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Saiga 12 Loose Piston vs. Tight Piston : More Likely to Break Carrier?


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I'm hoping this thread can serve as a continuation of the discussion started by forsaken352 after breaking his bolt carrier.

I figured this was a topic important enough to warrant it's own discussion.  My post from that thread is below to get things started.

 

 

Posted Today, 08:51 AM

Loose pistons are expected and even arguably preferable on an AKM.   Is this not the case with the S12?  Is a wobbly piston a liability on an shotgun?

Almost all of the S12 bolt carriers I've had a chance to handle have little to no wobble in the piston.   

On the AK, a little wobble is intentionally put in to allow it to function with a slightly canted GB/RSB.  If an S12 has a loose piston, does that mean they built it that way on purpose to accommodate a variance in the particular gun it's going into?  In other words, do the factory workers check to see if a piston is rubbing, and then loosen it if it is, or is the amount of slop determined more by how much Ivan happens to care that day.   I don't believe we have any former Izhmash Factory workers here on the forum, so obviously I'm just looking for opinions.

 

I can see how having play in a piston would make it more likely to crack the carrier, but the fact that this is standard on AKs made it something that never concerned me.   I'm hoping the experts here might chime in and give their experience regarding this.  Of the broken carriers you've seen, did they all start out with loose pistons?  Have you ever seen a broken carrier on a gun that came with a tight piston?   Have you ever seen a case where tightening it on a well running gun caused issues with cycling due to the piston binding?

 

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Excellent question. I will step up to the bat and take my swings. The rifle versions of the AK piston are usually pinned or "thru riv-ited" to the carrier as well as being screwed? The Saiga 12 piston is only apparently "divi-ted", (sp?) by squashing the carrier after the piston is screwed into the carrier body.

 

Method of attachment? What may cause S12 carrier failures is that the piston may not be fully torqued up against the carrier. The bottom of the piston shaft may not be fully contacting the carrier body on every shot. The div-it (shitty spell check today) is taking most of the stress ... or perhaps only the threads?

 

Thus a weakness with the eventual fracture of the end of the carrier body? A cure may, (may) be to somehow unscrew the piston from the carrier and re dress the threads, then re torque the piston all the way into the carrier body? Dunno. Then cross pin the threaded union so things will not work loose?

 

I am also not sure if any eventual looseness in the piston to carrier fit with AK rifles is intentional or not. Maybe, maybe not. But the rifles have a better way of locking the piston shaft to the carrier. The S12 does not. Intentional? Dunno. Stressing just the threads may or may not weaken things? Dunno.

 

Maybe it is just an individual manufactures way of doing things, like the many different ways WW2 .30 Caliber M1 Carbines were made. A good corrective action with the S12? Remove the piston, redress the carrier threads, reinstall fully and then install steel cross pins? You want the thing to disassemble.

 

Also would be a good time to install that USA made piston for 922® compliance.

 

HB of CJ (old coot)

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IMHO the reason we are seeing all these cracked bolt carriers, and even some with whole chunks being broken out in front of the dimples pressed in the sides, is because this method of securing the piston ( / op rod) from unscrewing is not a good idea in the shotguns. It may be fine for the rifles because they don't suffer the same kind of brutal blunt force impact placed on the S-12 and Vepr 12 pistons. IMO there are three big issues that are causing the S-12 carriers to crack & break.

 Just as our buddy old coot mentioned, the pistons are not threaded all the way into the base before the machine pressed dimples are put in the sides to keep them there (1). This means the pistons are not transferring the blunt force being applied to them by the puck (2), directly to the mass of the bolt carrier the way they should be. If they were through riveted or pinned in place like Kalashnikov originally designed the AK carriers / pistons, then that would definitely help transfer the shock put on the threads every time the puck smacks the end like a hammer. (unlike the rifles that don't experience that metal on metal impact every shot...) That isn't the case though. Instead all that force is placed on the threads themselves, and even more so on those two very small points where I feel the strength of the steel in the carrier has been compromised by all the pressure (& resulting heat??) from being pinched like it has (3).

 The wobble of the piston is up and down because it's pivoting on the dimpled points in the sides, the same way an AK rifle piston does on the through rivet. I believe they were designed (in the rifles) to be able to wobble up an down a little to aid them in staying fluid in the flex and movement inherent in the design of the AK's loose tolerances. It basically allows the inner surfaces of the gas tube to easily guide the piston into the sweet spot so it hit's the hole in the gas block without having too much drag (friction) put on it by a stiff piston having to rub harder on the gas tube as it rocks along it's path. (watch some slo-mo vids...). This vertical wobble undoubtedly places a lot of stress on the 6 and 12 o'clock positions of the threaded hole in the front of the carrier. BUT... that is not where we are seeing cracking problems. They are cracking at the 3 and 9 o'clock positions directly in front of and leading to the weakened dimpled spots.

 

My conclusion.... The pistons & carriers are far more likely to survive all that punishment if a correction is made in this bad design flaw, and a through rivet (steel pin installed through the center with both ends pressed into drilled and beveled holes then ground / sanded flush) installed. It is also useful IMO to go ahead and install a Tom Cole US made piston while you are at it. Not only are they much more stout than the factory pistons (which I have actually seen some bent / broken ones), they are made longer so if installed correctly like I do them, with a matching bevel on the end to the beveled edged base of the hole drilled in the carriers, they can be firmly seated solid steel to solid steel in the carrier. That way the threads are not taking any stress. Then to finish it out properly with the through rivet, what you end up with is something many times stronger. I ahve done a LOT of these for our customers over the years using the Tom Cole HD pistons and through riveting the factory ones. I have never once heard of the lessened wobble causing any problems afterward.

 It is my opinion that the way the puck puts more of a straight back direction of pressure / travel on the carrier than the rifles getting rocked upward by direct gas impact, it is more forgiving to a stiff carrier / piston when finding it's way back to the hole on the return stroke.

 

 As far as repairing carriers that have already cracked, and / or through riveting the ones which haven't cracked (yet?), I believe doing this through rivet vertically is the best method on carriers where the factory piston is retained (instead of swapping for a Cole HD...). Then on the cracked ones the threads will be re-tightened by the rivet before being welded and ground back flush.

 On carriers with the piston replaced so it is transferring the energy more efficiently, drilling out the pressed dimples and installing the rivet horizontally is acceptable. I believe without replacing the piston though you are better off with a vertical rivet and drilled slightly forward where it's still in the thick part of the carrier but is going through a more central part of the piston's threads. I have pulled a lot of them out and many have the dimples pressed very close to the end of the threads (like almost missing them off the end of the first threads). I think this is why some have much more play than others. On these carriers in particular, it makes much more sense to me to through rivet them vertically and farther forward.

 My own Vepr 12 piston for instance... it has about 1/4" of up and down play and is the worst I've ever seen. I'm planning to repair it to make it more solid but first want to see how long it will keep shooting this way. I shoot a good bit of magnums, mainly slugs through this shotgun so if it's gonna be a problem I will for sure find out eventually.

 

2c.gif

 

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Kind of sad reading this I had a loose piston on my lsa saiga and sure enough it cracked!! Kind of giving up on mag fed shotguns.....

 

It sounds like Cobra can fix this for you.   Don't give up on these Russian shotguns.  When you get them running right, there's nothing else like them.

Cobra is great guy and I'm sure he would be happy to help.  Click his link above to contact him.

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I'm really surprised that there aren't more posts on this topic.   How about if I put it another way.
How many of you have loose pistons and lots of rounds through the guns without any sign of bolt carrier cracking?

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I agree with Cobra on the sub-standard factory method of attaching the op rod to the carrier.

And even though not many op rod heads popped off, one is too many for me. It needs to be a stronger part (IMHO).

 

I have an '08 S-12 that had the typical small amount of movement on the op rod. I shipped the carrier off to Cobra with a HD op rod when Tom Cole had the first batch of them available. I think mine was the first or one of the first Cobra installed.

 

There were plenty of carriers and rods breaking back then and it was a relatively small cost for what I think is a big improvement in reliability.

 

If I found a mechanical link like that in some other machine, like maybe a tie rod on a car, it would be unacceptable there too (again IMHO).

Edited by Spartacus
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By the time it's threaded and pinned, it doesn't have a lot of meat at the critical points.  Now that there are aftermarket versions of carriers and op rods, a new method of joining them should be introduced.  I'm thinking something like a U-joint, or better yet a design like a wobble socket

 

post-1629-0-67630500-1416718334.jpg

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my carrier broke after about 5k rounds. the piston fight was rather tight, when compared to the other 5 or 6 Saigas I've had a look at - i.e. minimal wobble.
I had it welded together (no wobble now) and hoping for the best, but the Russian and Czech IPSC shooters told me that this will not last.

 

I've been looking to get my hands on a R&R carrier - maybe the Swedes can help me now.

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my carrier broke after about 5k rounds. the piston fight was rather tight, when compared to the other 5 or 6 Saigas I've had a look at - i.e. minimal wobble.

I had it welded together (no wobble now) and hoping for the best, but the Russian and Czech IPSC shooters told me that this will not last.

 

I've been looking to get my hands on a R&R carrier - maybe the Swedes can help me now.

 

You shoot a lot of rounds, let us know how that welded joint holds up.

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  • 2 weeks later...

I'm really surprised that there aren't more posts on this topic.   How about if I put it another way.

How many of you have loose pistons and lots of rounds through the guns without any sign of bolt carrier cracking?

I have an old, old saiga that has lots and lots of rounds thru it. My piston moves a hair if you attempt to snap it like a stick. It has always had this play in it. Never had a problem. Internals look perfect.

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thats strange,,my vepr12 has the same wobbly piston issue..so far no cracking or breaking..should i be concerned?

 

I would do something about it (and I did on my S-12).

I guess it depends on how you use the gun and what you expect out of it.

 

Anybody seen reports of the Vepr's having the same cracked carriers and broken op rods as the S-12's?

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what wou

 

 

thats strange,,my vepr12 has the same wobbly piston issue..so far no cracking or breaking..should i be concerned?

 

I would do something about it (and I did on my S-12).

I guess it depends on how you use the gun and what you expect out of it.

 

Anybody seen reports of the Vepr's having the same cracked carriers and broken op rods as the S-12's?

 

what should i do to fix it?is there a tutorial guide out there?

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what wou

 

 

thats strange,,my vepr12 has the same wobbly piston issue..so far no cracking or breaking..should i be concerned?

 

I would do something about it (and I did on my S-12).

I guess it depends on how you use the gun and what you expect out of it.

 

Anybody seen reports of the Vepr's having the same cracked carriers and broken op rods as the S-12's?

 

what should i do to fix it?is there a tutorial guide out there?

 

The consensus is to leave it, loose is better

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what wou

 

 

thats strange,,my vepr12 has the same wobbly piston issue..so far no cracking or breaking..should i be concerned?

 

I would do something about it (and I did on my S-12).

I guess it depends on how you use the gun and what you expect out of it.

 

Anybody seen reports of the Vepr's having the same cracked carriers and broken op rods as the S-12's?

 

what should i do to fix it?is there a tutorial guide out there?

 

It may run a long time like that voonman, but it does take a pounding and will fail eventually.

There's an old axiom in the computer biz..... "What percentage of hard drives fail?  All of them, it's just a matter of time."

 

I guess I hold the unpopular opinion that the loose movement and pounding on that loose threaded joint is a problem.

Read through the earlier posts in this thread from Cobra and myself.

 

I sent my carrier to Cobra to have him fix it. I converted my S-12 myself, but I wanted Cobra to fix the carrier. That particular

job is a bit beyond my skill set and my tool set.

 

I chose to spend the money on upgrading the reliability of my S-12, I felt it was important. Still do.

 

In spite of the differing opinions, there is a problem with the carrier/op rod joint on the S-12.

There are plenty of pictures of broken parts to prove it.

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  • 1 year later...

 

my carrier broke after about 5k rounds. the piston fight was rather tight, when compared to the other 5 or 6 Saigas I've had a look at - i.e. minimal wobble.

I had it welded together (no wobble now) and hoping for the best, but the Russian and Czech IPSC shooters told me that this will not last.

 

I've been looking to get my hands on a R&R carrier - maybe the Swedes can help me now.

 

You shoot a lot of rounds, let us know how that welded joint holds up.

 

 

Approximately 2k rounds later the carrier broke again. This time the carrier snapped into two pieces; a bit further back (at the recess for the cartridges, obviously there is quite a bit of notch effect going on). So right now I'm stuck with a broken gun, several choices (R&R carrier, new saiga, Utas XTR ...) and LOTS of frustration, since I was shooting fast and well and had good chances for the podium until the gun started acting up.

Anybody makes an Open shotgun which is not a piece of crap?

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Dunno about the S12 Open Gun.  R and R Targets does sell their own very high quality S12 carrier and S12 complete bolt?  I think their carriers can be mod-ed back to a right hand charging handle?  Dunno.  R and R Targets has a site here.  Good luck.  So far so good with "Betty Bucker", (our S12) but she has less than 500 rounds through her.  Barely broken in?  Dunno that either.  :)

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I've made quite a few 3 gun race guns and find that, if left unmodified,  eventually most of the bolt carriers crack on high round count guns -  especially if  the gun is tuned for birdshot, then used with 3" turkey loads, or buckshot for some match stages.  The solution that works 100% for my guns is to drill out the dimples right away before the carrier cracks.  Remove the original op rod.  I put in a brass insert, (shown in the picture) then TIG weld up the holes.  With the brass plug in place during welding,  the threads are pretty good after welding.  I clean up the threads with a tap.  I then make a titanium op rod with a stepped down end (i.e. the last few threads removed) so it seats firmly against the bottom of the threaded hole.  The load is no longer on the threads or the dimple, but directly on the carrier.   I've had no alignment issues with this technique. The Tom Cole op rods are great -  very heavy duty -  but also very heavy, hence why I prefer the titanium.  . FYI the threads are M12 x 1.25   This TIG welding technique can also be used to repair a cracked bolt carrier as well.   I've never had one I couldn't save.

post-31037-0-30149200-1472524822_thumb.jpg

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I posted about it last year, but when my original carrier cracked, I bought a couple of the take-off carriers that R&R had from new Saigas (don't want the relocated charging handle of their new carriers), and modified the one I used to remove all of the play from the joint.  I drilled out the dimples, removed the extension, and stacked washers under it inside the carrier to maintain the original length dimension while allowing it to be tightened down snugly.  Then I drilled through vertically (90 degrees off from the original dimples) for an AK gas piston rivet, and took it back apart.  I put Rocksett on the threads, and put it back together.  Tightened the extension until the hole aligned, and installed the rivet.  Resulting installation is tight with no movement whatsoever.  I had bought one of the heavy Tom Cole extensions, but I chose not to use it, because I think the additional weight just exacerbates the problem.

 

I haven't fired it as much as I would have liked since then, but it seems to work fine.  At some point I may look into sending my original carrier to Cobra for a weld repair, but for now at least I have a good carrier in my SBS plus a spare standing by.

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Thank you for the input! This time it didn't break at the threads. It broke approximately half an inch further back, at the start of the recess.
Aparently some carriers also brake at the end of this recess (towards the bolt).

 

 

I've made quite a few 3 gun race guns and find that, if left unmodified,  eventually most of the bolt carriers crack on high round count guns -  especially if  the gun is tuned for birdshot, then used with 3" turkey loads, or buckshot for some match stages.  The solution that works 100% for my guns is to drill out the dimples right away before the carrier cracks.  Remove the original op rod.  I put in a brass insert, (shown in the picture) then TIG weld up the holes.  With the brass plug in place during welding,  the threads are pretty good after welding.  I clean up the threads with a tap.  I then make a titanium op rod with a stepped down end (i.e. the last few threads removed) so it seats firmly against the bottom of the threaded hole.  The load is no longer on the threads or the dimple, but directly on the carrier.   I've had no alignment issues with this technique. The Tom Cole op rods are great -  very heavy duty -  but also very heavy, hence why I prefer the titanium.  . FYI the threads are M12 x 1.25   This TIG welding technique can also be used to repair a cracked bolt carrier as well.   I've never had one I couldn't save.

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No welding. I would rather not get into an explanation of why, but I can't elaborate on it here yet. I'll let the cat out of the bag sooner or later though. My position here will change soon.

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  • 2 weeks later...

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