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Folks, I bought a set of A.R.M.S. inc. flip up sights. (they weren't cheap). I had planned to mount them on my S&W M&P15 ORC. I have some optics choices but I wanted to set up iron sights to practice shooting w/o optics @ 25 - 50 meters, and have a back up if the optic fails. On the box though, it's printed "Do not mount on Dovetail Gas Blocks". Will I melt and ruin the front sight if I use it?

I also have a detachable steel front sight and detachable carry handle rear sight, but that won't allow me to use the optics.

Advice will be appreciated...

If you have a A2 standard front sight, you can mount a rear flip up sight and an optic, and the front sight won't bother you one bit.

I submit the carbine I built for my wife as an example:


That rear sight is an A.R.M.S. #40 L-P. The front sight is a standard A2 front mounted on a M4 profile barrel.

All of this said, unless the front sight you bought is plastic, It seems to me that a metal flip up front sight wouldn't be that affected on a rail type gas block. After all, the A2 front sight is mounted on the gas block.

Could be a sight height problem. I believe you need a front sight specifically engineered to sit on a gas block picatinny rail (as opposed to a full length handguard/quad rail set up)

A-R wrote:Could be a sight height problem. I believe you need a front sight specifically engineered to sit on a gas block picatinny rail (as opposed to a full length handguard/quad rail set up)

That's true, and that could have been the reason for the warning. If the rail on the gas block doesn't mount the sight at the same height as it would be mounted on a forward rail, then your elevation adjustments will be useless.

Perhaps a simpler solution, although more expensive, would be to ditch the gas block for a low-profile one, and then mount a floating quad rail. Put the front sight on the quad rail. You'll also free up a little more accuracy in your rifle that way.

Thanks for the replies, and that's a nice looking carbine there, AM. I'll see if a picture would help... I suppose I could use my steel front sight and polymer rear flip up sight. Just seems like the wrong way to set it up.

I thought I read somewhere never to mount a sight on a handrail. Is that not true?

sight on the handguard can be iffy in theory. If you think about a floating barrel and having a sight mounted on something else you maybe could have an issue. If you look at an MP5 the front sight (tripple tree) is mounted to the barrel and the forearm connects to the cocking tube, not the barrel. The cocking tube floats inside the triple tree. On an AR with a rail forearm I don't see it being an issue. Besides I would only use the "irons" on my m4 if the eotech died.

JeepGuy79 wrote:sight on the handguard can be iffy in theory. If you think about a floating barrel and having a sight mounted on something else you maybe could have an issue. If you look at an MP5 the front sight (tripple tree) is mounted to the barrel and the forearm connects to the cocking tube, not the barrel. The cocking tube floats inside the triple tree. On an AR with a rail forearm I don't see it being an issue. Besides I would only use the "irons" on my m4 if the eotech died.

Not familiar with a "cocking tube". I believe the issue with a polymer front sight on the gas block is heat not height. The newer Smith & Wessons have a gas block that is the same height as the reciever.

sorry, it is the thing right above the barrel on an mpo5. I was just referencing it to show how they intentionally floated the barrel and put the sight directly on the barrel.

igotta40....Give us the A.R.M.S product number. I have never seen a polymer front sight. Belay that....leave it to A.R.M.S. You must have a #71L-F. And yes, the problem is the difference between heights of barrel mounted, and handguard mounted sights - plus the stupid polymer.

IIRC "dovetail" sights are taller and align with the rear sight. They cannot be mounted on a handguard rail because they would be too high. The little illustration on the right shows this difference:

http://www.castlerocktactical.com/sights.htm

On the left edge of the picture you can see the rail atop the handguard and how much it is offset. The bad news is you must mount the #71L-F on a handguard. I would look here for some sights that work. I've used YHM for years and they are first class. Much better than A.R.M.S. stuff IMHO.

http://yhm.net/?zenid=608029f0253949f3604b7241d1d30ed6

And by the way...it doesn't matter where the sights are mounted as long as the rifle shoots to point of aim and there is sufficient adjustment to allow for loads that shoot to different points of aim. The only issue is movement.