Noveske Switchblock Clamp-On Adjustable Gas Block Comparison

[DustEm]

Does anyone have more than one ar-15 barrel length equipped with a Noveske Swithchblock Clamp on adjustable gas block? I'm trying to possibly adapt a 20" model to a pinned 14.5" barrel, and am curious if the porting is different between the different model lengths, or if I can get away with just cutting back the gas tube. I'm early into my build and only have a stripped upper and lower at this time.

​

Edit: It appears from other forums I've read that the port sizes very, and tend to be on the larger size. I may be fine, worst case I have to bore the adjuster knob a bit.

 

[Kpquinn9100]

I’m trying to figure out what exactly it is you’re trying to do. If you don’t have the barrel yet why are you cutting a 20” barrel? Just start with a 14.5. Furthermore most 20” barrels are going to have a rifle length gas system so are you trying to keep rifle length gas system? Not even sure that’s possible with a 14.5” as the 16” dissipator style uppers put the fsb pretty close to the end of the barrel so you’ll have minimum room to put a gas block on and still have room for threads. 20” port size will be smaller than 14.5”. Which is fine if you’re running dedicated suppressed. But by the sound of it you’re not if you’re wanting to run a switch block.

 

[DustEm]

Sorry if it wasn't clear, I picked up this guy https://www.midwayusa.com/product/1023443340?pid=786610 last night highly discounted, but I wanted to use it on a shorter barrel.

From what I've gathered the gas tube & porting is kind of custom so you cant just swap it out on different length barrels willy nilly. You order the block & tube for the length of barrel you want to attach it to.

I'm considering cutting the tube down and upping the porting for the shorter barrel TBD.

Looking back I wonder if i should of gone with a piston system as I plan on running suppressed. They were NOT on sale haha.

 

[Kpquinn9100]

Ah ok. Yeah that particular one says 20” barrel. So I’d guess the port size on the block is a set size. Since this isn’t adjustable in theory if you have a 14.5” with the gas port size of .062 it doesn’t matter how large the size of the port is in the block because it’s only regulating .062 worth of gas. (As long as the port in the switch block is at least .062. Which it may not be being as it’s for a 20” barrel. That will lead into issues right away. ) Much like how an adjustable gas block works. But in doing this, I don’t think you’ll be able to switch it like it’s designed to do. Which essentially makes that feature useless. I don’t know how much of the pressure is diverted when the block is on and off. .062 is relatively “standard mil spec” sizing for 14.5 carbine length gas system. I’m just using that number for reference. May be a bit smaller or larger depending on barrel. (Assuming you stay carbine. If you go mid all that changes/dwell time etc is affected) It will shoot suppressed and non suppressed reliably so with block open it should cycle fine. However with block closed idk what it limits it to. A smaller port will run suppressed more “pleasantly” but you’d need to get the specs from noveske on before and after with 20” then make calculations with the port size you’re working with. In a nutshell there’s a possibility it can work, but at what cost? You might get lucky and it’ll run as it should suppressed and non but once you cut that tube you’re stuck with it. Gonna need a lot of trial and error for something an adjustable gas block can do with minimal effort.

 

[DustEm]

Ya I agree I may be putting way more work into it that I should. I personally just like the idea of a switch block more than an adjustable. Ease of operation and familiarity I suppose. I found this post last night. He says his 14.5/16" model on the S setting for 0.063" Which he thinks is large. I cant say I'm familiar with proper porting in that regard.

Preliminarily I found this last night. https://www.m4carbine.net/showthread.php?199715-Noveske-Switchblock-Info-Sharing-and-Modification



I also found this document. Kind of gives you an idea of different porting sizes. Tho most of them are just standard barrels, They do have a measurement of the Noveske 10.5" barrel switchblock S setting as 0.063 as well. I'll have to measure mine when it comes in. I'm guessing it will be smaller due to the barrel length.

 

[Kpquinn9100]

.063 for 14.5 seems average as I mentioned. Maybe large in regard for suppressed setting but in any case a 14.5 will cycle suppressed and non with a .063 port. That’s with a standard gas block. Of course it will cycle suppressed with a smaller port but as soon as you take the can off it’s gonna choke it. Which is where your idea with the switchblock would be ideal instead of using an Allen key or the like to count clicks on an adjustable block. (Which sucks btw. I have a temperamental 10” .308 sbr that I have to do this on with an slr block but it’s entirely necessary to even get the gun cycling with a can or not.) Guess you need to start with finding out port size in the block then move from there. In some cases rifle length gas ports will be larger but it’s all brand dependent as well as .223/5.56 etc so hopefully the port in the block follows this theory. In this case as long as the port in the block is larger than the port in the barrel it can be tuned. Reliably? Guess you’ll find out. Interesting concept here and I’d like to know the outcome when you find it. One benefit of an adjustable block is you can fit it under a rail though.

Interesting find on that chart! I mainly deal with 14.5 and under as I have multiple registered lowers but I do also own a few muskets haha. I also tend to make custom barrel lengths to fit rail/suppressor gap etc so I’m mainly measuring very similar gas port sizes along with knowledge of brands I know offhand. Good chart for reference though!

 

[DustEm]

Ya the way things are looking at the moment I'll need to buy a FSB rail, or mill my own. I have access to a mill, it will just be a bummer that I'll kill the finish on the rail by cutting it. I might hold off on purchasing a rail until I'm happy with the performance of the switchblock that way I don't go throwing money away if it doesn't work as expected. Worst case scenario I just save it for a 18" barrel build (which its designed for) and put a short rail on. I'll update this thread as I build my rifle, Which may span a while.