A2 fsp/gas block vs BUIS on free float handguard

[Chriznak]

What are the merits of each of these options and which one do you feel wins? I've read that the A2 front sight post is the more "reliable" option. I've also read that if your barrel does not have the correct dimples then you don't have the "low profile gas block under free float handguard" option.

[EkuJustice]

You always have the low profile gas block under the hand guard option and the dimples help prevent it from moving and are done for the gas block installed. Other options are a clamp on or cutting down the front sight tower. I have run the yhm gas blocks with the set screws and they tent to get a good bite and I have never had one move.

[co-exprs]

+1. It depends upon the mission of the rifle. If you intend to run RDS or magnified optics as primary and irons with only backup intent, then a handguard flip up is clean and easy. If your intention is to run irons at distance then an A2 sight tower is the way to go. The real trade off though is accuracy. The handguard flexes!under use, shifting the POA. You simply dan't count on handguard mounted flip up sights for any sort of precision shooting. On rifles where I mount irons, I do both a low profile gas block and an A2 tower mounted out in front of the longest handguard I can fit. On my LRP-07 I run an 18" barrel with a 15" handguard, low profile gas block and an A2 right at the muzzle. You don't need any dimples as the gas block is easy to align. The A2 is a bit of trial and error.

[MickB]

You can always chop the A2 FSB and make it a low profile gas block that is pinned to the barrel.

Have a FF hand guard cover it and mount you BUIS on the rail....

Mick

[Ragnar]

If the primary purpose is to use irons then a standard FSB is the way to go. I prefer pinned bases but only when done when after assembly and by a competent gunsmith. Nothing worse than having the rear significsntly sight off mechanical center.

Surprisingly the only clamp on FSB I have found is the JP. It is adjustable and pricey. Anyone have a source for a standard clamp on A2 FSB? Seems like a waste to use the JP near the muzzle when not part of the gas system.

Some day I hope Noveske will offer their stainless barrels with seats for a standard FSB.

[co-exprs]

I am a huge fan of JP products and have a JP clamp on FSB on one of my rifles. Recently however I tried the Armalite clamp on unit on my 308. It worked awesome and is considerably cheaper. You know what... when I'm looking through the rear sight, I can't for the life of me tell the difference between the expensive and less expensive units.

http://www.armalite.com/ItemForm.aspx?item=EU0240NMPKIT&Category=07033031-2a2e-439c-a701-edf0d7327c93

Just as a small needling detail. If your intention is to have irons sights on a combat style rifle, which will rarely be shot for precision or past 300yrds, then a pinned FSB is fine. If you want to be able to hit 4moa targets out to 600yrds, then a clamp on FSB is the way to go. The pins are tapered and the pin holes break out the side of the barrel. This turns the tapered pins into wedges. The tighter they fit the more they flex and stress the barrel. Out to 300 you probably won't notice a difference, but at 400 and beyond, you are more likely to struggle with hits on small targets.

[Ragnar]

Thanks for the link co-exprs. I new armalite made them and thought they stopped because I could never find one in stock. Do you have a source for sleeves when the barrel is less than .750?

I agree that taper pins can have an effect but I never found it to be significant enough to worry about when field style shooing with irons. For me, The only real drawback to a pinned FSB is that it is not something that is DIY for the average person.

[co-exprs]

My FSB installations have been on barrels with a barrel diameter of .740" in front of of the gas block area. I just cut two thin strips of .005" shim stock and wrap it around the barrel and then work them into possition. Cheap, works great and you can't seen the shims once installed. I did an installation on a barrel once, with a .725" OD at the muzzle and had to use .012" shim stock. That was much more challenging to work with but I kept at it, till the install was right and it turned out swell, but I'd hate to have to use any shim thicker than .012".

[Lead-Head]

Another option is removing material from the FSB between the bands that clamp down around the barrel. I have done this on both the armalite FSG and the JP with good result.

[Pinecone]

Has anyone tried this:

http://www.holsters.com/competition/accessories/rk-m4-2.asp

I am looking to put angled BUIS for very close range, with a 1-4x for primary.

[LSnSC]

I use a PRI same plane clamp on gas block mounted out behind the comp with a Troy fixed front attached to it. I replaced the front post with a .040 post from White Oak Armory. As posted above, I removed a little material from between the clamps so it locks down tight. Looks kinda funky, but it works really well. The HK globe style ears on the Troy sight give me kind of a circle in a circle sight picture. Up close I can shoot it as fast as a red dot and more precisely than a dot at distance.