Adjustable gas block

[jameslovesjammie]

I am building a 6.8 SPC with the purpose of shooting jacketed for hunting and plinking with cast.

I am looking at a 18" barrel with a 11.25" twist and 5R rifling. The chamber is a 6.8 APR, which is an improved version of the SPC II.

I am looking to run in the 2000-2200 fps area (unless I get time to start paperpatching). The boolits I will be using will range from 110 grains and up.

I am thinking of running an adjustable gas block. This way I can up the gas a little for cast and still keep it from overgassing with jacketed. I am also looking to run an aftermarket piston system.

This will be my first AR build and any advise would be appreciated. I am just now buying parts for the build. I am buying parts a few at a time, and this build will likely take a few months before I am ready to assemble.

Any input would be appreciated! I have wanted to build a 6.8 since I first heard about the cartridge back in 2004!

[Idaho Sharpshooter]

I have a 300 BLK, and have the same plan you do. I went with the JPEnterprises adjustable block. I bought it because the top of the block has a picatinny rail, and the screw is accessible from the side. Others often have the adjustment screw inside a free floating forend and it can be difficult to access.

Rich

[jameslovesjammie]

Rich,

I will have to use one of those tiny gas blocks. I am wanting to "hide" it under my free float tube. The only part I have purchased so far is the new 1.5" Midwest Industries free float tube. I wanted a thinner tube up front for weight and ergonomics. I purchased the 15" so it almost goes to the end of the 18" barrel, which has a mid length gas system.

This is the long, skinny tube I purchased.

http://www.midwestindustriesinc.com/index.cfm?fuseaction=category.display&category_id=450

[RU shooter]

You could also go with a adjustable gas tube, I saw them in the Midway catalog Then use whatever block you want ,You would only need to drill a small access hole in the top of your tube. http://www.midwayusa.com/product/2979396319/mgi-adjustable-gas-tube-ar-15

[jameslovesjammie]

You could also go with a adjustable gas tube, I saw them in the Midway catalog Then use whatever block you want ,You would only need to drill a small access hole in the top of your tube. http://www.midwayusa.com/product/2979396319/mgi-adjustable-gas-tube-ar-15

THAT is interesting!

[Moonie]

In my Spec II 6.8 SPC I run from 134gr Cast with 18gr H4895 all the way up to full power 110gr SPH's, all with standard gas block, carbine buffer and spring. I'm not over gassed on the full power loads. The cast plinkers are probably a little under gassed but they cycle the action and lock back the bolt just fine. I have a 18" Bison Recon barrel.

[jameslovesjammie]

That's good to know, Moonie! Do you know, by chance, what velocity you are getting out of your light cast load? I have all the .277 moulds except for the newest Miha one. I can fit a low profile gas block under my free float tube, but am considering going with a micro to try and sneak in a Osprey piston kit.

I bet that Bison barrel is a shooter! From what I understand, Bison, Wilson, and ARP are the way to go in 6.8. I am going with a 18" ARP with the mid length gas system.

[Moonie]

I have not shot it over my new chrony yet but I will soon.