300-600 USD
SKS receivers are milled. AK receivers can be stamped or milled.
Adapter for what, exactly? You could be trying to install a different buttstock type, Picatinny rails, or a number of other accessories. Other than some sort of unspecified adapter, you really don't tell us what it is you're trying to do.
The barrel has deep grooves milled into the outside of the barrel. Called flutes, the grooves reduce the weight of the barrel, yet leave it a stiff barrel with very good accuracy.
$1000 - 1500 USD depending on model milled or stamped receiver, fixed or folding stock.
They were milled as part of the barrel
The receiver and receiver cover are typically made of stamped steel (Though older/higher quality AKs are made of milled steel), with solid steel barrels. In under-folding AK47s the stocks are also made of stamped steel. In standard AK47s the stock and hand guard are made of wood. In more modern AK47s the pistols grips are made of plastic, while in classic AKs they were typically wood. Current-day AKs (The AK74 series) use the same barrel and receiver materials, with plastic stocks, handguards, and pistol grip.
The original factory barrel will have the name Winchester and the chambering of the gun stamped into it.The color is another tell, the color on the chamber should match the barrel exactly.Look at the joint between the barrel and the chamber, can you see any bare metal at the end of the barrel?A replacement will have to have had the threaded end of the barrel milled after it was blued to get it to fit right.
The root word of milled is mill
If you're looking for the side folder, the regular wood stock should be pretty much the same as any other AK - two screws inside the receiver hold the stock in place. Side folders with a mount which attaches into those same screws are available, and you can find them sold at any gun show. If you want the underfolding stock, that one actually requires holes to be drilled into the receiver. If your stock is affixed in a different manner, feel free to send photos via email (address is in my bio page), so I can get a clearer picture of what we're working with here.
When a coin is milled it means that the coin was made using machines instead of hand made. Milled coins have ridges outlining the coin. The dime and the quarter are milled.
Nothing is added to make a coin milled. Milled means it been struck by a machine.
Corn bread is made with flour mixed with milled corn.