Anyone convert a 12 gauge o/u to combo gun?

D

Don

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Brother wants a 12 guage over a .260 Remington combo gun, which are pretty hard to come by at a reasonable price here in the U.S..

Since availability at a reasonable price is difficult, I am thinking about stuffing a take-off .260
Remington barrel into the bottom barrel of a field grade 12 gauge o/u, alter extractor, add sight
bases, and mount sights.

Any particular mfg. of shotgun preferable over another from a pressure handling standpoint? I
would like to stick to lower end types to keep costs down.

Any tips on successfully completing this project?...............Don
 
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I'm no metallurgest but it seems a tad risky. A 12 gauge chamber is .8 inch diameter or thereabouts which isn't leaving all that much barrel for a cartridge with a base diameter of around .5 inch. Maybe with a snug fit you'd gain hoop strength from the shotgun barrel, but I'm not at all sure that I'd want to be standing alongside one going off.
 
Don,

I haven't done this specific job, but have worked with a lot of drillings in the past. I have cut the shotgun barrels off, bored out the action stubs and sleeved new barrels in place in drillings and have also built insert barrels for them. Lots of work.

You should be able to do this, but the safest way is to use a barrel insert which contains all the pressure of the cartridge on its own. You can open up the inside of the shotgun barrel to make more room for barrel thickness if you wish, but you might have enough without. I used to run hoop stress calculations before I did this kind of thing and you will find that barrels don't have to be too thick to be safe at normal pressures - most are highly overbuilt to prevent idiots from blowing up guns. I believe (from fading memory) that .030" wall thickness or so at 12 ga diameter will hold 20,000 psi or so, making a barrel with walls of .200 thick should be able to hold most high power rifle cartridges with a reasonable margin of error, but run your own calculations and talk to some other engineers before you take the plunge.

Couple of things - you might be able to get an insert barrel already made by folks in Europe. You might not be able to get 260 Rem, but they may have something close enough (6.5 x 55). The Europeans are way ahead of us on using such devices and they have already worked out the technology as to how to fit these to regular shotgun chamber/barrels so you can remove or install the barrel as suits your fancy. Also, don't do this with a cheap shotgun. My experience with the low price point guns is that they are made of rather soft steel and they will stretch and peen when stressed. A 260 Remington cartridge will stress the action some, as it operates at 4 times the pressure of a 12 ga shell, but it has less base area, so back thrust is not 4 times as much. Still, hardened hinge pins/trunnions and a Greener cross bolt or other action bolting system of merit is advisable. Browning, Beretta, Ruger, yes - Most guns built in Brazil, Turkey, Russia or China - No. You may have to reduce firing pin diameter.

Anyway, these kinds of projects are a lot of fun. Just make sure you are doing things safely. I would be happy to hear what you decide to do.

Scott
 
I've thought about doing the same thing.

A friend if mine asked me to explore the idea, with a 12 gage for one barrel and a .270 underneath for a specialized deer rifle to be used when driving deer.

Here are my thoughts.

I was thinking of machining a cartridge that was the same shape and size as a 12 gage shell, but using a .270 reamer to ream it out. The barrel would be screwed into the shell and the whole arrangement would be tensioned by using the choke threads at the end of the barrel.

Of course, the o.d. of the barrel would have to be threaded into an adapter that fit the choke threads. A simple slot arrangement like a choke uses could be used to spin the adapter and tension it in the barrel.

The whole thing would be removable, and if the tolerances were held nice and tight I think it could be fairly accurate.

I haven't done it yet, but I don't see why it wouldn't work. You could have the best of both worlds and yet it would be easy to remove.
 
Did some research...

Some budget "combination guns". (Yes, that's the correct term for them.)

Savage 24 series. Discontinued, but once were available in .308/12 gauge. About $700 used.

CZ 584. Available in calibers up to 30-06/12 gauge. Just under $700. One possible source is http://www.floridagunworks.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=FG&Product_Code=423&Category_Code=R+CG A review can be seen at http://www.gunsreview.com/shotguns/cz/cz584.html

Brno 802. Apparently current production, with a price tag of ~$2000. Available in .243, .308, and 30-06. See http://www.czub.cz/en/catalog/253-shotguns-brno-rifles/OUZBR/BO_802.aspx Found a 12 gauge/.308 Winchester combo online at http://www.cabelas.com/gun-inventory---hazelwood---european-sg---1463826-czbrno12308-haz.shtml for $1600.

Hope this helps.

Asa
 
Insert barrel makers in Europe are: Kerner, Kargl, Krieghoff, Zimmerman Rasant, Jung Tornado, Keller and Simmann, Keppler, etc. They mostly mimic a 12 ga shell at the rear (per BobB's thoughts) but also have an adjustable bushing at the front to help adjust point of impact. They can fit inside 12 ga barrels without problem, but note that larger calibers must be put only into a strong, well fitted action because of the back thrust. Given the weak dollar, buying a used combination gun might be cheaper than buying a proper European insert barrel or modifying a suitable shotgun.

If you have more time than money and have the machine tool skills, there is no reason not to copy the European designs and make the rifle barrel insert to fit the shotgun of your choice. I post this just to keep you from reinventing the wheel....

Scott
 
Thanks for all the feedback.

I have made contact with many of the listed sources and most are no longer stocking combination guns, don"t know if this is a bad economy thing and low demand type items have been dropped. Tikka also makes a field grade combo gun but seems to be very difficult to find in the U.S., although accessible in Australia and Europe.

http://www.doublegunhq.com/marocchigallery/finn.htm

My train of thought follows Bob's very closely and I would also like to use the choke threads to tension lock the rifle barrel to the outer shotgun barrel tube, except with one small addition, which would be a slight excentric barrel nut trunnion which would allow for the regulation of this rifle barrel in relation to the 12 gauge..............Don
 
I have saw CZ-12 ga.`s side by sides converted to large caliber centerfires....no choke tube reliance..... .0005" press with muzzle adjustment band.
iron sited african style guns..... I shot a .404? Jefferies..... I hit a gallon milk jug at 50 yds... first shot...???
 
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