Backup rifle sights - some useful things I've learned

As part of my project to upgrade some of my friends' rifles, I've been looking into some of the latest "game" techniques (specifically for 3-gun competition), trying to get a sense of the state of the art, and what can (or should) carry over from competition to actual defensive use.  My recent three part series of articles on AR-15-type personal defense rifles grew out of that project.

I've long been a fan of backup iron sights on a defensive rifle, co-witnessed through the main optical sight, so they can be brought into action quickly if need be.  However, I've now noted that most competitors in 3-gun competition have moved to offset backup sights, mounted at a 45-degree angle to the normal line of sight.  A quick twist of the rifle at their shoulder moves the main sight off to one side and brings the backup sight(s) into line, allowing them to "stay in the fight" if something goes wrong with their primary unit.  I've known of the existence of such offset sights for a long time, but I've not used them, because of the ease with which they can strike and/or get caught on obstacles while moving through confined spaces.  That can not only snag the rifle and slow your progress, it can even knock them right off the gun unless they're very strongly mounted.  That's hardly an optimum situation.

Three factors are causing me to reconsider my earlier, negative opinion about offset backup sights.  The first, below, demonstrates that if the front and/or back lenses of the primary sight are affected by weather or debris (i.e. sand, mud or what have you), co-witnessed iron sights will suffer from the same problem.

I should have thought about that issue myself:  but in my days in uniform, we didn't have optics on our battle rifles, so the problem didn't arise.  I'll be interested to know how often it occurs in action in today's military.  If any reader has experienced it, please tell us about it in Comments.  I can also see that, if opaque protective caps are in place on the primary optical sight, that will render the co-witnessed backup sights useless too.  If the rifle has to be used in a hurry against a sudden threat, angled backup sights won't suffer from that problem, allowing you to respond faster and more effectively.

Another video, below, shows how offset backup sights can be easily and accurately zeroed by using an offset bipod to aid in the process.  That's not a solution I'd thought about, but it's a very good idea.  As soon as I saw it, I tried it with one of my own bipods, and found it worked well.  (See further down this article for offset rail mounts for that purpose.)

The third factor is the problem of getting backup sights snagged on obstacles, and either jarred out of zero or knocked completely off the rifle.  This remains a problem:  but I note that there's now a plethora of steel (rather than plastic) angled iron sights out there, at much more reasonable prices than I've seen in the past.  They may be tough enough to deal with that problem.  I'm used to Magpul asking well into three figures for its MBUS Pro offset sights (shown below), which until recently appear to have dominated the field.

However, there are now many competing offset backup sights at much lower prices.  I can't comment on the quality of most of them, as many appear to come out of China and to copy each other's design.  I tested a couple for my current project.  The clear winner (so far) has been Acme Machine's 45 degree offset sights, shown below.

They're fully adjustable, made of steel, and look and feel plenty tough enough to stand up to their task.  What's more, they're on sale right now at only $14.99 per pair, which is a bargain in anyone's language.  (No, Acme isn't paying or compensating me to shill for them:  I just like to let my readers know about bargains when I find them.)  After testing them, I've ordered half a dozen sets to mount to my friends' rifles.

Many 3-gun competitors use offset-mounted optical sights (red or green dot units) for backup purposes.  That may be fine in a sporting environment, but I don't think they're optimum on a defensive rifle, for three reasons.

1. Any bad conditions that muck up your main optical sight are probably going to do the same thing to your backup optical sight.
2. Optical sights are typically not as tough as iron sights, and may be disabled by hard knocks against obstacles.  Standard sights are less likely to be put out of action that way (although they may need to be re-zeroed).
3. If batteries are going to fail, Murphy's Law tells us they'll fail at the worst possible time.  I don't want something as critical as a backup sight going out of action for that reason, just when I may desperately need it!  Iron sights don't use batteries.  Q.E.D.

Therefore, I won't be using or recommending optical sights as backups on my friends' rifles.

I also note with interest that offset backup sights aren't necessarily restricted to AR-15-style weapons.  I put a set on a Marlin lever-action 1894 carbine for test purposes, and they worked just fine.  I used one fitted with an XS Sight Systems scout rail, illustrated below.

The backup sights hanging off to one side looked odd, compared to what we expect a traditional lever-action rifle to look like, but they functioned just fine, and a red-dot sight snugged down between them with plenty of slots to spare.  I imagine a normal telescopic sight, mounted in high rings, would do as well, with enough height to clear the relatively low, flat mounting clamps of the offset iron sights.  So, if your preferred defensive rifle is a lever-action weapon (which isn't a bad choice - it's as effective today as when the Winchester was the "assault rifle" of its time, back in the Old West, and helping Turkey to smash a Russian offensive at Plevna in 1877), you can still have backup sights if you want them, provided you can fit a long enough Picatinny-style sight rail to accommodate them.  Such rails are also available from XS for some other rifles and shotguns, although generally much shorter, and other manufacturers offer them too.

The only caveat I'd add is that for offset use, steel sights are probably the best choice.  I've often used plastic sights like Magpul's MBUS units as in-line backups.  The plastic units aren't nearly as strong as steel ones, but if they're folded down out of the way most of the time, they don't take much punishment;  and their lighter weight is an asset when you're trying to shave ounces off a fighting rifle.  However, if they're going to be stuck out to the side of the weapon, where they're more likely to hit obstacles, their plastic construction is unlikely to be tough enough to withstand it.  I therefore suggest that they're best reserved for in-line use on top of the rifle, where they're better protected against such impacts.

What zero to use on backup sights?  I use 50 yards.  For an AR-15 style rifle, a 50-yard zero will hold on target anywhere out to 200 yards, which is about the limit for effective use of iron sights for most of us (particularly for older eyes - I daresay my actual effective limit is half that by now).  Backup sights aren't designed to take down an enemy at 500 yards.  They're to deal with an immediate problem, one so imminent that you don't have time to fix your main sight.  Such threats aren't likely to be far away.

Finally, if money is tight, there's a low-cost solution.  Simply switch your existing backup sights from the top of your rifle to a 45-degree offset angle rail mount.  There are many of them on the market (I've used this one with no problems:  they come 3 to a pack, so they cost less than $5 apiece).

You can mount your existing sight on that rail, and have all the benefits of an offset sight without having to spend more than a few dollars on the mount.  If you really want to mount an optical red- or green-dot sight for backup use, they can accommodate that, too.  Just remember to use blue Loctite or a similar product on the threads of their screws, to keep them in place, and don't over-tighten the screws, which might strip the threads.

Peter