Relocating Gas Block Rearward

[lsxevo 9]

Hey guys, I have searched all over this forum and cannot seem to find a detailed thread discussing moving the gas block rearward on the S12. I know that several companies out there move the gas block back 2-4 inches to help cycling ammo on shorter guns, but can't find a DIY thread. I have acces to a metal lathe for turning down the barrel so the gas block can slide farther to the rear, but have multiple other questions reguarding this mod.

 

Do I have to replace gas tube or can I shorten the stock one?

How do I address the bolt carrier being too long?

How do I successfully weld old gas ports without penetrating into the bore? Drilling new gas ports?

Are there set increments(inches) in which the gas block can me moved to keep everything else functional?

[pedal2alloy 206]

It's not really a DIY project per se, but you could still do it.

 

The stock tube can be shortened and reused.

 

The bolt carrier has to be cut down & welded

 

To fill in old gas ports, you have to cover ("back up") the holes inside the barrel with something that won't stick to the weld, then TIG them up. If you have a little bit of weld protruding into the barrel, you can file it down with a make-shift extended file, or better yet it will get shaved off by "fire-lapping" ha.

 

Regarding the question of dimensions such as barrel length, gas block location and gas port size, and how they all relate to each other, guys like Tromix have figured that out by trial and error (expensive). So your best bet is to just pay him to do it for you. Or you can copy one of his guns, but don't tell him I said that.

[ramlake 98]

1. What length barrel?
   

[evlblkwpnz 3,418]

There is a lot going on there and I do not recommend doing it unless you are really good with your hands and very meticulous.

[jamen 8]

The best thread I found for this was here http://forum.saiga-12.com/index.php?/topic/38318-sbs-technical-info-thread/

 

To answer your questions: you can shorten the stock tube the bolt carrier piston runs in, but you'll run into trouble with the bolt carrier hitting the ribs. You can try to open it up, but it's easier to get a new piece of tubing.

 

Typically you remove the piston end of the bolt carrier. Tromix makes, and CSS sells, a shorter piston to replace it. I think that gets you about 2". If you want to move the gas block even further back than that allows, you have to make up your own solution; a shorter piston still, or have the puck impinge directly on a pistonless bolt carrier.

 

Welding the old ports pretty much requires a TIG or careful MIG, backing the area with a copper or aluminum rod that fits real well in the bore. You have to carefully clean the holes of any residual lead/fouling to get the weld to stick. Alternatively you could cover the holes with some sort of collar, might not look as slick, but could work. Pressures are not real high on a shotgun barrel. On mine the holes are covered by the muzzle brake device. It works fine. Tromix has made some guns with barrels short enough that the section with the old gas holes gets cut off and discarded. That's a nice solution.

 

Drilling new holes is pretty straight forward. I would use a small endmill to get angled pilot holes going, then open them up with a drill bit, but you can probably do it with a center punch and a drill, carefully. If you don't see yourself being able to come up with ways to do that step this might be a hard project to take on. Because as this project goes, making the new gas holes is one of the easier steps.

[TonyRumore 1,332]

You need to get these parts from CSS or MS Auto if you plan to move the gas block back 2.25".

 

[lsxevo 9]

1. What length barrel?
   

 

I cut the barrel to approx. 15.5" and permenantly attached a muzzle brake which makes it a little over 18".

 

There is a lot going on there and I do not recommend doing it unless you are really good with your hands and very meticulous.

 

I am VERY meticulous! It's almost scary......... Lol.

 

You need to get these parts from CSS or MS Auto if you plan to move the gas block back 2.25".

 

 

I guess those parts consist of a shorter piston and gas tube?

Edited July 27, 2012 by lsxevo

[lsxevo 9]

Tony, my plan was to find a piece of snug fitting copper tubing to go inside the barrel to weld against for the old gas ports. Is this similar to how you do them or do you recommend another technique?

[TonyRumore 1,332]

There is no need for any insert in the barrel if you're good with the Tig. A good Tig man can control the depth of penetration (especially if you have done several thousand) without the need for a backup. If you suck....well, maybe you should stick something in there.

[billyjoebob 10]

Do you really have to go through the effort of shortening the gas block for a 2.5" reduction in barrel length?

 

I thought the existing gas block could be tuned to compensate for much shorter barrels while leaving its length intact.

[romad7 75]

I went 3.75" shorter but you don't need that unless you are making an SBS. here is my thread http://forum.saiga-12.com/index.php?/topic/76696-my-first-gun-project/.

 

There was a comment about securing the spinning end of the gun in the lathe, if you don't remove the barrel I highly recommend this fix. Removing the barrel would be best if you can do it right. My mistake was in not securing it properly and that made it more difficult to do a good job.

 

If you go 2.25" definitely get the shorter piston rod, the gas tube looks easy to make but if the price is right might as well buy that too.

 

Most of what I learned to start is from the SBS Technical thread, lots of good info there.

[lsxevo 9]

Do you really have to go through the effort of shortening the gas block for a 2.5" reduction in barrel length?

 

I thought the existing gas block could be tuned to compensate for much shorter barrels while leaving its length intact.

 

In my case yes, shortening the gas block is required. This is only becuase I like to shoot low velocity(1100-1140 fps) ammo through my gun. I have already done all the mods a person could possibly do except for moving the gas block in reguards to cylcing issues. Drilled all 4 gas ports to .101, reduced recoil spring, polished all moving parts, etc. At this point, I cycle successfully 80%-90% of the time with low velocity ammo. Just trying to get that 100% cycle rate. Just remember, every Saiga is different!

 

I went 3.75" shorter but you don't need that unless you are making an SBS. here is my thread http://forum.saiga-1...gun-project/.

 

There was a comment about securing the spinning end of the gun in the lathe, if you don't remove the barrel I highly recommend this fix. Removing the barrel would be best if you can do it right. My mistake was in not securing it properly and that made it more difficult to do a good job.

 

If you go 2.25" definitely get the shorter piston rod, the gas tube looks easy to make but if the price is right might as well buy that too.

 

Most of what I learned to start is from the SBS Technical thread, lots of good info there.

 

I am glad you posted this info. I was wondering about turning down the barrel with the reciever attached. After reading, it appears it is better to take if off. Thanks!

[ramlake 98]

No need to remove barrel

 

Use an expandable collet or turn soft jaws, grab it by the I.D, and use a steady rest. Make a light qualifing pass end and then hold it on the O.D with 3 jaw. Turn the barrel back for the gas block then part off at the desired length. Setup on the I.D again and thread so the bore and threads will be concentric.

 

 

 

 

 

 

 

http://www.youtube.com/watch?v=FpHDwXN1hnk

 

Many of the forum business members can easily do this for you also.

Edited July 30, 2012 by RamLake

[lsxevo 9]

Alright guys, I finally got my barrel turned downed down in order to move the gas block 2.25" to the rear. I have developed a few more questions though....... How do I removed the factory gas tube from the sight block? Will the new Tromix shorter tube just press in? Another problem with my gun along with many others is the gas ports did not align with the block from the factory. You can see in my 2nd attachment that the ports are shifted a little to the left from the gas system placement. Having said this, what technique should i use to drill the new gas ports and ensure that they correctly align with the gas block. I just figured it made sense to correct the alignment problem since i am drilling new ports anyways.

[romad7 75]

One quick thing, when you drill for the gas block pins get it all straight, drill one and put the first pin in before drilling the second one. If you don't the drill bit might push the gas block a little and make the second pin more difficult to get in. I have this friend that did it wrong and it caused problems:-)

[robertparker999 3]

[Blue Flash 0]

I could use some help as well. What hand guard do you use when you move the gas block back 2.25 inches. Sorry for the newb question but I'd like to know and see pics if anybody can help.