Interchangable barrels
Is There Anything 30 Cal Barrel That Is Easily Interchangeable With The 223. By Easy I Mean With Out Taking To A 'smith. I Can Change A Barrel And Bolt And Check Headspacing.
NOPE
The Remington 700 as it comes from the factory, has a barrel that is screwed into the receiver fairly tightly. To take a barrel off, you need a barrel vise, and a proper action wrench.
Remington 700 actions and barrels have the same threads. If you know what you are doing, it is possible to switch barrels. In addition to the barrel vise, and action wrench, you also have headspace guages for each calibre.
In the case of the .223 and the .308, you would also have to have two different bolts. The head diameter of the .223 is a lot smaller than the .308, and the bolt is of one piece design for the main body. There is no way you could use a .223 bolt for a .308 case without altering the front of the bolt face and the extractor.
It would be possible to use a .243, 22-250, 6.5-08, 7mm-08, 250 Savage, 338 Federal, or .358 or any short wildcat cartridge that uses the basic head diameter of the .308, but it still requires proper headspacing.
I am not aware of any .30 calibre cartridge that is based on the .223 diameter head diameter, except for some wildcat cartridges such as the 7mm TCU, 30 Apache, or .300 Whisper, or any such as these.
Another big problem would be the magazine. You would have a single shot rifle, because the .223 would not feed from the 700 short action as used for the .308. Chances are you would also have to zero the rifle each time.
With the expenses involved in buying a barrel, gunsmithing, tools, etc., it would probably cheaper to buy a second rifle. You would then have what you want--a .223 and a .308 without a lot of effort.
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