Shortening gas tube & Tapering barrel to fit gas block: SBS conver

[Hudd 0]

Im about to do a 12" then 8" SBS saiga 12. I know the sizes i need to shorten/ move back my gas tube. My qustion is, how do you recontour/ taper the barrel so the gas block fits. If anyone has a few pics it would be greatfully appreciated.

[jdtravers 637]

You need to machine the barrel, outside diameter (OD) to match the Gas Block Inner Dimension (ID) on a lathe, and then machine in font of the new gas block location for the proper barrel OD. After, you TIG weld up the old gas ports.

 

If you do not have access to a lathe or the knowledge about this, then you are definitely in for a learning experience, maybe not all good!

 

It is NOT a taper cut. Look at your barrel now at the OD of the barrel where the gas block goes on in relation to the barrel and imagine moving the gas ports back 2-4 inches. That is what it should look like. Not rocket science. Exactly the same as it looks/measures now, but just move those dimensions back to where you want your gas block to be.

 

In other words, the only pic you need is the one of YOUR gun, after you remove the gas block!

 

Jack

[Cobra 76 two 2,677]

And you don't need to shorten the gas system on a 12"er. Just needs more and larger ports.

[Hudd 0]

Affirmative. Would machining the new locations OD to fit the ID of the gas block make it a lil loose, cause it requires a pounding to get off (like my gf, jk). Should i match the OD of the barrels new location to that of the old location were gas block used to be. In other words, matching the barrels OD from old to new, rather than the barrels OD to the ID of the block?

Also, when your weldn up them ports, do you get any drip down in the inside of the barrel, is the inside surface of those welds smooth, or does it not matter much?

[jdtravers 637]

I match the ID of the gas block to the finished OD of the barrel plus .0005 just tight enough that I can drill the new pin locations and the gas block will not move. Almost, but not quite tight enough that I can take it off by hand. Still needs a light press fit for seal.

 

Whenever you weld up a barrel or receivers you need to use a backer or a plug. I have machined my own rods/plugs to go inside the barrel (slip fit) when I weld and plates that I vise grip onto the receivers when they are welded. I use bronze for my backers as it is a dissimilar materiel and has better longevity than other backers.

 

Jack

[Hudd 0]

Thanks man, il post some pics/ vids wen im dun. Sttill in the prelim research stage.

[Hudd 0]

I match the ID of the gas block to the finished OD of the barrel plus .0005  just tight enough that I can drill the new pin locations and the gas block will not move.  Almost, but not quite tight enough that I can take it off by hand.  Still needs a light press fit for seal.

 

Whenever you weld up a barrel or receivers you need to use a backer or a plug.  I have machined my own rods/plugs to go inside the barrel (slip fit) when I weld  and plates that I vise grip onto the receivers when they are welded.  I use bronze for my backers as it is a dissimilar materiel and has better longevity than other backers.

 

Jack

What amperage and type of wire would you use to do that (Carbon steel wire)?  

Also do you cut the plugs at an angle because the ports are drilled at an angle?

What type of metal is a typical barrel made of (Carbon steel?), is it lined?

 

Any other words of wisdom or pics of your setup?

[poolingmyignorance 2,191]

Your backing plugs for the barrel should be cylindrical and large enough cover the gas block area. Yes the barrel is chrome lined, you  just need to make sure your plug is about .001" smaller than your barrel ID so you can push it out after you weld it.  

The barrel IS carbon steel, but is prone to porocity when welded. You definitely need to clean the paint from area and I like to chamfer the holes before filling.  If your not familiar with performing full penetration welds I'd suggest you get somebody who is to do the work, or you could end up with your welds becoming projectiles, or hot jets of gas venting through the top of your barrel.