Hi all,
Handguards that provide a continuous top rail are popular these days. But I am wondering… if it is not recommended that you mount optics across the gap between the rail and receiver, what’s the real benefit? Is the fact you have a couple extra rail section really important, vs. say, the Larue rail?
Also, as a side question… is there any problem with mounting a red dot optic on the railed handguard instead of the receiver?
Thanks for your time and insights.
Chris
Its not a big deal to me but may be to others. I see the benefit in a monolithic design which would make scope mounting a little easier but a bolt on rail doesn’t have the same rigidity. Even then Id still keep the optic mounted as close to a normal position as possible. With cantilever mounts Ive never found a need to mount an optic further forward than a standard receiver allows anyways.
As far as mounting optics on the rail the rail is subject to flex and just 1 degree of movement can cause a POI shift of over 60" just at 100 yards. I don’t think it would be that hard to get a rail to flex 1 degree just through normal use like using a sling, a tight grip on the rail, using a barricade for support, ect. Even just half of one degree would still cause a major POI shift.
It really doesn’t matter much if it’s continuous or not imo, but there is one nice aspect to it, when installing your rail you can clamp a light/scope mount bridging the small gap between the rail and upper as you tighten down the rail, ensuring perfect alignment.
Bridge the gap on a non-monolithic top rail? With a solid 1-piece scope mount maybe but don’t do that if you’re using 2 separate rings.
I used to run my optic on my rail, just forward of the reciever…that was on my shorty though.
I still run it a little forward but I have a cantilever mount now
Should have been more clear, I meant it is a possibility with the monolithic, not with the gap type. Something like a Larue or Bobro 1 piece may be able to do it over a large gap, still better on a monolithic setup.
He was referring to doing it temporarily, during the rail installation process, as a jig to keep the rail aligned with the receiver.
Chris,
I understand your question because I had/have the same one. Basically, it all kinda depends on how much shit you “need” to attach to your rifle. Military and S.W.A.T end users may have requirements that demand every inch of rail space they can get. A Mono upper does give you the most flexibility in the location of your accessories.
Downside, as I see it, is that it also adds weight. I have a light, sling mount, and an AFG on my fore end. That’s it. So I went with the MOE hand guard. I only have the rails I absolutely need and they weigh a lot less. I’m still evaluating this set up, but so far I like it. I could just as easily gone with a DD Omega rail. Well, maybe not that easy. There’s a $200 price difference. But that’s besides the point. I should also add that my rifle was configured with lightweight being top of the list. So a Mono rail system would have added a “lot” of weight with zero benifit for my uses.
And then there are some who will get them cuz they look cool. And I agree, they do. I just don’t need all that rail space.
For a short time some mono rails were advertised as giving you the benifit of being able to span your optic past the edge of the receiver. Now that we know that’s not a great idea, the only real benefit I see is more rail space and flexibility in where your accessories get attached.
Hope that helps and hope I didn’t step on the toes of anyone with a Mono setup. Didn’t mean to, these stups are great. I was just pointing out what I see as the pros/cons/reasons. Correct me if I’m wrong.
Ah ok, gotcha.
Good idea for installation but still doesn’t account for flex that might happen when using a tight sling or something.
Hey now, “because it looks cool” is a totally legitimate reason to buy expensive things for your rifle in my book. 
I know I do it.
(1) Red dot placed forward on rail, better accuracy.
(2) Restricts movements between handguard and upper assembly, better accuracy.
(3) Less parts (mono), simplicity.
Amazingly, every single one of your points is wrong. That is impressive. Let’s examine why:
Placing a red dot on a rail is detrimental to accuracy. Even a minimal amount of flex can cause huge POI changes. Even if this wasn’t the case, the forward or rearward placement of a RDS is unrelated to inherent accuracy potential.
The fact that a forearm rail appears to connect with the rail on the upper receiver does not restrict movement. There are plenty of rails out there that do not present a monolithic appearance, yet still have extremely effective anti-rotation mechanisms. Even if they didn’t, since we’re talking FF rails, and since you now know not to place optics on rails, accuracy is not a factor here.
Rails that appear to connect with the upper receiver are not monolithic and do not have less parts. It’s just a matter of appearance.
BTW I’m not saying I don’t like continuous top rails. I use the DD Lite Rail on many of my rifles. But your reasoning is false on this.
Post because you have something to say, not because you have to say something.
+1
IMHO, unless people are running NV in front of RDS, I’m not sure there is a good reason for a continuous top rail.
FWIW I do use a continuous top rail. KAC URX II. One day maybe URX III.
I believe he was referring to a mono upper like an MRP or Vis. In which case mounting a RDS further up past where the conventional upper receiver ends would be fine.
EDIT Although mounting further up in not for me particularly I can see how it may aid some situational awareness for some users.
On another note… I find it odd that on the DD website they show an Eotech mounted on the RISII rail itself and not even spanning the upper+rail. Idk how comfortable id feel with that set up.
While I can agree with this, its to an extent.
I had my optic on the rail, I prefer it forward.
Flex does affect accuracy…if youre shooting long distance.
With an SBR, using it for work UNDER 100 yds it doesnt affect it to the point of a miss.
You might not get groups under a 1/2 inch but it works.
Running something like a M2 or T-1 with a 4moa dot, in a CQB scenario, it will be fine on a rail
Persons above pretty well address my replies. And as far as point (1) goes, I’m not talking about placing it above the bbl or anything, just a touch more forward on the upper. I agree with (2) in that there are rails with very nice anti-rotation mechanisms. I run all LaRue, DD would be a nice choice too. Vis and MRP is what I had in mind for (3). From memory, MRP has 13 less parts…they use that point to promote their upper. Anyways, back to browsing the forum…
Alright. The OP wasn’t talking about monolithic upper receivers. So that’s why your reply seemed off. In the context of actual monolithic uppers, some of your points are valid.
I see. I missed the latter portion of the OP in part.
The continuous rail has the advantage of giving you some more space for your scope mount. (I assume we’re talking more like an SPR type setup) Some mounts don’t give you space to run BUIS as well. So in that regard, it would have benefit. If you use a LaRue SPR mount for your scope or run a red dot, there is really no huge advantage over a quality rail system.