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Posted: 9/11/2003 7:29:17 AM EDT
[Last Edit: 12/29/2003 9:27:35 AM EDT by M4-guy]
This is what happens when you don't do your homework, but I'm hoping the resident experts here can help me salvage this project.  My initial idea was to build a low cost scoped plinker for my postban lower.

Here were the ingredients, some of which I already had:

Bushy 16" bbl w/bare muzzle and milled front sight base
Midlength FIRSH
Generic flat top upper receiver
Armalite 1-piece scope base
Leupold VX-II 3-9x40
Versapod rail adapter and bipod.

After obtaining most the components (I love the EE!), it became obvious that the FIRSH does not completely cover the gas block, which was one my objectives.  The FIRSH ends right between the two holes for the front sight base pins.

As I sat in disappointment and stared at the incomplete upper, a thought came to me (this is the dangerous part).  If I used a full sight base, and aligned the rear pin hole on the base with the front pin hole in the barrel, the FIRSH would fit behind the front sight almost perfectly, with just a small gap between them.  Then the cogs really started turning.  What if I cut my gas block in half (!!!) and used the rear half under the FIRSH for the gas system?  The next problem was the (full) front sight base; it would have just a single pin to fasten it to the barrel.  Would this be enough?  Remember this is just a range gun, and won't be subjected to any rough handling.  Though I could ask my buddy to drill a hole for the second pin.  The front sight would also oblige me to add a folding rear site, which may not be compatible with scope I had in mind.

Or should I just trade my midlength FIRSH for the rifle version, and forget about the front sight?

Any thoughts and suggestions are appreciated.
Link Posted: 9/11/2003 8:20:57 AM EDT
Isn't this fun?

I'm not quite sure what your objective is. I believe it was to have not front sight and have the FIRSH cover the gas block area. If this is the case then you could still just chop off the top of the sight and leave half of it hanging out. No need to exchange or buy anything else. A more secure option might be to just cut out the portion of the front sight that hits the FIRSH. This way they are held together at the bottom.

Personally I like to have all my weapons field functional not just range functional. So I opped for doing something solid whatever it is. I recently put together a 16"car with a car length Firsh and a flip front sight. I liked the clean look of covering the sight base completely with the firsh and mounting a front sight on it. But then I decided that it would be better for my BUIS to be independant of the FIRSH and all other added components to the rifle. I beleive the shorter FIRSH will also hold up better to abuse simply because there would be less to knock around and less leverage for everything to push on. I mount my eotech/scope combinations on the upper and firsh. The FIRSH has put up with all the intentional abuse I put it through and still retains sight zero.

Just some ideas.
Link Posted: 9/11/2003 8:30:52 AM EDT
I'm not exactly sure what I would do.

It sounds like maybe you should get the standard length FIRSH.

A couple of questions though, are you using a barrel with a standard carbine gas port or with a mid length gas port?  (sounds like standard carbine from your description)  I know bushy doen't make a midlength, but you could have had it modified.

Does the milled front site base/gas block fit inside the inside diameter of the FIRSH with clearance?

So basically the end of the FIRSH is at the middle of the gas block?  It fits, just hangs out more than you want?

Link Posted: 9/11/2003 8:33:08 AM EDT
[Last Edit: 9/11/2003 8:33:36 AM EDT by Vector_Joe]
The only thing about getting the rifle length FIRSH is that it is going to be 4 inches longer than what you have now.

From Triple Break Products
F8R  Carbine length    7.125"  10.5  12  $99.00
F85R  Mid length       8.625"  12.5  16  $124.00
F7R  Rifle length      12.55"  18.0  24  $124.00
View Quote
Link Posted: 9/11/2003 10:53:56 AM EDT
Thanks for the input guys.  The initial objective was to have the FIRSH completely cover the gas block.  This was to be a scope-only gun, so no irons were in my plans.  But then I saw that keeping the front sight was do-able, and actually looked pretty good - to me.  (All the pics of members' midlengths must be influencing me subconsciously.)

Good point about keeping everything solid.  Now that you've mentioned it, using one pin to secure the front sight does sound mickey mouse.  On the other hand I'm certainly no operator (the range IS my field [:D]).  Nonethless, if I decide to go this route I'll be sure to have another hole drilled.

As it is now, I would have to completely remove the "hypotenuse" side of the front sight to mount both it and the FIRSH.  This may prove to be impossible, since there would be no way to drive the rear pin in with the FIRSH in place.

Sorry I didn't say so, but the barrel uses a standard carbine gas port.  I possibly would be making a barrel with a midlength sight radius (almost), and a standard carbine gas system - a CAR/Midlength Hybrid, if you will.  "CMH", that's what I'll call it!  You heard it here first!

Does the milled front sight base/gas block fit inside the inside diameter of the FIRSH with clearance?
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So basically the end of the FIRSH is at the middle of the gas block? It fits, just hangs out more than you want?
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The only thing about getting the rifle length FIRSH is that it is going to be 4 inches longer than what you have now.
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The main reason I wanted the midlength FIRSH was aesthetics.  I wanted something different that I hadn't seen before (now I know why!).  But if I can't find a workable solution, and one that's not ugly, this will be the last option.

The part I'm still unsure about working is the halved gas block.  Shouldn't I be able to chop it anywhere in front of the gas tube pin hole?  I'm sure a single taper pin is enough to secure this "semi-block" to the barrel and safely contain the gas pressure, right?
Link Posted: 9/11/2003 11:00:31 AM EDT
We used a half base gasblock on a 4" PDW - it ran 300+ rds C77 ball no problem with a suppressor....

My guess it would be more than strong enough for your usage.
Link Posted: 9/11/2003 6:14:56 PM EDT

How about taking an Oly F7R (rifle length FIRSH) and shortening it?  I planned on doing the same thing you did, but noticed the problem with the mid-length FIRSH after taking a few measurements.  It seems cutting the F7R off between the 3rd and 4th 'long' slot (when you look at it, it's obvious where to cut) would be a near perfect length.  I have yet to try this (didn't want to risk too expensive a part) but I did shorten a cheap free float tube (knurled rifle length) and it worked very well.  I'm considering milling some cooling slots and coating the el-cheapo FF tube with truck bed-liner.  Might actually turn out cool...

Link Posted: 9/11/2003 7:40:45 PM EDT
I still fail to see why a carbine FIRSH would not have been just as good.  Or get a rifle length FIRSH and cut it down...

If your gonna do a full front sight just get the carbine FIRSH and do it right.
Link Posted: 9/11/2003 7:46:01 PM EDT
I got a Med/long FFRAS cut to accomodate my Front sight gas block on a midlength carbine of mine.

 It is doable, I must admit I had an armourer at work do it, and he did a great job.

I ended up like ears around the FSGB - exactly what I wanted.

Link Posted: 9/12/2003 3:51:33 AM EDT
I did the exact same thing a few months ago.  I used a Smith enterprises aluminum gas block cut in half.  Then I cut the second notch in the barrel with a neddel file.  It does not have to be a hole.  I hade no way of drilling a hole on the curved edge of the barrel so I just filed a notch working slowly untill the taper pin would pass through.  Another cool part is that the bayonet now fits.
Link Posted: 9/12/2003 3:55:19 AM EDT
Originally Posted By KevinB:
I got a Med/long FFRAS cut to accomodate my Front sight gas block on a midlength carbine of mine.

I ended up like ears around the FSGB - exactly what I wanted.

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Pics man, pics [:D]
Link Posted: 9/12/2003 6:48:20 AM EDT
I just wanted to add this pic from the OLY catalog for reference:

Link Posted: 9/12/2003 8:41:00 AM EDT
Thanks to the others for chiming in.  Just to clarify/summarize, this was supposed to be a simple project to basically replace my existing front site base with a milled one (gas block), and install the midlength FIRSH over it.  Unfortunately, the FIRSH leaves about half of the gas block exposed, which to me was unacceptable.

I think the decision boils down to whether or not I want to keep the front sight.  And since a scope will be on the flat top, this will depend on if a rear sight will fit behind the scope.  I think I'll wait for my scope to arrive before doing any permanent mods.  But the more I look at the front site installed in the forward position, the more it appeals to me.  It gives the rifle a whole new profile.

inkaybee, it's good to know this has been done before.  Do you have any pics?
Link Posted: 9/12/2003 8:52:25 AM EDT
You shouod be able to fit the KAC 600m sight under the scope in all likelyhood.
Link Posted: 9/12/2003 11:52:46 AM EDT
Originally Posted By Lumpy196:
Originally Posted By KevinB:
I got a Med/long FFRAS cut to accomodate my Front sight gas block on a midlength carbine of mine.

I ended up like ears around the FSGB - exactly what I wanted.

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Pics man, pics [:D]
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I still have not fully assembled it - I guess you have given me something to do now.

Link Posted: 9/12/2003 12:36:40 PM EDT
Cant wait Kevin.  Exactly what Ive been thinking about doing.
Link Posted: 9/12/2003 2:31:54 PM EDT

Originally Posted By KevinB:
I got a Med/long FFRAS cut to accomodate my Front sight gas block on a midlength carbine of mine.

I ended up like ears around the FSGB - exactly what I wanted.

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That sounds like my Danial Defense 9.5FSP.  It is a mid lenght FF rail with a cut out on top for the 16" Sight base.  I put on  PRI and the forend wraps nicely around it.
Link Posted: 9/13/2003 10:08:26 AM EDT
I finally learned how to post pics!
The unfinish project, awaiting optics:


Link Posted: 9/13/2003 11:05:59 AM EDT
That looks real nice.  It balances well with the A2 stock.  Sorry I don't have my digital camera any more (lost in the divorce) so I can't post pictures of mine.  Cutting a new notch for the front tapper pin is very easy.  If you decide to do it and have any questions IM me.

Link Posted: 9/13/2003 2:21:25 PM EDT
That does look nice.  Did you cut down the gas block so there is only one pin holding it to the barrel?  Or, did you cut down a FIRSH?  I can't tell which way you went from the pictures.  

Whatever you did, it looks good and I'm jealous.
Link Posted: 9/13/2003 8:43:28 PM EDT
Thanks for the complements.  It's no FF RAS, but it does what I need it to do.

Kris, thanks for the offer.  I'll keep that in mind if anything unexpected comes up.

Scott, actually this rifle isn't complete yet.  You can't tell from the pic, but there's no gas tube or gas block under the FIRSH.  And the rear taper pin on the front sight base isn't driven all the way in.  The FIRSH is an unmodified midlength model.

Hopefully I'll remember to post another pic when the Leupy is mounted and I decide what to do with the front sight.
Link Posted: 12/29/2003 9:26:04 AM EDT
I finally got the rest of the parts together and zeroed this rifle over the weekend.
I decided to keep the front sight to make the rifle a bit more versatile.
I also added:
KAC 300m flip up rear sight
RRA 2-stage trigger
SPR grip



I only had cheap target ammo with me, all 55gr FMJ (American Eagle and Black Hills).  After sighting in, groups hovered around 1.75", but as I got used to the rifle/scope, they came down to less than 1.25" at 100 yds.

This was really my first time bench shooting with a scope, so I was more than satisfied with the results.  I'm confident that with a lot more practice and better ammo, I can shoot 1 MOA or less with this rifle.

In case anyone is wondering, the front sight is visible in the scope at anything less than 4x or 5x magnification.  I may add a flip up front sight in the future, but right now I'd rather spend my free time shooting it.
Link Posted: 12/29/2003 8:31:36 PM EDT
Good looking rifle; I'm glad it performs for you.

You should also post the pic of it against the wall; it's a surprisingly well-balanced looking package.. I think I'll go for something like it on my next build.
Link Posted: 12/30/2003 3:00:50 PM EDT
Thanks.  Not bad for a $65 used barrel from the EE.  Actually, most of the rifle came from the EE.  One of my goals was low cost without sacrificing too much quality.

I apologize for the lousy pics.  I'll get better ones up soon.
Link Posted: 12/30/2003 5:03:13 PM EDT
$65 barrel? I hate you..

I wish only someone made fluted midlength barrels..
Link Posted: 12/30/2003 6:21:45 PM EDT
[Last Edit: 12/30/2003 6:30:57 PM EDT by Onslaught]
I wish only someone made fluted midlength barrels..
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I bought a chrome lined mid-length RRA bbl from Pete in NH and sent it immediately to KKF to have it turned and fluted.  All told, it'll be $285 not including shipping.  If you just had it fluted, and not turned, it would be $255 which is about what a fluted Bushy would cost.  

I don't think Pete has any more chrome lined middies, but ADCO might.

Very nice rig BTW.  I see that you've settled on a decision, but I was going to suggest the DPMS low profile front gas block.  I think it finishes off the look very nicely because of it's tapered profile even though it does show a bit.

Link Posted: 12/31/2003 3:01:46 AM EDT
write or call the folks at
and ask them about their new specter kit. It looks like what your attempting to do. they do not have it on their page yet but can link you to a pic and pricing

Good luck
Link Posted: 12/31/2003 1:07:36 PM EDT
[Last Edit: 12/31/2003 1:09:35 PM EDT by M4-guy]
More pics.

Chopped gas block and front sight base:

Here you can see the barrel uses the regular carbine gas system, with the FSB in the midlength location.  It's basically a tweak of the Dissipator concept.  Note that the FSB was put on just for this pic.


The finished project, a bit different that what was originally planned:
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