something immensely fun about shooting a carbine with a high magnification precision optic.

Over the next few years I used the 6940 constantly.

A few years later the 6940P finally came out after years of waiting. Below are the DI and Piston uppers compared. It is a very nifty design. The P comes with a SOCOM profile barrel and H2 buffer along with the piston operating system.

A full look and review of the 6940Piston can be found here on the site already so I won’t cover that again.

Since then a few other versions have come out. Noticeably the 7.62×39 variants for other countries who prefer to use an inferior service round.

You may have noticed the top picture shows a version that takes an AK magazine. That has been a foreign military sold model only at this point and it’s likely to stay that way.

Most significant to the spin off monolithic upper series is of course the 308/7.62NATO carbine 901.

Now after all this time. How does the regular old DI gun shoot? Still great. The free floated barrel and the unique system that attaches the barrel is incredibly accurate for a gun with a milspec barrel. Not to say they aren’t already more accurate than most people realize, but the free float monolithic upper brings it all out with match ammo. I placed 10X optic on my 6940 and shot some groups with it at 100 yards to show a general idea of just what they are capable of .

The carbine was shot from the bench off of bags. The leupold 10X was used and the SSA match trigger were able to make shooting a breeze. Really there is not much difference in accuracy between this and my MK12.

a selection of handloads and the more high end factory ammo



“flyer” is zeroing shot not part of group


The Colt 6940 is a real classic in my opinion and I have turned a lot of people on to them. No one I know has regretted buying these excellent carbine once they get them in their hands. It is a great gun now 10 years old and going and I highly recommend them.

Optic of the week: Leupold MK6 1-6 CMR-W 7.62

This is the most awesome optic that I am not going to recommend.

I’ve been selling off some of the stuff I wasn’t using. I ended up getting this scope in trade for a scope I wasn’t using and wasn’t going to use. I wouldn’t purchased this scope outright, but now that I have it, I really love it.

The MK6 1-6 is kind of an odd duck. It is most often seen with the CMR-W reticles which are most like an ACOG BDC with addition milradian hash marks and wind hold marks. It has a very bright daylight visible illumination, great turrets, an awesome 1x setting, a really nice battery cap, etc. But the list price is insane, and it is build for to be used in a way that I think makes it less preferable for most people.

There are two issues which I think makes the MK6 1-6 the wrong choice.
First is cost. MSRP is $2859.99
I’ve seen them sold used, with a mount for less than half that. Even so, that is pricey. While this scope is great, I wouldn’t pay that much for it. I only have once because I traded a much cheaper scope for it.

Second is the role of the scope.
There is a spectrum between speed and precision. A reflex sight is built for speed, and that 42X bench rest scope is built for precision. As magnification increases, users tend to want something geared more towards precision. This scope has a course BDC reticle and coarse adjustments, it is more like an ACOG+ than a mini-sniper scope. Most people I’ve talked to would rather have a mini-sniper scope these days. Now we have all sorts of new 1-8X and 1-10X that better fit that role over this scope. It is as if this scope is obsolete before it came to the market.

The glass is imported, so it doesn’t say “Made in the USA” I’ve yet to meet someone who doesn’t agree that foreign glass is better.

The turrets on this scope lock at zero and have a button to release them. If you press the button and turn it away from zero, they are no longer locked and you can turn them normally. Each click is clearly felt and barely audible. I found it really easy to set the zero on these as once I loosen the cap, turning it to zero locked the rotation, allowing me to just re tighten the screws. I would be perfectly happy if all my scopes had turrets like these.

These scopes turrets are .2 milradian adjustments. So about .72MOA per click. This allows the user to dial in up to about a 900m zero in a single turn, but also clearly shows that this is not a scope for precision shooting. I don’t think of this as a downside, but it is certainly an unpopular choice.

This is the best scope at 1X I have ever used. It felt the most like an Aimpoint than any other.

If you are properly aligned with the scope, the illumination is amazing. At 1X it is the flattest, nicest, most Aimpoint like view I have seen out of a magnified scope. But due to the lighting system this scope uses, if you are slightly off axis it dims greatly.

Lined up and the reticle is very bright
Move your head slightly and it dims.

The CMR-W BDC reticle is in meters. The 5.56 version goes to 900m (about 984 yards) and the 7.62 version goes to 1200m.

The center dot is for 200m. To the left and right there are mRad hash marks and a mRad vertical scale on the left. Along side the bullet drop chart there are wind lead marks for 10 and 20 mile per wind hold. Also on the left side of each distance there is a range finding tool.

A side note, I highly recommend when you are zeroing a scope, that is new to you, to start at close distances. This scope is was set 9 inches low at 25 yards. Had I started at 50 or 100 yards I would have been well off the target.

The battery compartment has a recessed button and flips open

The battery compartment makes for easy and fast battery changes and removes the chance of cross threading a cover back on. For the optics with short battery life, they all should have battery compartments like this.

The 20mm objective lens looks tiny in the 34mm tube.

I really enjoy shooting with and using this scope. But I do not recommend anyone buy one. Doubly so at list price. Optics design and tech is rapidly advancing. Now there are cheaper and smaller 1-8X scopes like the Nightforce NX8. When I first used the MK6 I thought it felt heavy and clunky. I was sort of surprised when I read it is the same weight as some much smaller scopes I own. It isn’t really heavy for what it is, but it is large. I think it feels clunky and overkill for an AR15, but less of a long range precision scope than you would want on a .308 Semi Auto.

It is a great scope, but if I was spending fresh cash, I would rather spend far less cash on newer scopes.

Inland MFG M3 Carbine

We have seen a few really nifty M1 carbines out of Inland the last few years. It was just a matter of time before they offered us the version the least known or seen. The M3 was the variant done up to mount a huge active IR night vision “sniper” scope and a huge battery to run it. It didn’t really pan out at the time but it’s existence did mean the carbine Colt version of the M16 would forever be known as the M4.

Now, if you add some normal day time optic to the handy little carbine that is another story. Above you can see the base/ring mounting system Inland has developed for the mounting of optics. Simply put, the base uses the redfield/leupold turn in front ring and dual windage screw rear ring system. any rings you want to buy that work in this manner will fit and work. And it works really well. I chose to put a vintage Weaver K4 on the gun as it is more evocative of the time period this gun had its short heyday.

The machine work Inland put in on this is kinda of amazing. My friend and partner in crime when it comes to our more insane long range shooting ideas is an experienced machinist and when I showed it to him, we both at first thought the base was part of the receiver and machined into shape. It took a surefire light and a closer look to see that it was indeed not part of the gun. It really is a beautiful job.

One of the things that sticks out on the M3 was the cone flash suppressor. Inland did not forget this iconic attachment. And it is attachable. As you can see above it is a simple system. You can chose to put it on or leave it off. I found it did not really impact accuracy any amount I could determine while on and shooting at ranges the 30 carbine round was meant for. There was slight changes when shooting with our without though and depending on the mood or whichever gun you may have, the amount of re-zeroing could vary. I did not bother to re adjust the optic as it was less than 3/4 inch impact change and I was shooting for groups and location on the target did not matter to me.

As expected, being able to use some magnification helped with group size at longer ranges. The Inland M1s have been accurate for me over years since starting to test them.

Group above was shot off bags from bench at 100 yards. The group is a 10 round group and the one flyer I offer no excuse for other than I just touched it off without being ready. The group below was fired at the head at 150 yards.

All groups were fired using federal soft point LEO ammo. I have no idea where I ever got this ammo from but it is pretty accurate. Unfortunately I used all I had left for this test. Target below was fired at center body of target from 300 yards. With the optic it was pretty easy. It is still a carbine meant for combat but I can’t imagine anyone with any sense really having much to complain about its performance at this range. But I am sure some one will in the comments.

Hey, what more could you ask for considering the limitations of the round? Pair the optic with a Korean era 30 round magazine and you got one heck of a neat little carbine for something. Walking around the farm shooting ground hogs or maybe short range coyote gun. With proper bullet selection maybe even white tail at shorter ranges. I don’t know, your imagination is the limit. It doesn’t need justification if you want it. if you think it’s neat then buy one. The quality won’t let you down, nor it’s looks.

I apologize for not having a full glamour shot of the gun with optic for this review. Something went badly wrong with my camera during the uploading process. The camera decided to die after 9 years and it took the remaining pictures with it. This includes the rest of the groups shots and the glamour shots of the gun posed with period militaria collectibles and all that crap you are used to seeing when I do these. That is also why this review seems shorter than normal. It’s not just your imagination or my laziness. I have been trying to recover those photos and if so I will update this review ASAP. To add to that this was the first time I didn’t bother to back up every picture by taking the same pictures with my Iphone just in case.

Optic of the week: HK Diopter BUIS

Ok, I’m phoning it in this week.  I found these old HK BUIS I thought I sold long ago, and I found that the old article on them has all the images missing.

On the HK416/MR556 and their .308 rifles as well the optics rail is higher than the rail on a standard flat top AR15.  Because of this HK fixed iron sights are lower than standard height AR15 sights so they can not compatible to use together.  Not that you would want too.

Under the 200m aperture of the drum, there will be 1 or 2 dots.  If there is a single dot (like this one) the sight is calibrated for a 10.4 inch barrel.  If there are 2 dots, it is the model for the 14.5 and 16.5 inch barrels.

HK Front sights are not adjustable, all zeroing adjustment is done on the rear sight.

The drum apertures are different sizes and set for 100 to 400 meters.  The 100m opening is much larger than the other ones to make it easier to use for close quarters use.

Windage is adjusted by loosing the screw on the top of the sight, and turning the screw on the right side of the sight.  1 full turn will move your point of impact 6 inches at 100m.  Tighten the top screw to lock the sight back in place.

Inside the drum there are two tabs.  Compressing both tabs inwards allows for the drum to turn adjusting the elevation of the rear sight.  You need to turn the elevation drum in 1/4 turn increments for 1.5 inch adjustment at 100m.  If you don’t have the proper sight adjustment tool, you can make adjustments using a pair of needle nose pliers.

Zeroing these sights can be annoying.

They are nice sights, and if you are more familiar with HK style sights than AR sights, it is nice to have this option.  However you can get good AR sights for cheaper that will have a finer and easier adjustments.