All guns are a compromise of the manufacturing methods that were available at the time and you can watch the evolution of how the designs evolved to make them more economical to produce based on current technology. If we start with a mauser 98 action you see that compared to mid 1900's designs it is fairy complex. They were forged into shape with the bottom of the receiver machined flat. Note the recoil lug machined into the bottom, the extended tang on the back, the machining cuts for the fixed extractor in the side. This was an expensive and time consuming part to make. Forging was used because at the time forging a part into near net shape was a lot more cost effective than machining. These types of designs are dominant up through WW2.
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In the post war consumer era the technology changed and we saw an evolution toward machined billet parts as a result of massive improvements in machining and cutting tools from ww2. The next evolution of bolt action rifles are designs like the remington 721 and 700 and savage 110. These reciever designs are basically tubes machined out of bar stock because it was cheaper to just machine them out of a chunk of steel on a lathe than to forge them. To make it simpler and faster to produce the ejector is now just a spring loaded plunger in the bolt head and the recoil lug is a separate piece that sandwiches between the barrel and receiver to save machining time. Another thing is now you have guns that did not come with any sights on them but they didn't put any optics mounting on them either other than drilling the holes for mounts to screw on because its a lot cheaper to make the mounts separately. There was no CNC or automated tool changes in this era so every machining operation would be done on a different machine. Because of this there is an effort to reduce the number of machining cuts that have to be made to a minimum. The howa that you mentioned is definitely part of this era of guns designed between WW2 and like the 1990's.
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Next you have guns that were specifically designed to be made on a CNC machine. Once you are producing the receiver on a 4 or 5 axis CNC machine with an automated tool changer, now you can make 10, 20, 30, or more machining cuts in the same fixture. Previously if you wanted to add another 4 machining cuts to a design you had to add 4 more milling machines to the production line. Now its just a programming change and adding another tool to the tool holder. Now you can just mill the scope mounting rail and recoil lugs integral to the receiver and it just takes an extra 3 minutes of machine time. Since you are starting with a block of metal and milling it in a vertical mill rather than a lathe it doesn't need to be round anymore either so you can do flat tops and sides or add scallop cuts or whatever. Good examples of this would be the Tikka T3, or an accuracy international receiver. These are still following the paradigm of a barreled action sitting on top of a stock, but they were designed from the start to be cnc machined instead of just using cnc machines to make a 1950's design.
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The next evolution is rifles like the sig cross where the receiver, is no longer bolted on top of the chassis, but the receiver itself is the chassis. In the case of the sig, they use a barrel extension and barrel nut similar to an AR15, so the locking lugs are in the barrel rather than the receiver meaning you can make the receiver out of aluminum or magnesium or polymer. In this type of design the head space is set by whoever made the barrel, so just like an AR15 you could have a platform where any untrained person could order all the parts online and assemble them all together without any gun smithing knowledge into a functional and accurate rifle.
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