Rail mounted iron sights accuracy AR-15

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weirdsexy

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Hey guys,

I posted a thread a few days ago regarding a planned AR build.

I was planning on this upper.

Unfortunately, these uppers are estimated to be out of stock for at least another 8-12 weeks and there's no guarantee of me getting one when they restock.

On the other hand, this upper is in stock right now!

I really didn't want to go shorter than an 18" barrel. But I rarely shoot out any further than 300m so I don't guess it will make too much of a difference (confirm or deny?).

My question is this: In the last thread, people were telling me that if I was planning on using iron sights, the front sight better be mounted on the barrel for accuracy. Is this only because, in theory, rail mounted front sights will move with the free floated handguard? Let's say, in theory, if the rail mounted sights were zero'd in and the handguard didn't move after that, would it be every bit as accurate as a gas block type front sight?

I ask this because, going with the 16" barrel requires the use of a 9" handguard to use a front post sight/railed gas block. I think the 9" guards are awkward and would rather a 12" both ergonomically and aesthetically. As long as accuracy shouldn't suffer too too much with a rail mounted front sight, that's what I'm going to do.

Also, 16" means mid length gas. I'm building with an A2 buttstock. The kit I ordered comes with a standard buffer. Should I order an H buffer to compensate for the shortened gas system?

Thanks guys, let me know if I need to clarify anything.
 
You will not notice a difference between a 16 and 18 inch barrel.

Depending on the rail you can get some Flex and this can lead to a very small POI shift.

And one thing. I would suggest looking at some other rails. Larue does many things right. Rails are not one of them.
 
Rail mounted sights are for backup when your optics fail. In the last thread, people gave you practical advice. Theoretically, you should be fine on a properly installed free float rail that won't rotate or move. Depending on intended use, that's going to require some faith on your part that your build will keep its integrity if you drop it, or if your railed sights get knocked around while you are on the range. Barrel flex is another variable to consider.

Sure, get an H buffer, it helps a lot. Try the Spikes Tactical T2 Heavy Buffer. It's a winner.

http://www.spikestactical.com/new/z/lower-parts-spikes-stt2-heavy-buffer-p-201.html
 
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I'm building with an A2 buttstock. The kit I ordered comes with a standard buffer. Should I order an H buffer to compensate for the shortened gas system?
Click to expand...

A standard rifle buffer is 5.2 OZ which is heavier than an H buffer or the ST-T2.
Rifle buffers and carbine buffers are NOT interchangeable anyway.
 
Okay, what about this Daniel Defense upper group?

Don't get me wrong, I'd rather have the sight base mounted on the barrel, but I'm not willing to sacrifice the 12" handguard to get it.
This rifle will probably get treated very gently, I would hope I'd never drop it.

I mean, I realize it might be less accurate but by an unacceptable amount? I'm no competition shooter.

I'll eventually put some optics on it, but it's fun to be able to use the irons functionally.
 
Sam Cade said:
A standard rifle buffer is 5.2 OZ which is heavier than an H buffer or the ST-T2.
Rifle buffers and carbine buffers are NOT interchangeable anyway.
Click to expand...

Oh, see I'm unfamiliar with the platform. I'm especially unfamiliar with all the adjustable stocks, etc. as I don't care for them. So is there a heavier rifle buffer I should consider purchasing to increase the reliability of cycling/decrease wear on the internals?
 
So is there a heavier rifle buffer I should consider purchasing to increase the reliability of cycling/decrease wear on the internals?
Click to expand...

Standard parts will do just fine. I would assemble the rifle and see how it shoots before I start messing around with the timing.

I mean, I realize it might be less accurate but by an unacceptable amount?
Click to expand...
Depends on the forearm and how hard you are twisting it.
 
Could you specify the target and range you intend to shoot?

Frankly, delving into Brands and what buffer to use is much further down the decision tree than it seems to merit right now. It's preselecting parts before the job is even outlined. There's no way to tell if that part or vendor will even make the short list for the job.

As noted, a choice of buffer needs to compatible with the stock used and buffer tube. Citing alternate carbine buffers to discover a fixed length rifle tube will do a better job is counterproductive.

What range, what target, that fixes caliber and barrel length. Then decide what upper, optics, furniture, and trigger, in that order, support the specific needs of that job, and don't bother trying to consider all the 2% what if scenarios that might come up. They only compromise the gun and make it less than optimum for the 85% of the time it needs to be best.

Don't start drinking the testosterone laced koolaid of Brand fans, and you get what fits the job - not your cash in their wallet for whatever they sell.

PS most scope companies and rail makers do NOT recommend bridging a mount - attaching one ring or end on the upper, and the other on the rail. That's how floppy rail fore ends are considered - up to and including cautions doing so will void the warranty for abuse as it will damage a scope tube. Rail mounted BUIS are for a gun that uses a primary optic on the upper. They are short range backup.
 
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Tirod said:
Could you specify the target and range you intend to shoot?

Frankly, delving into Brands and what buffer to use is much further down the decision tree than it seems to merit right now. It's preselecting parts before the job is even outlined. There's no way to tell if that part or vendor will even make the short list for the job.

As noted, a choice of buffer needs to compatible with the stock used and buffer tube. Citing alternate carbine buffers to discover a fixed length rifle tube will do a better job is counterproductive.

What range, what target, that fixes caliber and barrel length. Then decide what upper, optics, furniture, and trigger, in that order, support the specific needs of that job, and don't bother trying to consider all the 2% what if scenarios that might come up. They only compromise the gun and make it less than optimum for the 85% of the time it needs to be best.

Don't start drinking the testosterone laced koolaid of Brand fans, and you get what fits the job - not your cash in their wallet for whatever they sell.

PS most scope companies and rail makers do NOT recommend bridging a mount - attaching one ring or end on the upper, and the other on the rail. That's how floppy rail fore ends are considered - up to and including cautions doing so will void the warranty for abuse as it will damage a scope tube. Rail mounted BUIS are for a gun that uses a primary optic on the upper. They are short range backup.
Click to expand...
I will most likely be shooting distances =< 300m.
Paper targets or plinking is the main purpose.

What I really want is an upper group with 18" stainless barrel, 12" handguard and a railed gas block. Always out of stock with BCM and no one else has exactly what I'm looking for. So, I'm down to either a 9" handguard with a fixed front post sight or a 12" covering a low profile gas block.

I think I'm just going to go with the 9" and FPS, I'm sure it will grow on me.

Will the front sight get in the way if I put a red dot or holographic sight on in the future?
 
Have you considered mounting a FSP after the handguards? I was looking at that type of setup when I first started looking for an AR, I liked the "dissipator" look. I eventually settled on a conventional mid-length, but its something to think about.
 
CFletch08 said:
Have you considered mounting a FSP after the handguards? I was looking at that type of setup when I first started looking for an AR, I liked the "dissipator" look. I eventually settled on a conventional mid-length, but its something to think about.
Click to expand...
You mean like attaching a FPS after the handguard and not using it as the gas block?
No, I hadn't really thought of that ha.

I'll consider that, but I think it would look odd at the very least.
 
Look up "dissipator" (iirc) on del-ton or model-1 sales websites (some others make em as well). They are odd, but they give you a longer sight raduis and longer handguards.
 
Yep, if the goal is just to have a solid front sight post, you can use one of the cut-out rails with a standard carbine or mid length gas block front sight. If the purpose behind this is to increase your sight radius, you will need to do something like the Dissipator setup... get an extra gas block front sight and install it on the end of your barrel.
 
I can't stand the way those cutout handguards look. I was/am actually considering the dissipator setup but I think I'm just going to go with the standard middy setup 9" guard and FPS.
I think it's going to look weird with an A2 stock, heh.

Oh well, I'm sure I'll be happy with it.
 
I can't stand the way those cutout handguards look. I was/am actually considering the dissipator setup but I think I'm just going to go with the standard middy setup 9" guard and FPS.
I think it's going to look weird with an A2 stock, heh.

Oh well, I'm sure I'll be happy with it.
 
The best thing about the AR-15 is that you can change it down the road if you so desire, so don't be all that stressed about it. You can't choose badly, both setups will serve you well.
 
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