New Rainier Arms RA-308 Rifle

@JNZ That's Steve Coulston, former Navy SWCC.

The optic can be mounted on the rail just like that if it is a properly installed free-float rail.

@Arc Lol, well, if he was once in the Navy!! I swear, sometimes the Internet thinks that being SF makes you a genius. It doesn't. You may be good at your job, but not even 1/1000th of that job is setting up a carbine. I've met SF guys who aren't really excellent shooters, and that's pretty common because they do a lot of things besides shoot. If I need someone to run a PT course at 3am, I'll get a SF guy. If I need a carbine set up, I'll go to an armorer who knows their stuff.

No. If we're talking a standard upper and barrel nut attached rail, a single mount should never span the two rails. Not Ever. I don't care who's rail it is. This is not even a sort-of-ok-sometimes-if-it's-"properly"-installed issue. It's just no, you don't do that.

Things like LaRue's special upper, Mega's multpart attached upper/rail, Vltor VIS, Seekins has a model, etc all fine and good to go. This.... No.

That is Fortis's Switchrail, so I'm seeing even more Nope than a very tightly locked down, shimmed, and happens-to-be-mate-up-to-rail-spec rail. This is swappable rail system which by it's entire function must have extra tolerance than other designs.

You "can" span the gap obviously, but zero is not going to be repeatable, and I would expect huge shifts over temperature, unwelcome stress in the optic's mount. The bigger joke here is that three of the four groups I've trained with in carbine, can't mount their optics back far enough. I said before that's a preference thing sort-of, but two or three rail spaces forward is pointless if you have to make the compromise to split the gap.

This is just a bad practice, which makes it a bad photo. If this was an optic that wouldn't fit without spanning the gap, well, that's what cantilevered based are for, but this is a photo with infinite rail space. The optic would literally be better off on the handguard alone, AK style.

@JNZ From what I understand, and from personal experience, moving the optic forward allows you to see through the sight better with both eyes open. By that I mean, when the optic is placed in a forward position the different images your two eyes get allows you to better see through the frame of the optic. You result may very, but I've found this help me out quite a bit.

@JohnnyBGood Mounting to the rear as much as possible gives you more field of view. Your head doesn't need to be in just the right spot to see the dot. With both eyes open you aren't looking down a tube at all, your entire vision supports the dot at any point (practically, if the rifle is on target and your head is close). Mounting rearward buys you FOV, it costs you.... Well, I've never actually seen any disadvantage to it.

If it were possible, and someday it will be, I'd put dot on a contact right on my eyeball. In the meantime, backwards as much as possible is the most lenient for cheek weld, moving, and removes the "tube effect".

All the same, I don't care where the optic is mounted, if you like it forward, do that. But the topic at hand here is the an optic mount should never span the gap on a barrel nut mounted rail on the AR15.

@ Yea, even on the rails/riser that connects to the upper, like the PRI specifically, you're then attaching the optic to just that. Designed for it.

@JNZ Maybe this isn't reflected by other people, but when I bring the optic rearward I begin to pick up more of the frame which blocks my FOV. I believe that comes down to how well one's eye's can cross (mine don't at all). With magnified optics it's more complicated because moving rearward will give you more magnified FOV, but can lead to less total FOV. That couples with eye relief is the reason I run magnified optic more rearward compared to my micros which I often run as far forward as possible; which, for me, doesn't block hardly any of my FOV. My conclusion is this might be more subjective after all than previously speculated.

As for spanning the two, obviously horrible practice. What probably happened was they threw the gun together for the photo shoot and a day of some shooting. You won't shoot moa consistently (if at all) with a mount setup like that but you can shoot minute of bad guy or steel plate. That's most likely what's going on here. Doesn't make it right, but it is what it is. Plus, to be fair, the topic was only one sentence in the comment I was responding to making it hardly the "topic at hand."

@JNZ I kind of thought field of view doesn't really matter on a quality red dot. They are meant to shoot with both eyes open - your field of view should be fairly normal, and the dot will just kind of hang out in front regardless of the size of the tube or variance of front-back. There really is no eye relief issue on an RDS. They're not meant to be used as a scope, where your field of view would then become an issue to be concerned with.

That said - it does seem that putting it across the receiver and rail would be unwise, but more from a durability/retaining zero perspective than a usability perspective. Perhaps the rifle balances well with it at that spot because they're using one of those huge, heavy, expensive X10 magazines.

@Mahler You don't need it.... Until you do ;)

@JNZ "Hey, this round's not going in, I'm sure the best course of action is to cram it in! Screw ejecting it and loading the next round in the magazine, I'm sure it won't get stuck in the chamber and need to be prodded out with a stick when the rim rips off." said no one with a brain, ever.