I have long had an interest in takedown rifles. Starting about 1994 when it was still possible to carry one's rifle in norma; luggae on planes. I have a duffel bag with a bottom section which was supposed to be the place to carry a gun case. Might make the duffel too heavy for flights though. Irrelevant now, as the gun case must be checked in separately now anyway. But useful for carrying a rifle "in country", hidden away in luggage when in hotels, travelling etc. Unobstrusive.

Not an expert on takedowns. But from my research various options exist.

1. Break open rifles such as single shots, doubles, drillings etc are all "takedowns" of course.

But if talking about bolt actions.

2. My takedown system is the Mauser M03 system. A number and great variety of barrels and calibres ranging from .222 to .450 calibre. The stock is not a "takedown" in terms of the forend also being detachable. Bolt head and magazines are exchangable to faciltate different chamberings/cartridges. The Mauser QD mount system is relatively reliable as well, so having a scope for each barrel works reasonably well. I do test my rifle each time I re-set a different barrel and scope just in case. The impact hgas so far been acceptable for field use without adjusting the scope.

A great benefit of some takedowns is when the "collar" is not on the action but on the barrel so the bolt locks up in the collar on the barrel. Headspace issues with time are then avoided. The Mauser M03 has this as do most modern factory takedown systems.

The Mauser M03 is relatively affordable. The reason I went with this system was when I worked out how much a Mauser 98 system set would cost me, and it was tens of thousands of dollars compared to a much lesser cost for the Mauser M03.

3. Sauer and Blaser rifles. Many European makers eg Merkel etc also offer a form of takedown modern rifle. Not shortage of current makes to look at and consider.

Some of these systems mount the scope on the barrel, probably meaning any issues with changes of zeros are less likely when changing barrels.

Another system no longer in production but available second hand was the Mauser M66.

4. Dakota used to make a M98 variant takedown with a collar attached to the barrel and the Mauser style bolt locking up in the collar on the barrel.

Some other makers may also do this on current actions/barrels.

5. Interrupted thread Mauser 98 barrel takedown. When I purchased my Whoitworth Mauser 98 in .375 H&H Mag, I intended to have it converted to a takedown rifle. Discussed this with the selling gunshop and gunsmith before buying it. When it arrived, they "decided" it wasn't a good idea. Too much wear and tear on the threads they claimed. Turned out the rifle had other problems only identified later, ie the thread on the barrel was actually cut at an angle! And the stock was made to adjust for the angled barrel! A reason I could not get the scope to zero, ie always shooting way to the left. A different gunsmith made some mount bases to align to the barrel and not the action, and also had gaps in the middle of the bases to allow the open sights to be used when the QD scope was removed. So problem solved but not as a takedown. Use it like it is, and it works well even with the issues it otherwise had.

Basically in simplistic form the threads on the barrel are either "loosened" but not interrupted to allow the barrel to be more easily unscrewed by hand. Requring full twists of the entire thread. OR grooves are cut through the thread allowing a part turn and the barrel to be removed from the action. I assume complementary grooves are cut in the action threads. The forend is cut ahead of the action, and a switch to bolt locks it in place to prevent any unwanted twisting of the thread when the bolt is not pulled back.

This system does require only chambering/cartridge choices which are complementary as to bolt head and magazine compatibility. And this assumes any feeding issues do not eventuate from different calibre and projectiles shapes and sizes.

6. Another takedown system allowed the barrel action to be relatively easily removed from the stock. Some Holland & Holland rifles and Mannlichers utilise this system. Does not allow the changing of barrels of course. But does allow a rifle to be transported in a shorter case/luggage. Of course one can does this with any bolt action rifle, remove the barreled action from the stock and carry in dismantled form. How I did it in Zimbabwe in 1994. Does require the rifle to be resighted in.

I would think many bolt action rifles could be modified to this sort of takedown system without a lot of problems by a knowledgable gunsmith.

I was keen to have a New Zealand acquaintance make a Winchester M70 into a takedown system for me, back in 1993. He converted a number of M70's for clients, I remember one in 7mm Rem Mag, .338 Winchester and .458 Winchester. I was keen for one in that choice but a .416 Taylor-Chatfield as the larger choice. Never happened. These M70's used the interrupted thread system.

Lots of choices and ideas. I strongly do prefer the locking collar on the barrel system, as then there is no wear on the threads from being unscrewed and screwed again and again, and any resultant headspace issues. Some newer Mauser 98's variants DO do this, and would be my choice. But for the tens of thousands of dollars to buy them!

There would be other threads on the NitroExpress forums on takedowns, to search and read as well.