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Thread: 12.5" barrel build
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11 March 2018, 10:42 #1Senior Member
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12.5" barrel build
For whatever reason ever since I built my 10.3" SBR I have wanted t 12.5" carbine. I am starting with a pistol and plan on doing another form 1 for this lower. I finally committed to the build but need a bit of input in a few areas.
First thing I am looking for is my hand guard choice. There are very few choices out there when it comes to maximizing rail space for a 12.5" build. I am leaning in 1 of 2 directions at the moment. First is to run an SLR 11.5" Solo rail leaving minimal barrel space between my rail and SiCo Saker. The other choice I was debating was running a MI 12" suppressor compatible rail (which measures 12.65") which would leave my can slightly recessed under the hand guard. I am kind of leaning in this direction, however, I have concerns about being able to actually fire the rifle without the suppressor attached. I plan on using a Saker mount which looks to have a bit over an inch of area before the prongs open up. With the device mounted it seems like it should work, but I don't know for sure. If anybody has a 12.5" setup with pics, with either type of these options, that would be helpful.
Second thing. Gas block. My other SBR has a pinned gas block that is not adjustable. It is overgassed, but I have been able to tame it with a heavier spring and H buffer. I don't have any problems with gas in my face. I am thinking of doing an SLR adjustable block on this build with a clamp on style block. What is the consensus on this type of clamp on block? Good to go for hard use? Or, should I just get a set screw type and have it pinned?
Thanks guys!
Edit...barrel came today. Coming along nicely.
Last edited by rxer311; 14 March 2018 at 16:17.
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11 March 2018, 10:53 #2
SLR makes great blocks but on a 12.5 I would think it's easier to tame gas wise than a 10.5.
If you really want to adjust it you can fine tune it of course. I set my SLR adjustable blocks to run suppressed and non suppressed and haven't touched em since. You still might have to tune it with buffers and springs but I would think you could tune a 12.5 upper a lot easier on the backend rather than a gas block.
Personally I'm not a fan of clamp on blocks but that's just me.
As for barrels and hand guard choice someone here pointed out that one barrel manufacturer leaves their 12.5" barrels slightly longer so it will be easier to get a rail fit.
I forgot which company that is but it would open up more options for you.
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11 March 2018, 10:57 #3
Good timing.
I'm doing a 12.5" upper right now with a 11.5" Cross Machine Tool HDX Handguard.
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11 March 2018, 11:38 #4
12.5" barrel build
Rxer311, what barrel you going with? I hear VSeven will sell a reduced gas port 12.5 if you call in the order. That would come with pinned block.
I’d go with a dimple block if the barrel is dimpled. It indexes the block over the gas block without guess work.
I run a SMOS 12” with my 12.5 barrel.
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11 March 2018, 11:51 #5
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11 March 2018, 13:05 #6
I'm a huge fan of the 12.5" setup and thanks to fledge (I believe), one of my two uppers is a V-Seven barreled setup. Obviously your objectives may be different than mine, but here's what I came up with when I first built a carbine and then wanted a similar setup for a Mini-Recce.
For the carbine:
- I didn't want a "lightweight" build, but wanted to keep the weight down across the rifle
- It was planned to be a competition/class gun that would run a RDS and have a light for a night class/whatever work
- Was suppressor friendly
- I wanted a quad rail because I like quad rails, but there was some flexibility to that. More importantly, I wanted to maximize weak-hand position to get it as far forward as I could for comfort
At the time, a 10.75" rail was about all I could come up with. The finalist rails were a KAC URX 2, KAC URX 3.1, or a Centurion Arms 10". I went with the URX 3.1, but the CA rail is actually the same length as the bottom of the KAC rail. The top of the KAC rail extends out the .75". I know you want longer, but those were my options at the time. I also went with a CA 12.5" barrel. I was already a happy CA customer with my CA MK12 and the 12.5" has not disappointed with good ammo. Gas when suppressed isn't really an issue. Pic for attention...
Then came the Mini Recce...
- Wanted an accurized carbine
- Wanted minimal gas
- Wanted a quad rail for bipod mounting but still leaving room to "perch" the rail on a barricade (URX 3.1 fails at this, even on my SR-25)
- Wanted to keep the weight down otherwise
I ended up going with a URX 2 and a V7 barrel which has just been a lights out shooter (I have a thread here somewhere). As fledge mentioned, you can also get a reduced gas port for his 12.5" and 14.5" barrels, which I did. Unsuppressed, it's like shooting a loud .22. Suppressed, it feels like shooting a 14.5" carbine (a little bit of a push and recoil impulse). Again, sounds like you have more options to get a longer rail now, especially if you don't want a quad. Pic for attention...
I will add that this would all be solved if we had access to a GL/SSC rail...
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11 March 2018, 13:27 #7Senior Member
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I have a KAK industries 12.5" carbine barrel on order. It is not dimpled, however, I like how clamp on blocks will give even pressure around a barrel rather than being pushed from one side with set screws. I actually think it is the more foolproof way to secure a block.
Link to barrel...
https://www.kakindustry.com/ar-15-pa...elonite-barrel
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11 March 2018, 13:30 #8
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11 March 2018, 13:37 #9
gatordev, glad to inspire. Those rifles are hot.
The CA 12.5” barrel is now unobtanium. Wish I had grabbed one. I hear they are ported very well. Wish I had known VSeven could reduce the port back when I ordered mine.
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11 March 2018, 13:38 #10
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11 March 2018, 13:47 #11Senior Member
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I am not concerned about the accuracy potential, I just feel that a clamp on block is a more secure attachment method.
Probably just send it to Axlnut to pin a block for me though.
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11 March 2018, 14:45 #12
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11 March 2018, 16:21 #13Senior Member
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I think I am going to try the MI suppressor compatible rail and see how far recessed it goes.
I am thinking a 12.5" barrel with .6" for threading, so the muzzle device would start at 11.9". The rail is 12.65" so that is 0.75" of the muzzle device recessed. The mounting point for the suppressor is 0.25" from where the muzzle device meets the shoulder of the barrel and the tines of the FH start at 1.25". This means that the suppressor would be recessed .5" when mounted and the FH should clear the hand guard by 0.5" when the suppressor is not mounted.
Does 0.6" for threading sound right? If so, I think this setup will work well.
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11 March 2018, 17:37 #14
Beautiful gun gator. Dude you read my mind.
I'm planning a 12.5" Mini Recce. SBR'ed a Cross Machine Lower, going with SMOS 12.5" I had on a Shilen Blank. Will go with the 11.5" CMT Handguard and probably a Dead Air KeyMo mount for whenever my Sandman K gets approved.
Probably throw my EOtech VUDU 1-6 optic on it.
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11 March 2018, 22:09 #15