My pleasure.  I am going to try and sell some stuff on EE to get some cash together for another CA upper and/or some optics.

On a different note, I intend to nerd out on POU and manual of arms considerations at some point, in order to demonstrate why I build my rifles the way I do.  I am always very interested to hear others thoughts on those subjects as well.

I'm working on something. When I get my barrel work done, I'll post up some pics.

I'd be interested in hearing. I'm 50/50 on FSB and flip ups myself, there's an application for both IMO.

Looking forward to this. Your modified 9" DDM4 rail is my favorite in the thread (been scanning the EE for one to attempt myself). Will be a tough act to follow!

Also interested in your perpective. FSB builds work just as good for me as my flip builds... just as long as the forend is midlength or longer (Sasquatch arms).

Ideally I would like to post pictures to specifically describe what I am referring to, but in a nutshell I will attempt to do that here:

There are lots of different ways to skin a cat; one's manual of arms preferences usually come about due to some combination of formal training, references, first-hand experience and ongoing adaptation driven by requirements (real or perceived).  Manual of arms drives how a rifle gets set-up and what goes on it.  Adavances in technology, new experiences and new requirements (real or perceived) lead to new things being put onto a rifle, which in turn affects one's manual of arms.  It has been a cycle of ongoing change and I have been riding it for ten years.  In that time I have tried a cornucopia of devices and techniques which, for me, have boiled down to the following "requirements" (real or perceived):

(1) Carbine.  16" or 14.5"
(2) Variable power optic.  1-something, durable, low-light illumination and a bold daytime reticle
(3) Iron sights.  However, not for the reason many keep iron sights on a rifle.  I want iron sights on a rifle because I enjoy shooting them, I am good with them and I see them as a perishable skill that is worth knowing.  For example, should I one day find myself holding a rifle with iron sights in a bad situation, I feel confident that I can use that rifle effectively because I shoot the sights often.  The same cannot necessarily be said about a person who shoots optics exclusively. I even keep fixed iron sights on my rifle at work because I am so comfortable with them (see next item on this list for a caveat).  Now, on my own rifles I do use optics as previously indicated.  I keep a larue LT103 w/CSAT aperture on the rifle under the rail.  My "perceived" reason for this is as a backup iron sight.  My "real" reason for this is for fun, because I don't really think I need backup iron sights.  Optics are rugged/reliable these days and very unlikely to fail.  I keep the LT103 on the rifle because I actually do most of my shooting with it.  At the end of a range session, it goes back under the rifle and I confirm zero with the optic again.  This probably seems silly to a lot of people but it satisfies my needs, both real and perceived, perfectly.  Finally, I believe in a pinned, free floated front sight base.  This is opposed to one that is bolted onto a FF handgaurd and therefore moves independently of the barrel.
(4) Weapon light.  A must have on a defensive carbine for more reasons than I care to elaborate here.  Also, ultra important for a gun with iron sights.  
(5) FSP cutout rail.  I don't just have them because they are sexy. I have them because my hand placement has some slight overlap with the gas block.  Furthermore I like keeping the weapon light forward to reduce shadow.   Finally, hot barrels and barricades.  

ETA (6) Sealed-bottom muzzle device.  Because prone dust signatures in the day are as dangerous as flash at night.

There's more, expecially when it comes to my shooting positions and how this set-up nests with them for me.  However that is for another time, with pictures.

What is a pinned, free floated front sight base?

That's my overly wordy jargon for a plain old fixed M16/M4 style gas block/front sight base.  When I call it pinned, I am referring to the taper pins that are used to secure it to the barrel.  Now, by free-floated, I mean I remove the handguard end cap so in addition to having the barrel floating, the front sight base/gas block is too.  The free-floating FSB is just a pleasant consequence of free-floating the barrel.  Which is the case for every build shown in this thread.

Troy calls this rail a free float drop in, but I don't look at this as a true free float. I am posting it anyway because I really love this setup.  Just a PSA Premium M4 with a few things added/changed.

That particular fixed FSB BCM is my wife's, which she used to shoot all the time. She has since moved on to a 10.5 PSA CHF upper that she now uses for her HD gun. I also have a standard 6920 that I'm getting ready to have the barrel chopped and will probably go with a C4 carbine cutout rail, but that's gonna be down the road a little.

Love it. One observation, and by no means trying to be an internet commando dick: unless you use the front sling swivel, I would remove it to eliminate any rattle between it and the rail. Just my two cents. Your opinion may differ.

Well done.

Awww FSB thread!! Always wanted one and an OTAL just 'cuz... Finally came to just a couple months ago!



14.5" pinned with 9" DD rail.

You win the day, my friend. Big fan of the DDM4 rail. You've also confirmed my suspicion... the 9" is a perfect fit for a midlength fsb. Well done.

My A4-ish Modern A1 build:

Centurion C4 12" rail
Brownells 20" 1/12 A1-type blemish barrel
A1 flash hider
Slickside upper
Chrome bolt carrier (no fwd assist serrations)
A1 stock w/ A2 buttplate
A1 grip
Range Tool lower w/ PSA LPK

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(Ejection port cover spring flipped under while putting on the handguard)

Was gonna buy an ACOG at the end of the month but the water heater went out yesterday.



With optic - Burris AR-332 w/ pic rails removed and screw holes filled w/ JB Weld and a GDI R-Com E-model mount.

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You don't really NEED water, an ACOG is a necessity however

12.5 with AEM5 suppressor and brake collar system. Rail is KAC carbine FF RAS.

Didn't think about the SIR being free float, but it is.
11.5" HBAR 1/7 with SpecWar

10.5" LMT

Very nice. Love everything, but the rail flag (remove to go full stealth ninja... relocate to Battle Mug for Garrison use only... haha). I kid. Well done.

Straight out of James Cameron's Aliens. +1 for a unique interpretation. Very cool.

Edit: Double Tap-Tap-Taparoo.

I don't know... looks like a RAS or RIS... I am questioning the free-floatyness. You win some points back for the OTAL, though. Looks good.

It's a KAC RAS II.  It's a free float handguard.

Holy toshitos, you're right. I guess the arm was camoflaged by the optic for me. I stand corrected.

@edwin907

You are cool, once again.

Bump it up... We need some more pics, people. Keep the dream alive.

Love the DD FSP rails. Very nice. How do you activate your light with you AFG2 all the way back by receiver? Just curious if you have a pressure pad hiding somewhere.

Yes, it's wedged between the top and left side rails.  All I have to do is press it with my thumb.

I figured. If not, my next guess would have been that you were a lefty with two different support grip positions! Your solution is the logical one.

Where did all the builds go? I have a few minor changes in the works on my rifle in post #1. Should have some pics over the next few weeks.

Shot a 480/500-20x in the walk-and-paste match, then followed with a 6.5 MOA group for the SHTF challenge.

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I'm so excited, and I just can't hide it...

Geissele MK8 13 with DIY carbine FSB cutout.

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This one took a little work because of the way the rail installs.

On the rail, I cut out the top area, the bottom ribs near the front taper pin hole and made the distance between anti-rotation tabs wider. I had to remove the ribs by the front taper pin to be able to insert and remove the pin. I had to make the distance between anti-rotation tabs wider so I could rotate the rail further, again to be able to insert the taper pins. I also had to remove the C clip from the ejection port cover rod to slide it back some as it was also keeping the rail from rotating. If you use 2 set screws on the bottom instead of taper pins, you wouldn't have to do the last two mods.

On the FSB, I removed the bayonet lug and sling swivel. I don't know if you could do this with a clamp on FSB.

Installing the gas tube was interesting. I had to hold the FSB in the cutout with the gas tube inside the rail while I installed the roll pin.

Lastly, I installed the taper pins with the muzzle on a rest and a Geissele Super Reaction Rod in the upper on a rest.

You can do this mod on a MK8 and MK4 with a carbine FSB, MK8 and MK4 13 with carbine FSB or on a MK8 and MK4 15 with a carbine, mid-length or rifle FSB. To use a FSB with taper pins you must use a set screw anti-rotation tab version since the rail must rotate.

I did this all with a Dremel and hand file.

You, Sir, are my hero. Absolutely beautiful. Between this and your DDM4 9 mod, you are inspiring me to take the creativity to the next level. Well done! You win the day.

Where there's a will, there's a way. If you study pics of a rail and know how it installs, you can figure out if it's a possible FSP rail.

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Same rail (Noveske NSR-11)
Different barrels.  My friend's PWS factory SBR lower is in the first picture, and my Noveske SBR in the 2nd.  I decided to redo the upper with a KAC SR-15 M4 barrel and run it as a title 1 firearm.  The SR-15 M4 barrel was cut to 14.5 and the brake was pinned and welded.

Mk4 9.5. I cut it with my dremel then cleaned it up on my buddy's mill.

Planning on going with a 12" barrel and a PRI front sight. Don't know who's barrel I'm going to use yet. Attached File


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I posted this in the MK18 thread a while ago but forgot about this thread.  Here is a pic of a RIS II FSP that I cut to a mock MK18 FSB rail.  Here's to keeping the dream alive!

My Dremel and file handywork:

Very nice. Can you post a few close-ups around the fsb to show the cuts?

I love an FSB.



















And a work in progress:

Now this is what I am talking about. Very nice, my friend. You've got balls. Still working up to my first mod build.

It's only money. 

Measure twice, cut once, and you can't go wrong.

Got an ACOG TA11 to replace the Aimpoint PRO. 

Very cool.

Not sure why, but I feel like we've been on page 4 forever.

This guy

Love it.

Cant believe Im just now finding this thread. Probably because Inhavent been on ARFCOM in at least a year. I returned to buy some parts for this build.

Insearch High and low for pictures if the CMR middy fsp rail and I have only found about three photos. I come in here and someone else is building almost the same rifle I am.

My 14.7 barrel should be here Monday.
This will be wearing a surefire socom series muzzle devise and a Warden.