Some time ago I ran across steel inserts that could be used in a shotgun to fire .45 ACP, 9mm, even 7.62x39...basicaly a chamber made to fit like a shotgun shell.

Well, I got to looking at my Saiga project gun lastnight and I was wondering...

Could one have a rifled sub-caliber barrel insert made to fit inside the shotgun barrel and fire pistol cal ammo? If you had a locking device at the muzzle end to anchor it into place, then you would just have to swap bolts out and use either a magwell adaptor or modified magazines.

My Cobray's bolt and spring are a lot heavier than my Saiga's, so even without the use of the Saiga's gas system, could the system work on a purely blow-back principal, or am I dreaming a little too hard here?

You are dreaming too hard.

First, your barrel insert idea is overly complicated.  Shotgun barrels are so easily removeable that you might as well make a whole new barrel to drop in, rather than a chamber insert.  What I don't understand is how you would get any accuracy at all by shooting a 9mm bullet out of a chamber insert into a 12 gauge barrel, which is of such a larger diameter that it wouldn't direct the bullet's path at all.  Plus, gas would be escaping from around the bullet in every direction, causing catastrophic loss of velocity--you'd be lucky if the bullet actually came out of the barrel at all.  There are many other good reasons why guns have rifled barrels that actually fit around the bullet.

Second, how exactly would you modify a 5 round 12 gauge magazine to reliably feed 9mm ammo?  What would have to be done with the follower and feed lips?  You'd need a completely different bolt face for each caliber, plus a different extractor design, and possibly different firing pin protrusion amounts.  Perhaps not impossible, but if you actually got it to work you'd be the Rube Goldberg of our century.

Finally, a blow back system is a blow back system and a gas system is a gas system.  When an AR15 jams up because of a gas system problem, you fix the gas system, it won't magically work again just because you told the same gun that it should work on a blowback principle.  They are not the same system; put another way, if a .223 doesn't have enough chamber pressure to blow back an AR15's bolt carrier without a gas system, how will a 9mm have enough chamber pressure to blow back a 12 gauge Saiga's bolt carrier (which weighs alot more)?

Keep dreaming, and keep reading more about how guns actually work, and you'll eventually come up with something cool.

Quoted: You are dreaming too hard.

Perhapse, but you've missunderstood some things first-

First, your barrel insert idea is overly complicated.  Shotgun barrels are so easily removeable that you might as well make a whole new barrel to drop in, rather than a chamber insert.

Um, I'm working on a SAIGA here, not a standard tube mag pump. If you're not familiar with the breed check out www.saiga-12.com. The barrel is quite fixed.

What I don't understand is how you would get any accuracy at all by shooting a 9mm bullet out of a chamber insert into a 12 gauge barrel, which is of such a larger diameter that it wouldn't direct the bullet's path at all....(snip)

 

While I described that as a pre-existing device, if you go back and read my question again,  you'll see that I'm not just talking about a chamber, but an entire full leignth rifled barrel insert that will act as a sleeve in the shotgun, full leignth. To put it this way- a full sized 9mm barrel that will slip into a shotgun barrel.




Second, how exactly would you modify a 5 round 12 gauge magazine to reliably feed 9mm ammo?
What would have to be done with the follower and feed lips?


Once again if you read my initial post all the way through, you'll see that I mentioned a magazine well adaptor, or a modified existing magazine. Ever seen a 9mm AR15? There are two ways to tackle using a 9mm magazine in a well for a .223- one is to block off part of the chamber with a slip in piece that locks in like a .223 magazine, and has its own catch for the smaller-size 9mm magazine, allowing the use of a STEN or similar mag. The other method is to take a STEN mag and perminantly modify it with a block in the rear and a modified catch in front to fit in the AR magazine well. There is no reason why these two methods wouldnt work in any other clipfed weapon. One could cut a Saiga 5rnd magazine off right under the reenforcement ribbing on top, and use that shell as a mounting point for a 9mm magazine, either perminantly or as a magwell adaptor with its own catch. The maglips on the original magazine would then become superflous and could be altered or removed to allow the 9mm magazine to sit properly in the action.  


 You'd need a completely different bolt face for each caliber, plus a different extractor design, and possibly different firing pin protrusion amounts.  


One could modify a replacement 12-ga bolthead for this purpose, about $10 through EAA. Thats the cool thing about the Saiga, the bolthead is a seperate piece. It'd probably just be as easy and cheap to replace the whole bolt to make the switch-out easier and faster. The nice thing about the AK design is the bolt is a minor part cost and size wise, so having a different bolt is vastly cheaper than having one on a conventional shotgun. As for the firing pin, this is something I didnt consider, but I dont see why it would be a big issue. If you could mill the bolthead down so the rim sat back a little further into the bolt face, then the firing pin would sit out further anyhow. (Shotgun primers are notoriously soft and require a weaker tap)


Perhaps not impossible, but if you actually got it to work you'd be the Rube Goldberg of our century.


Once again, I'm not sure your right here if you go back and see what I'm talking about in the first place. I dont see the kit any more difficult to produce or employ then a Ciner .22lr kit avaliable for DOZENS of common small arms.


Finally, a blow back system is a blow back system and a gas system is a gas system.  When an AR15 jams up because of a gas system problem, you fix the gas system, it won't magically work again just because you told the same gun that it should work on a blowback principle.  They are not the same system; put another way, if a .223 doesn't have enough chamber pressure to blow back an AR15's bolt carrier without a gas system, how will a 9mm have enough chamber pressure to blow back a 12 gauge Saiga's bolt carrier (which weighs alot more)?

Ok, here's the thing though, the force excerted on cartridge in my Cobray 9mm is HEAVIER than the force the Saiga bolt puts on a cartridge in the Saiga barrel. Even with my gas system shut off, my shotgun cycles at least some. Then wouldnt it be possible just to swap out the easily replacable return spring in the action, and allow the thing to cycle the whole way with the same impulse.

And finaly, does the 9mm realy exert less PSI on the chamber of the weapon than a 12-ga 3&1/4" shell? I was always under the impression that shotgun shells were VERY low pressure...

The best way to go about the "insert" is to simply use a piece of barrel blank, contour it to resemble a hull of the particular gauge you intend to sub-cal, and leave some length to the insert to provide a length of rifling inside the shotgun barrel, say maybe a .650" OD on the barrel forward of the false hull.

Be kinda funny to have a "break open" shotgun that spits out bullets, maybe 308, 30-06, or whatever chamber you choose.

It'd be a hell of a cheap way to do a double gun :)

The weapon I'm using it in however is a prototype entry/SWAT gun built on an Saiga 12ga, a semi-auto  box mag fed gun based on the AK47. I've worked up quite a prototype, but I think the ability for smaller departments to have an inexpensive gun like mine that can DOUBLE as a subgun would be worth its weight in gold.