The Space Cannon 308 pistol

11 1/8 inch gas tube from White Oak Armament.
Took the muzzle break w/flash can off and just going to try a plain flashcan.


Thank you very much! One more question. What is the gas port barrel diameter on the sig barrel?

“What diameter of gas block works with this barrel”


Drilled out to 5/64. 3/4" gas block
The 5/64 bit didn’t open it up much. I don’t have a numbered bit set. 1/8 " bit was smaller than factory gas port.


Thank you for the info! @shooterrex
I wonder if the original gas port size in the 716 barrel size would/ can work?

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I think you meant 1/16" was smaller than the factory gas port.

5/64" is 0.078125". My drill index is missing most of the bits smaller than #49 (those little ones are easy to break), but closest measurement I can get with the calipers, is the gas port is about 0.073" (give or take a couple thousandths).


Think jtallen over on is using the factory gas port. And yes the 1/8" drill bit was smaller than the factory port.


Ok!!! Thank you @shooterrex for planting the seed!

Here is my “ Little thumper” your guys at are a bad influence! Lol

The barrel is all that you would expect from Sig. chrome lined, extractor support in the extension of the barrel, recessed crown. Etc,etc

The gas port on this measured out at .068”

Note that a cheap drill bit set can double as a cheap pin gauge set.

In all honesty I felt a little weird about the lack of a proper “backstop” for the gas block to shoulder against.

So I machined a spacer out of 303 stainless that was .001 less in diameter than the outter diameter of the barrel.

After pressing it on the spacer onto the barrel I got the feeling I was working on an AK… yeah weird.

I had to shorten up a mid-length gas tube up a bit. This saved me time instead of ordering a custom length gas tube.

Ok, now it’s time for some insurance on this gas block staying put.

And then blue the barrel to protect it.

Upper and rail 89.99
Complete pistol lower with NiB trigger 249.99
BCG toolcraft 169.99
Gas block 19.99
Gas tube 7.99
Muzzle brake and washer 40.00
Nikon M-Tactical 1-4 scope 139.99
Rings 20.00
Charge handle 39.99
All in all not to bad in my opinion.

I do however wonder if I should get a heavier buffer weight in this. The current one seems just a little anemic.

With the stock fully extended this is at 33”
Not to bad for this little rig!

The balance is just a tad front heavy, but I don’t see it being a issue personally.

Now if I could only find time to hit the range!!! :joy:


Damn cool!!!


Thank you Brother! The real nice part is it didn’t break the bank!


Looks good. I just dimpled the barrel for the gas block and left it at that. The spacer was a good idea. Think I need to polish the chamber a bit. Start having exteaction problems after 25-30 rnds. Clean the gun and its good for another 25 or so. Havent checked the extractor springs yet. Need to do that too.


Interesting @shooterrex. Please keep us in the loop on your concerns with the extraction.


Don’t think I would do that… Could cause excessive bolt thrust! Lines in the chamber are actually helping with lockup, brass expands and locks case in chamber. I would think that maybe your over gassed…
Also when I machine dimples for the gas block I use a 3/16 end mill and cut so major diameter is just below diameter of barrel, not a center drill, helps with indexing/alignment.
Have you cronagraphed any shots, wondering how that shorty does on velocity…


Might be over gassed. Port drilled out to 5/64. I can try an adjustable gas block. I have a dimpling jig and it came with a bit to use. Just went in barrel enough for the set screw to have somewhere to go. I was going to use JB’S bore paste or toothpaste to use to pollish the chamber. Wasnt going with anything really abrasive.


Built one of these pistols almost two years ago now, hitting about 300 rounds and never had an issue. Never had to drill the gas port.


I did, used an H3 buffer in a Vltor A5 tube, the Vltor RE-10/A5SR


Yeah… I know they are the best for the AR10 action. I’m trying to stay budget minded with this one. Total is well under $850.00. I will most likely machine a heavy buffer for it.

I really appreciate the help @jtallen83
Do you have any pictures of the groupings I can expect from a build like this?

Note: I have no clue why it replies to @JPN ??? Not my fault :joy:


I like it!!


The Armalite AR-10 carbine buffer kit is $65, a bargain for what you get, call them if it is out of stock and they will fix you up;
I have been seeing 3/16 inch difference in the gas tube length with other peoples builds, my 11 inch has been the shortest I have heard of so far, so best to mock up first and get a good measurement before ordering the gas tube. Never took any pictures of the few groups I shot. Used Federal M80 ball and got 1 1/2 to 3 MOA groups, about the same as that ammo shoots in my 716 and other rifles. I have gotten 1 MOA with FGMM in my 716 so the barrel is pretty capable.


I can help, send it to me. I will permanently rent it from you for $1k, I’ll even give you a full review on its performance. Rental date to expire October 30, 2084. Then you can have it back.


Adjustable gas block is a very good idea for any AR platform! Provides a way to tune for different loads, makes the gun run smoothly and ruduces felt recoil…
Wouldn’t use any polishing paste either! Last thing you want to do is make a polished chamber, it decreases the friction coefficient! Bad idea, you want the case to lock in the chamber during firing.
Instead inspect your fired cases and look at the area around the extractor, if it’s pulled even slightly out your over gassed or timing is off, the gun is trying to pull the case out of the chamber before the pressure has dropped!
I see this problem often and people think they need to polish everything like that’s going to fix it, it’s not a 1911!