SBS Technical Info Thread

[BobAsh 582]

I apreciate all the valuble info on this thread and would like to give many thanks. I am in the beginning process of doing an SBS on my Saiga-12. The Form 1 with paid tax is on the way to the NFA branch of BATFE. I plan to have Tom at Cadiz Gun Works do the job for me and cut the barrel to the factory 16.5' to produce a factory correct Saiga-12 K. He did this gun under warrantee and did such a fine job that the gun runs on 1 oz. low brass Remington with the 19' barrel. The gun was a Vodka special and has three gas ports. I want to use this gun for our monthly subgun matches when we include the shotgun. We only allow the use of low brass bird shot and I would like this gun to continue running the 1 oz. low brass after the barrel is cut to 16.5'. Does two to three inches less barrel make that much difference in back pressure? Any reply would be appreciated.

 

 

Yes, a 16.5" barrel will produce less gas than a 19" barrel. There's no way for me to say whether or not it will run a specific ammo. I suggest you tell Tom your intentions when he does your work..

[macaholic 5]

I apreciate all the valuble info on this thread and would like to give many thanks. I am in the beginning process of doing an SBS on my Saiga-12. The Form 1 with paid tax is on the way to the NFA branch of BATFE. I plan to have Tom at Cadiz Gun Works do the job for me and cut the barrel to the factory 16.5' to produce a factory correct Saiga-12 K. He did this gun under warrantee and did such a fine job that the gun runs on 1 oz. low brass Remington with the 19' barrel. The gun was a Vodka special and has three gas ports. I want to use this gun for our monthly subgun matches when we include the shotgun. We only allow the use of low brass bird shot and I would like this gun to continue running the 1 oz. low brass after the barrel is cut to 16.5'. Does two to three inches less barrel make that much difference in back pressure? Any reply would be appreciated.

 

 

Yes, a 16.5" barrel will produce less gas than a 19" barrel. There's no way for me to say whether or not it will run a specific ammo. I suggest you tell Tom your intentions when he does your work..

 

Thanks for the reply Bob, I did talk to Tom but I didn't get into much detail and it was a while ago. He did tell me to send a box of the ammo I would like to run through the gun, so I guess we will just have to wait and see.

Thanks again!

[Shangrila 0]

A question for the gurus. I have read several modification tutorials that say to weld up the gas vent (the one normally covered by the handguards) when you SBS a Saiga 12. My question for the experts is, should that vent be welded closed to provide more gas flow or should it be left alone? I'm in the process of SBS my S12 and would like to hear what the known experts have to say, as it is much easier to leave it alone than to weld it up and have to reopen it. Thanks for your time and input, much appreciated.

[BobAsh 582]

On an 8" gun, the barrel is cut off before the gas holes so it's not an issue.

 

On the longer guns we weld them up, very carefully. It's up to you, but precious operating gas will escape from there and it's unsightly IMO.

[Shangrila 0]

Ok, that's what I needed to know. I appreciate it, just didn't want to weld it and then have to reopen it later.

[Shadoh 16]

Great thread with tons valuable information, THANK YOU!!

 

Now for my question that I hope is different enough to warrant some feedback ).

 

I want to SBS my S12 to 11.5 inches BUT I dont want to move the gas block. Its not because I dont think I can do it its because I want to keep my Chaos Tri Rail and not have to remove the top to get to the gas plug. I shoot the hell out of the Wallyworld cheap stuff including the Winchester value pack and I want to continue to do so as well as the occasional slugs and heavy shot when I can find it in stock for cheap. I know Tromix says to move the gas block but Cadiz and Lonestar both have 11 and 12 inch SBS's with the block in the stock location. I was told its a "Trade Secret" and to send the gun in if I want my gun that way but if I cant do it myself then I wont have it done, thats half the fun of this gun, at least for me anyway.

 

Is there anyone with an SBS that short with the stock gas block that is still able to shoot whatever loads he wants that could throw some info/advice my way? I don't want to steal anyone's business or give away any top secret technology but come on, this isnt rocket science ), I will figure it out eventually I would just rather take the shorter road to get there especially when it comes to modifying hard to replace parts.

 

Second question, when you SBS your gun and you add a brake or breacher do you have to permanently attach it? Its seems like every time I see a post with an SBS they have the brake permanently attached. As long as the actual barrel is the length I apply for cant I hand anything off the end of it I want to?

 

Thanks guys

[Shangrila 0]

Hey Shadoh, I'm in the same boat as you. I really like the lenght of the 11.5" and am in the process of tuning it now. I can answer the second question fairly confidently; with the SBS you can put whatever you want on the end. I think most permanently attach to prevent it from flying off during heavy firing. I have and use the Russian choke set along with a Paradox choke for slugs and haven't had any problems yet. Mine will cycle high brass all day long after I opened the 4 ports to I believe .093 each (I'd have to check). I'm going to follow Bob's and others advice and close the gas vent on the outside. I am using a TAC47 auto plug, so I'm not worried about over gassing. I had Cobra do the bolt/bolt carrier reprofile and polish and bolt hold open mod. I also polished the hammer face to try to make it cycle easier. I hope this helps, as I am learning as I go too. Good luck.

[Shadoh 16]

Thanks for the reply.

Why do they recommend closing off the outside vent? After gas gets to that side of the puck its already wasted. If you block it off it would only add back pressure on the wrong side of the puck. I figured it was there to bleed off any gas that slipped by and blow out any crud that managed to make it that side of the puck. Look at its location, all the way forward and angled down. If it wasnt there the only place for that gas to go would be down the gas tube and into the guns action.

[Shangrila 0]

Thanks for the reply.

Why do they recommend closing off the outside vent? After gas gets to that side of the puck its already wasted. If you block it off it would only add back pressure on the wrong side of the puck. I figured it was there to bleed off any gas that slipped by and blow out any crud that managed to make it that side of the puck. Look at its location, all the way forward and angled down. If it wasnt there the only place for that gas to go would be down the gas tube and into the guns action.

 

 

I'm definitely not an expert, but I would say it is there to allow excess gas to bleed off prior to entering the gas tube, as you've said. I imagine the location is so that it is concealed by the handguards to prevent things from getting in there as well as gas getting out. I'm using the TAC47 plug as a safety measure so that the excess gas has somewhere to go other than the action on rounds that would otherwise be "over gassed". If I read Bob right, by sealing it off, it allows greater pressure to be developed than if you opened the barrel gas ports up more. Also, be careful when opening the barrel ports because if you open too far, you will eat the web between the holes out. Anyway, like I said, I'm definitely not an expert, just feeling my way through this by the experience of others and some trial and error. Good luck.

Edited October 8, 2010 by Shangrila

[mgconnor13 206]

A 12" SBS is doable. I opened my 3 ports and added a forth. Also polished up the bolt and hammer. It's a little bit of trial and error till you get the results you want. I've found that the tighter the choke you have the better the cheap shells cycle, with a turkey choke my 12" cycles any shot I put through it.

[gremlinx 20]

Great thread, I feel like I could build one with the help of others.. I feel guilty, using this inside info!!!

[csmw 98]

 

I want to SBS my S12 to 11.5 inches BUT I dont want to move the gas block. Its not because I dont think ...I shoot the hell out of the Wallyworld cheap stuff including the Winchester value pack and I want to continue to do so

 

Is there anyone with an SBS that short with the stock gas block that is still able to shoot whatever loads he wants that could throw some info/advice my way?

 

I have done about 15 (give or take) 12"-12.5" SBS's for friends (at no charge) back in the day (2005?). I think I might have sold one gun....the rest were done for free.

 

I originally did 5-ports (enlarged) and then went to (smaller) 6-ports later on. I don't remember the port-diameters.

I made some adjustable regulators, but later on just started modifying the factor regulators by dremeling several rounded notches in them, around the diameter. I would run the regulator wide open on low brass. Never had any cycling issues.

 

With polishing internals, throating bbl, etc....they all ran 100% on Federal-bulk and close to 100% on Winchester-bulk.

 

 

Early 5-ports (went to 6 smaller ports later on...

[mike12345 18]

whoops, I already posted on page two.

Edited January 28, 2011 by mike123456

[macaholic 5]

Hello Tony, it's been a while sinse I've been on this thread, but I have two form 1's on two Saiga 12's that I'm going to SBS to 16'. One of them has four gas ports and the other has three. My question is how large should I go with the ports on the four port gun? Also, I want to add a fourth port to the three port gun, but I'm afraid I may not have enough room after reading one of your posts concering the location of the gas ports. If I cannot add a fourth port, how large can I go without causing excessive fouling in the three port gun? Any addvice would be appreciated

Edited September 26, 2011 by macaholic

[romad7 75]

"You need to weld an extension hood back out over the top cover or it will eventually pop out of its track in the front.

You can get away without it about 50% of the time, but the other 50% of the time the gun will be like a boomerang and come right back to you for rework. About 10% of the guns have bolt/carriers that will ride up so high when the carrier comes out of the gas tube that the bolt is pulled away from the ejector and misses it. So....on those guns, you need a shim under the front of the top cover to keep it down in the pathway of the ejector. There is no way to tell which guns will be affected until you shoot them. You can leave the shim out too....but you'll have about a 10% boomerang rate with that as well. Now you're at about a 60% return rate, calling me, and asking me what to do. Just print off this post and keep it handy.".

 

Does anyone have some good pictures of the extension hood and top cover shim? I am sure that I could make something work but I prefer to learn from the masters vs reinventing the wheel.

 

Thanks

[ARod206 0]

Okay so I've been reading around for a bit and no one seems to talk about gas issues with going 8" SBS. I just finished up an 8" and the thing runs like a rape ape! Its just a continuous fireball out the muzzle, so much so that the op rod broke! literally cracked! I also noticed that the carrier is hitting the rear of the receiver. I've read that people are using 1911 springs some say to try an adjustable gas port. others say hog out the gas ports... I cant seem to get this to slow down any ideas? here's some of the specs: 8" barrel gas block moved back 3.75" 4 gas ports opened .004 over factory spec. Wont cycle 00 buck Winchester super X will cycle Fiocchi 00 , running winchester and federal 1oz slug

[romad7 75]

 

 

Does anyone have some good pictures of the extension hood and top cover shim? I am sure that I could make something work but I prefer to learn from the masters vs reinventing the wheel.

 

Thanks

 

Disregard this question, I figured it out.

Edited May 12, 2012 by romad7

[romad7 75]

Okay so I've been reading around for a bit and no one seems to talk about gas issues with going 8" SBS. I just finished up an 8" and the thing runs like a rape ape! Its just a continuous fireball out the muzzle, so much so that the op rod broke! literally cracked! I also noticed that the carrier is hitting the rear of the receiver. I've read that people are using 1911 springs some say to try an adjustable gas port. others say hog out the gas ports... I cant seem to get this to slow down any ideas? here's some of the specs: 8" barrel gas block moved back 3.75" 4 gas ports opened .004 over factory spec. Wont cycle 00 buck Winchester super X will cycle Fiocchi 00 , running winchester and federal 1oz slug

 

 

Do Not install lighter springs, you will just get more damage. What setting/gas plug are you using?

 

Pics of the damage would be good. Do you mean that the end of the carrier is damaged? The op rod should have been cut off in that build.

 

Did you install a shim on the dust cover to keep the carrier from rising up?

Edited May 12, 2012 by romad7

[Hudd 0]

SPAS-15 is correct. Custom job done by Tone for JeauxE.

 

Here's some velocity stuff...interesting

 

 

OK so I finally took most of the shotguns out for a spin on the old Chronograph. What I found is that, basically, those of you chuckleheads with no empirical data who have been yapping your cockholsters about how short barrels on shotguns seriously affect ballistics are fucking wrong. Lots of wrong. Like I said long ago, shotgun powder IS pistol powder- it burns fast and quick, and barrel length doesn't fucking matter that much.

 

I can't .PDF a spreadsheet on this computer so I'll get really slow and dumb like those who talk out their ass about ballistics with no basis in reality and list the average FPS for the shot strings.

 

First, using shitass birdshot- 12 gauge, 2 3/4 inches, 1 oz shot

12" barrel average FPS- 1040

14" barrel average FPS- 1069

18" barrel average FPS- 1114

19.5" barrel average FPS- 1114

20" barrel average FPS- 1108

28" barrel average FPS- 1159

 

Then using Remington 00 Buck-

12" barrel average FPS- 1121

14" barrel average FPS- 1127

18" barrel average FPS- 1216

19.5" barrel average FPS- 1205

20" barrel average FPS- 1182

28" barrel average FPS- 1250

 

Wow- 119-129 FPS velocity loss in 16 inches of barrel. That's devastating. Oh wait- no, it's actually not, it's fucking nothing at all and is actually about the same velocity variation in factory loaded ammo. I will feel as comfortable fucking up a bear using a shotgun with a 12 inch barrel as I would using one with a 28 inch barrel. Those of you clammering over 20 gauge Serbu Super Shortys rather than the biting sting of a 12 gauge to dust up a gravel pit should stick with the shortest of shotshells. I wouldn't want you to drop your purse while shooting.

 

[Hudd 0]

 

I want to SBS my S12 to 11.5 inches BUT I dont want to move the gas block. Its not because I dont think ...I shoot the hell out of the Wallyworld cheap stuff including the Winchester value pack and I want to continue to do so

 

Is there anyone with an SBS that short with the stock gas block that is still able to shoot whatever loads he wants that could throw some info/advice my way?

I have done about 15 (give or take) 12"-12.5" SBS's for friends (at no charge) back in the day (2005?). I think I might have sold one gun....the rest were done for free.

 

I originally did 5-ports (enlarged) and then went to (smaller) 6-ports later on. I don't remember the port-diameters.

I made some adjustable regulators, but later on just started modifying the factor regulators by dremeling several rounded notches in them, around the diameter. I would run the regulator wide open on low brass. Never had any cycling issues.

 

With polishing internals, throating bbl, etc....they all ran 100% on Federal-bulk and close to 100% on Winchester-bulk.

 

 

Early 5-ports (went to 6 smaller ports later on...

[operationlattethunder 1]

Old thread, but the best spot for this question I think...

 

I've got the Tromix shortened op-rod and gas tube installed, and I'm measuring and marking the barrel before I chuck it in the lathe. As I'm test fitting parts, I notice that the op-rod is still too long. With the factory gas puck and factory 2-position regulator in place, the op-rod bottoms out on the puck before the gas tube fully seats onto the gas block. It comes up about 1/16" short.

 

Obviously something has to be shortened, either the regulator, the puck, the op-rod, or the BC where the shortened op-rod threads in. I'm leaning towards the latter, but wanted to see what the preferred method was.

 

Thanks,

-Aaron

[operationlattethunder 1]

A pic of the gap I'm speaking of:

[zaxon_182 44]

I had the same issue with my form 1 SBS. I put the puck on the lathe and cut both sides down until it fit because I had already installed and pinned the short op-rod. Hopefully you get a response from someone with more experience than I.

Edited February 22, 2014 by delNbones

[operationlattethunder 1]

The more I think about it, I'll probably take it off the op-rod and re-contour it. After all it's only a $25 part and it's easily accessible if I need to replace it. Also, that would let me run my CSS puck and my Auto Plug, both of which are longer than the factory bits. Like you said though, I'm hoping a few others chime in.

[romad7 75]

The more I think about it, I'll probably take it off the op-rod and re-contour it. After all it's only a $25 part and it's easily accessible if I need to replace it. Also, that would let me run my CSS puck and my Auto Plug, both of which are longer than the factory bits. Like you said though, I'm hoping a few others chime in.

Yes, if anything needs to be modified, mod the part that is easily replaced or fixed (not the carrier). I think you know this but just confirming.

 

I guess you could cut the puck down but it is that size for a reason so I would be slow to mess with that. The OP rod is the best part to adjust to get everything fitting properly.

 

Oh and if you haven't already drilled the 2 taper pin holes in the side of the gas block make sure you drill one and install the pin before doing the second one. I drilled both before installing a pin and the bit walked a little on the second one causing the spacing to be off.

[poser 0]

When shortening gas system 3.75", where do you cut the carrier?  when I measure 3.75 from the end of the piston, looks like I have to cut all of the piston off and the nose of the carrier.  Is that right?

[romad7 75]

That's what I ended up with, just make sure you pin or weld the leftover threaded portion before using it. I didn't and now have an empty cavity where the op rod used to be.

 

When you cut it, leave a little extra and grind a little at a time until everything locks up correctly.

 

Also, don't cut the carrier. You shouldn't need to and replacing it is expensive.

 

Here's my process. http://forum.saiga-12.com/index.php?/topic/76696-my-first-gun-project/

Edited March 14, 2014 by romad7

[operationlattethunder 1]

Finally got this thing done. Did pretty much all myself, except a bit of lathe work, where I "supervised". It cycles low brass on a test fire, and it's the first SBS I've seen with the Chaos quad rail. Originally went for 11", but cross threaded the muzzle and had to cut it off and re-thread, so 10" now. Gotta fire off the amendment to my length to the BATFE. Pretty happy. Just gotta bead blast and paint.

[url=http://smg.photobucket.com/user/OperationLatteThunder/media/Mobile%20Uploads/IMG_7435.jpg.html]

Bad link. Sorry.

 

[BobAsh 582]

Looks good.  Nice job.

[Hudd 0]

Good idea.

 

8" Standard Tromix.

 

8" W/ Long Tromix Handguard

 

8" W/ Tapco Galil Handguard

 

 

12" Halo Handguard

12inchloaded.jpg

 

12" Factory Handguard

Aw man, where did all the pics go?