Double rifle machined from one block of steel

[grey_pilgrim]

So I was thinking about double rifles, and about how one difficulty in making them was in getting the two barrels to shoot to point of aim. Then I wondered if one could take a block of steel, machine two bores into the steel, attach it to an action, and voila - no regulation of barrels needed.

After a quick google, I'm not the first one to have this idea (though my quick skim suggests that the patent is more about how to make the bores have a convergence point): https://patents.google.com/patent/US7707761 . And now you can buy one of their shotguns for ~38k for the 'standard price'.

But my question is:
Why don't we see more double rifles machined out of an elongated block of steel?

One reason I can think of is that once you've machined a double rifle barrel out of one solid block - that's it and you can't make any changes. If there's a small error in the machining, you've basically just made a hunk of scrap with two barrels that shoot to very different places.

If you machine two barrels and regulate them after the fact, you can regulate them, shoot to test, and then change as needed. But I have no idea as to the tolerances required for double rifle barrels and if a CNC/Lathe could be precise enough to get the barrels drilled in the same place.

[Mobuck]

As soon as one barrel is shot a couple of times and begins to heat up, the POI will drift.

[kozak6]

Joseph Whitworth patented that sort of thing in the 1850's. Reportedly, high costs and material difficulties kept it from being worthwhile.

Longthorne makes shotguns like that, and maybe safari rifles eventually. Costs $20k-30k.

[FITASC]

Longthorne in England makes their shotgun barrels from one piece:

How is this achieved, one might ask, it’s all in the barrel technology. Our barrels are manufactured from a solid block of steel, including the mono block which enables us to manufacture perfectly straight barrels without the distortion and metal softening problems of many conventionally made barrels. This same cutting edge technology also ensures that our guns have a consistent point of aim and improved pattern over a greater distance.

https://www.longthorneguns.com/about/

[44 AMP]

One reason I can think of is that once you've machined a double rifle barrel out of one solid block - that's it and you can't make any changes. If there's a small error in the machining, you've basically just made a hunk of scrap with two barrels that shoot to very different places.

This is pretty much it. No matter how well you make the bores so they "point" to the same spot at a given distance, this is not a guarantee that a load will SHOOT to that same point. There may not be any "error" in the boring, and you can still have the load not shooting "together". Without being able to adjust the barrels, you're done, and you get what you got.

The traditional method using wedges between the barrels is time and labor intensive (which is why its so expensive) but it does work. And, its necessary, because only actual shooting of the load going to be used will show what it actually does.

Considering that the usual use for heavy caliber double rifles (and rare as those are, light caliber double rifles are even more rare) having the barrels shoot the same load to very nearly the same point of impact at close range to stop dangerous game, and the cost of such guns (and they were NEVER cheap, even back when they were in more common use), the customer wants more than "we engineered it to work" they want real world PROOF it does work the way expected.

Double shotguns are regulated as well, but because of the nature of the beast, (shotgun pattern at range) the work needed to get both barrels to the same point of aim is often less than it takes to get a double rifle properly regulated.

[FITASC]

light caliber double rifles are even more rare

Peter Hofer's Hummingbird double rifle weighs 2.2#; 1KG and is chambered for either the 17HMR or 22 Hornet.

[Jim Watson]

Ol' Karl comes up every now and then.
I wonder how many SolidSolid guns he has built.

I recall an old Shotgun News ad for a Steyr double rifle with one piece barrels. Some light caliber, a 6.5, I think.

I am kind of confused by the Longthorne stuff. Have they redefined "monoblock?" I have not seen a double gun with parallel bores and wonder how it is made to shoot parallel. Ray Ordorica says he has a double rifle that shoots parallel, barrel group centers are the same distance apart at all ranges, none of this conventional wisdom converging lines of fire.

[precision_shooter]

As an amateur knife maker, It’s not just machining errors that would scrap the barrels, but also any imperfections in the steel that can’t be seen before machining. Knife makers often have to scrap a piece of steel because it has imperfections hidden within that only reveal themselves once you start forging, grinding, and otherwise machining the material. Could be quite costly on a piece of high carbon steel that size.

[Art Eatman]

A guy from Kevin's of Tallahassee told me that a re-sale of a Hummingbird was for over a million dollars...

Hofer told me that a plain-vanilla Hummingbird would cost me around $125,000.

[FITASC]

Hofer's stuff is among the finest ever made, and the stuff dream guns are made of. C'mon Powerball!