AR 15 20 inch barrels?

[jmdavis]

No idea, it's the one that came with the CTR package when I bought it.

[Lonestar6]

That pretty well answers the question. The buffer is likely in the 2.9 oz range. I was wondering how, with the longer barrel, the gas pressure was impacted; but apparently it is not impacted enough to need a different weight buffer in your set up. That to me is a useful bit of information, thanks!

[henschman]

I have heard the H2 is the equivalent of the rifle buffer system in a carbine receiver extension.  however, I ran a plain old carbine buffer in my 20" AR for many hundreds of rounds and several Run 'n Guns.  It always worked great, so I never bothered trying anything else. 

I have since changed that rifle over to a Mapul fixed stock setup with A2 buffe.  That was done mostly for improved cheek weld for scope use.

[Lonestar6]

I have read about H2 and H3 buffers, but don't want to buy extra buffers than are necessary to switch between a 16 and 20 inch barreled upper. I prefer an adjustable carbine stock as my best LOP is a little shy of what the A2 stock accommodates. It is good to know I can start with the standard carbine buffer with some confidence.

[Bluesteel]

I just built a National match AR-15 with a Shilen 4-ratchet 20" service rifle barrel (came with hand lapped matching bolt), a Giessele NM trigger, Ares NiB BCG, Armalite FF tube (with standard A2 handguards) and clamp-on front sight.  For the buttstock, I  bought a UTG A2 kit (comes with buffer, tube and spring) from Dvor.com for $50 (they're on sale there right now for $47) and then bought an A1 buttstock shell and top screw from Fulton Armory for around $25 and replaced the A2 with the A1.  So now it's A1 LOP but with the A2 buttplate which has the checkered finish and sharper edges than the A1 so it won't slip when in the shoulder pocket.  Been busy so haven't had the chance to shoot it yet but Shilen AR barrels are supposed to be sub MOA with match ammo.

[Lonestar6]

That sounds like a sweet build. Thanks for the stock information.
LS6

[henschman]

The Magpul MOE fixed rifle stock is actually a little shorter than an A2 stock as well.  I had to add an extra-thick PRS butt pad to bring mine to ideal length.  It is a very nice stock -- I consider it a significant upgrade from the GI piece.  It is better for storage, since the entire butt hinges open, instead of just a little trap door.  Also it is set up to accept side mount QD swivels, which is how I like to mount my slings. 

[Lonestar6]

I have recently been drooling over the PRS stock for its adjustability for length and rise, but cannot justify the dollars.

[henschman]

I think that most average-sized folks would find the adjustable cheek piece on the PRS to be useless for Rifleman-style shooting, as it is well to the rear of where your cheek should be resting if you are turkey necked out.  If it were in the right place, it would interfere with the operation of the charging handle.  It is also inordinately heavy. 

[Lonestar6]

I had some of the same thoughts. With its charging handle, the m16/m4/ar15 platform was not meant to have a cheek riser.

[Bluesteel]

I find that almost all AR offset optics mounts are too high to obtain a good cheekweld but I like the height of the standard iron sights.  Armalite makes the only offset scope mount for an AR that is at the same height as the irons of an A2, and it's only $89 on their website.  Probably will interfere with BUIS though, so likely a good option only if you remove the rear BUIS or don't run irons.

[Lonestar6]

Thanks, I will check that out.

[509gman]

I find that almost all AR offset optics mounts are too high to obtain a good cheekweld but I like the height of the standard iron sights.  Armalite makes the only offset scope mount for an AR that is at the same height as the irons of an A2, and it's only $89 on their website.  Probably will interfere with BUIS though, so likely a good option only if you remove the rear BUIS or don't run irons.

Pm Itsansks. He's got a mount that gets you a perfect cheek weld and nose-to-charging-handle index.

[spitfire51]

I just built a National match AR-15 with a Shilen 4-ratchet 20" service rifle barrel (came with hand lapped matching bolt), a Giessele NM trigger, Ares NiB BCG, Armalite FF tube (with standard A2 handguards) and clamp-on front sight.  For the buttstock, I  bought a UTG A2 kit (comes with buffer, tube and spring) from Dvor.com for $50 (they're on sale there right now for $47) and then bought an A1 buttstock shell and top screw from Fulton Armory for around $25 and replaced the A2 with the A1.  So now it's A1 LOP but with the A2 buttplate which has the checkered finish and sharper edges than the A1 so it won't slip when in the shoulder pocket.  Been busy so haven't had the chance to shoot it yet but Shilen AR barrels are supposed to be sub MOA with match ammo.

Where did you find the clamp-on front sight?  I've been looking for one for a while but can't find them anywhere.

[Bluesteel]

Clamp-on is available from Armalite but you have to call them to get on a list as it's a special order now and not regularly stocked.  It took about 3-4 weeks to get mine.  The sales guys said that they probably weren't going to get stock in until spring, when folks are building up NM rifles.  Their's is the best, as it doesn't use set screws that gouge into the barrel.  They make 2 kinds, one with the sling mount and one without.  You do have to be aware of the spacing from the rearward face of the sight to the gas port though, as this is made specifically for NM builds and would require a spacer for most barrels (to make up for the missing handguard endplate thickness)

http://www.armalite.com/Catitem2.aspx?Category=07033031-2a2e-439c-a701-edf0d7327c93

In my searches for a clamp-on, this appeared to be the 2nd best option for the $$:

http://www.shop.dezarms.com/product.sc;jsessionid=C805801312359885F8CB50FE8639EE3C.qscstrfrnt01?productId=27&categoryId=8

[henschman]

I found a way of mounting a scope on an AR that gives good cheek weld and eye relief.  The 6" version of this YHM riser:  http://www.midwayusa.com/product/2696314296/yankee-hill-machine-extended-picatinny-style-riser-mount-ar-15-flat-top-matte?cm_vc=ProductFinding

Plus Vortex Tactcal Low 30mm rings are perfect for me.  It basically puts the sights at the same height as an A1/A2 rifle.  No, none of the folding rear sights I've had will fit under the scope.  That's OK -- I can zero a rear sight, remove it, and keep it in that Magpul buttstock (along with a full cleaning kit). The nice thing about the riser setup is that if your head size requires a different height, just use different rings.  Here is what it looks like on one of mine: