I am getting into night vision and reading about how some of todays slim MLOK rails flexing even with the use of sling. Enough to mess with the zero of an IR laser mounted on the rail. Does anyone have any personal experience with this? I am in the market for a rail for my 11.5" pistol and plan on hanging a MAWL on the end. Will a slim MLOK rail be fine, or should I look more towards a quad rail like LaRue?

What does the Sig Forum brain trust say?

I'm not sure exactly what you mean with the "flexing even with the use of a sling" do you mean the sling might prevent it flexing or do you mean flexing because you are using the sling for shooting support.
In any case I use a sling to carry a rifle (and for the moment since we are talking IR lasers I'm discussing tactical rifles). I don't use one for support while shooting. Its not relevant to me in this kind of NV shooting and I can't imagine it is to anyone else either. This is short range speed matters type of use. I can imagine that the non free floating versions (like the KAC issues one and others) might be able to have issues with enough pressure on the rail, but I can't imagine that the newer quality free float forends give a damn about sling or any other kind of pressure. I use Geissle and DD and there is not a chance you can put enough pressure on them to matter. No matter where and how you put it. I've ended up with them against barricades and solid rests with really large amounts of pressure (cause I'm old and not flexible and course designers don't care) and it doesn't matter.
And I seriously doubt that going picatinny fixes any of that. Sure there is more mass in the foreend but the weak point is the attachment method. IN any case my advise is get a top of the line free float handguard that meets your needs and you will be happy.

There are mlok rails built well enough to be up to the task. Geissele and Hodge come to mind as units specifically made with aiming lasers in mind.

Don't go with something designed to be easy/cheap to make, or fancy styled, or as thin/light as possible and you're probably on the right path.

The easy answer is to stick with a chonky quad rail. But even there, go with something cheap and your chances of having a bad time increase, so you're still talking Daniel Defense, Centurion, etc.

For an 11.5" setup, the ~10" rail isn't going to be too bad of a boat anchor, either. Most Mk18-type rails will fit well, and there's a load of them out there used but plenty serviceable.

SOLGW is rolling out their M89 rail right now. It's a Hodge Spine Lock with a revision to the barrel nut and mounting for increased mounting strength, called the Drive Lock. There might be a 10.5" on the shelf right now or soon if you poke around online. This is larger than the "slim" wedge lock/Mk16-sized rails, but still a slimmer rail.
https://aimsurplus.com/sons-of...m89-m-lok-handguard/

How much flex are we discussing?
Tight sling pressure on a handguard in the prone for engaging targets at 600 yards is one thing, but if it’s a man-sized target at 50 yards (a long way for a laser) or even 100 yards (a really long way), how much would the beam have to be deflected to matter?

This isn’t a challenge to the idea, but a serious question that I’ve never considered before, so I’m curious what people’s experiences have been.

I no longer have a proper weapon mount laser, but I may have to tape a pointer to a couple of my ARs to experiment.

The point of a free float rail is to divorce the pressure of a sling to keep it from flexing a barrel. The older set up was a sling attached to the FSB sling swivel and that is what caused the barrel to bend.

Free floats aren't designed to be perfectly flex free, and if a front BUIS is mounted and you sling up tight you can see for yourself how much flex that setup will achieve. It will pull the front sight off the point of impact.

The free float was adopted to mount about 87 different items on it for use by different MOS in four different services. Lights or lasers on them won't aim in precisely the same axis if there is stress exerted on the rails.

Since there are few charts and too many configurations, each needs to be checked on it's own. Mount a laser on the float, one in the chamber, apply pressure, see how much things move. Firearm in a rifle rest aimed at a wall ten feet away should do. The results can be literally measured and some simple math to convert ten feet to 100m for MOA.

Use of a sling requires the aiming device to be located on structure other than what the sling attaches to, or the willingness to accept the results.

Thanks for the replies. I have an Aero Atlas r-1 currently, but that rail sacrifices for a lot of weight savings. Once I get my laser in the mail, I'll get it attached to see how much/if a problem exists with poa shift. I may go ahead and move my sling attachment as rearward as I can.

quote:

Originally posted by carriganzl:
Once I get my laser in the mail, I'll get it attached to see how much/if a problem exists with poa shift.

If you do, please keep us posted. It would be interesting to know.

I shoot a carbine with a laser pretty regularly, but not at any extended ranges or off of barricades that would induce a shift. I also don't use free-float rails. The more I type the more I realize the only commonality is the use of a laser on a carbine.

I agree with comments saying that it's likely not worth fretting much about. A practical carbine should be built ruggedly from the get-go, and whatever rail that's on a rugged practical carbine is likely more than adequate for the laser task.

This message has been edited. Last edited by: KSGM,

Midwest has their "night fighter" series with longer barrel nuts, more solid mounting, and less flex.

Hodge (and I think Hodge-based ZEV's) is unique being made from 7075 Aluminum alloy instead of 6061. Stronger and more rigid. Hadn't heard about the SOLGW version.

I use Geissele MK16's now. Yes I know about the MAWL drop test issue.

Barrel mounted non-free-flat quad rails did best in drop testing vs. loss of zero for lasers. If night vision is the primary use, it's worth considering, but then you don't have much space for your support hand and have to use a vertical grip.

Perhaps an optic mount with a built in IR laser to get it on the receiver and under the optic could be designed? Might require the optic to be up at 1.93" but would solve the entire issue of handguard flex.

I have two guns with carbine-length non free float handguards, equipped with lights and lasers and pressure switches; I don't have to use a vertical grip. I think VLTOR made a drop-in rail that gave you real estate ahead of the FSB too.

Handguard flex isn't a huge issue, for me and my uses. There is a mount like you describe; at least I have seen images of one that someone is perhaps prototyping. Higher optics are becoming the norm anyway, it seems.

The issue existed before AR's - a bolt action with a floated barrel had the front sling swivel on the stock. A lever action had a barrel band which mounted the sling and it would affect the barrel more. One of the finesse points of a lever is to get the mag tube to take more of the stress and keep the band from touching the barrel as much.

I quit using a sling on a the M16A2 and the resulting sight in and qualification was a lot more accurate. Having shot a lot of .22 International in the late 60's the practices for Olympic Match dont always work in the field. The firearm has to be compatible for them to work, like using the roof to haul a pallet of sheet rock on a Civic.

I've built an AR with free float, it has disadvantages in the field - the tube rings like a bell in heavier brush, is cold to the touch requring a glove under 55 degrees, and for all that, you don't mount optics on the float - they are back on the upper rail where they aren't affected. All the float does is keep the sling swivel from bending the barrel, and not having a sling eliminates the problem too. A sling in the field is a bit of a snagmaster and hunting is more a practice of gun in hand, not over shoulder.

The next AR won't have a free float. A 2MOA gun is capable of holding a 6" group at 300 meters, the effective range of the cartridge I chose, and for that the 1,000 foot pounds of minimum force downrange is less. For live game, the group size including shift is more than good enough, I don't have lights and lasers on a legal hunting rifle in my state. What I see has happened is the Quad Rail of the M4 started a lot of marketing and the shiftless free float got a lot of print about how accurate it was, which is true. But it's also like saying your truck can accelerate to 60mph in under 4 seconds - traffic doesn't allow it in most metros, it's useless. Free floats have gotten oversold, the attaching holes became a marketing competition, and the artistic CNC/extruded rails a fashion accessory. It's a $125 sling swivel mount if that's all you attach, and I don't even bother. I'd rather have a user friendly composite handguard - which i the day was military spec. Me stomping around in underbrush and crisp fall leaves is noisier than clip in guards. We've gotten sold on a lot of 'stuff' on the AR and it's not all that.

quote:

Originally posted by carriganzl:
I am getting into night vision and reading about how some of todays slim MLOK rails flexing even with the use of sling. Enough to mess with the zero of an IR laser mounted on the rail. Does anyone have any personal experience with this? I am in the market for a rail for my 11.5" pistol and plan on hanging a MAWL on the end. Will a slim MLOK rail be fine, or should I look more towards a quad rail like LaRue?

What does the Sig Forum brain trust say?

I have a PAQ 4C on a free float rail and don't have any issues, but I am not slinging up tight to shoot that gun.

Mount the laser as far to the rear as you can to minimize deflection.

It wouldn't hurt to get a Larue rail if you wanted to be on the extra safe side.


You aren't going to be shooting extreme long range with a typical IR laser and NV goggles. The resolution just isn't good enough to get much beyond 200 yards.

You will probably need an IR illuminator as well to reduce blooming issues with the laser.

He did mention MAWL, so the illuminator is covered.

I agree with the limited range. I know a guy that hunts at long range in the dark, but he uses clip-ons and as high-powered an illuminator as he can get his hands on. Lasers can be effectively zeroed and used to engage past 200m, in a military context; if you're already being engaged, and you know all those folks downrange are bad, the laser will be fine. However, PID and discretionary shooting will not happen that far away, IMO, because of the NVG's resolution and any laser zeroing errors or possible rail deflection. I have not experimented with inducing deflection at any range; I am sure it happens. My lasers are admittedly not zeroed for precision shooting; I can hit a torso-sized piece of steel at 100m; I use the constant offset method of zeroing. I also use drop-in Surefire M73 rails on both my ARs with IR lasers; I don't use those rails for any laser-specific reason.

There is a night vision thread, here on SigForum, which may have some info you find useful, carriganzl. It isn't near as info-rich as other sources though.

quote:

Originally posted by carriganzl:
I am getting into night vision and reading about how some of todays slim MLOK rails flexing even with the use of sling. Enough to mess with the zero of an IR laser mounted on the rail. Does anyone have any personal experience with this? I am in the market for a rail for my 11.5" pistol and plan on hanging a MAWL on the end. Will a slim MLOK rail be fine, or should I look more towards a quad rail like LaRue?

What does the Sig Forum brain trust say?

If I’m reading this correctly, you’re worried about flexing the rail while using the sling?

Yes, being able to flex the rail is a thing. Whether it be due to use of sling, vertical fore grip, shooting from barricades, etc. There are things you can do to mitigate those issues, but at the end of the day, it’s kind of a poop sandwich.

I have 2 rifles with FF rails. They both have the same style BUIS, KAC 300-600M. V7 keymod rails on semi-precision setups. I have purposely tried to induce rail flex while zeroing the irons using an Atlas bipod. It’s doable but I had to put a lot of force into the bipod to cause the issue. My sling mounts are set far back towards the chamber to reduce the impact of flex using the sling as support. I cannot cause deflection using the sling with the way I have them setup.

2 of my LE6920 rifles have KAC RAS rails with vert foregrips. Using the fore grip as a barricade stop, I can induce deflection with irons, but again, it takes a lot of force to do it. Standing and shooting using the fore grip as a handstop, I am not able to induce deflection.

In my opinion, I would think using a laser it would be more noticeable in regards to deflection, but then again, how much force does it take to do that? I’m 250 lbs and I really need to lean in to the rifle with the bipods locked into a fixed position to get any type of deflection. The shorter the rail, the more force it will take.

I think davidjinks' input pretty well settles it.

It occurred to me that you'd potentially see more deflection issues if you were propping your exposed barrel on a barricade. If you grab a 16" barrel in a 13-15" FF handguard and torque it, it seems to me that the barrel moves within the HG, while the HG itself remains mostly rigid. I think you can put pressure on your HG with a sling, barricade, or bipod with pretty minimal consequence.

If you're getting into night vision, just friggen get into it, and see what works for you. It's fun to talk about, but only to a certain point.

quote:

Originally posted by KSGM:
He did mention MAWL, so the illuminator is covered.

Good point. I missed that.

I reiterated my experience above originally. I have not a clue what a V7 rail is like and how it attachs. But to be able to tell you are deflecting the rail working with irons means that the movement has to be what 5MOA? 7MOA?. big numbers.
That simply does not even closely mirror my experience using DD or Geissele rails off barricades with serious pressure, forget under night vision and laser aiming but while running optics in daylight. Not a chance my shots are that far off (even accounting for the fact I suck).

quote:

Originally posted by hrcjon:
I reiterated my experience above originally. I have not a clue what a V7 rail is like and how it attachs. But to be able to tell you are deflecting the rail working with irons means that the movement has to be what 5MOA? 7MOA?. big numbers.
That simply does not even closely mirror my experience using DD or Geissele rails off barricades with serious pressure, forget under night vision and laser aiming but while running optics in daylight. Not a chance my shots are that far off (even accounting for the fact I suck).

Rail in question:

https://www.vsevenweaponsystem...ed-keymod-handguard/

Barrel nut:

https://www.vsevenweaponsystem...eplacement-hardware/

Again, I stated in my previous post, it takes a lot of force to cause deflection.

I have used DD RIS series rails as well. And yes, you can cause deflection in those rails as well. It has been documented through Mil testing that it happens. But again, it takes a lot of force to do it.

As another poster mentioned, which I didn’t even touch on, barrel deflection is a thing as well. In my opinion it is easier to cause barrel deflection rather than rail deflection. Hit a barricade, use the barrel as a rest and start cranking down, you’ll see some shift in POI.