mounting question: fixed front sight on FF rail

[Absolvo]

Hi you all,

Long time reader, 2nd time poster. Completely new to AR's. I appreciate any help.

I bought three AR's (go big or...something)
1. colt 6720
2. upper BCM 16" light weight middy with MI ss12g2
3. for my father: upper BCM 16" LW mid with Centurion Arms C4 12"
I'm still waiting on the lowers for the two uppers and using the colt lower in the meantime.

My dilemma is my father just informed me the he wants iron sight only and he expects accuracy (long time rifleman and korea vet.). However, I don't know how to get a front sight mounted on a 12" rail without having the sight move with the FF rail. I looked into buying a fsb and installing it on the front, but that is beyond my skill level, so I would have to pay a gunsmith to do it properly and that is money I'd rather save if possible. I understand the changes in accuracy with a front buis on a FF is relatively inconsequential for combat engagements, but my dad will be a target shooter only and I want him to have a good experience. I've already decided that an LMT A2- style sight will be best for him, but the front sight is beyond me.

1. Can I buy a gasblock or similar that securely mounts to the barrel in front of the rail (no gunsmithing required), then attach a fixed front sight to it?
2. Is there a front sight that mounts to the barrel (aside from a standard fsb)? The barrel doesn't have taper pins and I'm not about to drill into it.

I believe, the barrel diameter is .625, not .750.
If, in your experience, you have found that the decrease in accuracy is hardly perceptible by the common man, then I'll probably go with DD or Troy fixed front.

Thanks,
Dan

[Iraqgunz]

Dan,

Your post doesn't make sense. Can you please clarify? For the record I have a 16" Colt barrel with a copped FSB and a Centurion Arms rail and it is able to do around 2 MOA last I checked.

I'm just confused about what your dilemma is or what you want to accomplish.

[Absolvo]

Dan,

Your post doesn't make sense. Can you please clarify? For the record I have a 16" Colt barrel with a copped FSB and a Centurion Arms rail and it is able to do around 2 MOA last I checked.

I'm just confused about what your dilemma is or what you want to accomplish.

Sure,
In short, I'm worried about iron sight accuracy on a 12" ff rail because the sight will move (to some degree) with rail. I'm concerned that would be frustrating if my father was shooting from a bench rest or whatever and putting pressure on the rail. I've read the post concerning FF rails and buis, but these sight won't be backups. It's all he'll use, so I just wanted to give him the best chance for accuracy (probably not past 300 yards, but he's a surprisingly good shot). If he was using an optic, I wouldn't be concerned. Does that make sense? In hindsight, I think I would have bought a model with an FSB for him, but he didn't tell me what kind of setup he was looking for until today.

2 moa is great. Can I ask what range that was out to and sights you were using? Thanks.

[grunz]

Good Rails properly installed are surprisingly stiff - I wouldn't worry too much about it.

[Absolvo]

Good Rails properly installed are surprisingly stiff - I wouldn't worry too much about it.

good. I was hoping this was the case. Both the C4 and the MI g2ss seem like top notch rails. I'm sure it will be fine. The main thing just get it to him and let him shoot it! Thanks for the feedback fellas.

[Iraqgunz]

When speaking in MOA it generally implies 1 inch at 100 yards. So in this case it was 100 yards well. I was using a troy front sight and a KAC 2-600 meter rear sight.


Sure,
In short, I'm worried about iron sight accuracy on a 12" ff rail because the sight will move (to some degree) with rail. I'm concerned that would be frustrating if my father was shooting from a bench rest or whatever and putting pressure on the rail. I've read the post concerning FF rails and buis, but these sight won't be backups. It's all he'll use, so I just wanted to give him the best chance for accuracy (probably not past 300 yards, but he's a surprisingly good shot). If he was using an optic, I wouldn't be concerned. Does that make sense? In hindsight, I think I would have bought a model with an FSB for him, but he didn't tell me what kind of setup he was looking for until today.

2 moa is great. Can I ask what range that was out to and sights you were using? Thanks.

[markm]

I've experienced what you're talking about a little bit. I'm not sure if it's an issue of an odd ball sight radius or if it's all mental...

But I don't shoot my Fixed Iron on my 12.0 as well as real irons. I just try not to push the receiver group in any way that would cause the barrel to dive inside the rail.

[Blowby]

The closer he rests the AR onto the (insert object here) in relation to the upper receiver the less leverage you will have working against you. You should be fine.

[Absolvo]

This is all good info. Thanks. I think I'll go with lmt rear and Troy fixed front.

[The_Hammer_Man]

The MI SSg2 tube is a rock. IF it's properly installed it will not move a millimeter... even during mag hammers.

I set up an upper for a client with the 15" SS g2 tube and mounted KAC flip sights on it. 2moa groups with 55gr FMJ and sub moa groups with 77gr SMK is definitely doable.

Granted, there are a ton of other variables such as trigger pull weight and type (single or two stage), barrel length/twist rate (customer barrel was a WOA 18" 1:8 w/ a Levang comp).

But, in general, if your tube has been installed correctly and you have a decent quality barrel you should be able to hold 1 moa all day with fixed sights.

YMMV of course.

[markm]

But, in general, if your tube has been installed correctly and you have a decent quality barrel you should be able to hold 1 moa all day with fixed sights.

It's not about the strength of the rail... or "tube". It's about how much the barrel can drift in the rail with receiver flex, etc.

You can pic up about any FF AR15 and grab the muzzle and flex the barrel/receiver from the front of the gun.