QUOTE: "...Does anyone have anything official saying that Winchester used the sintering process (or any other process) to make those receivers?..."
James K, though the following isn't from the "horse's mouth" (i.e., Winchester), I did find this in Robert C. Renneberg's book, Winchester Model 94; A Century of Craftsmanship", 2nd Edition:
"...There is an ongoing dispute over the exact serial number of both the last production second model receiver (Pre-64) and the first third model receiver (Post-64), but second models most assuredly end near or at the very early 2,600,298 range and the third models were introduced somewhere near 2, 700,000. The rumored last Pre-64 Model 94 assembled is number 2,600,298. The gap between this number and the very earliest known Post-64s is so far unexplained.
"The problem is not distinguishing a Pre-64 from a Post-64. The difference is glaringly apparent. The problem is finding very high numbered (near 2.6 million) Pre-64 receivers to examine...A gap of about 100,000 pieces in a sequential serial system is certainly mysterious and quite worthy of further investigation.
"...Introduced after a few years of development was the new 'cost effective' third model (Post-64).
"This new model was such a blow to Winchester fanciers, such a departure from the quality of even the worst example of the previous design, so disappointing in appearance and feel, that sales plummeted dramatically.
"It rattled when you shook it. The action was an abomination with a flimsy sheet steel stamping serving as the carrier, and the receiver itself didn't take kindly to the bluing process. Even the fit and finish of the wood was terrible-on a par with the rest of the gun.
"Equating this degree of quality with that of other products coming from certain areas of the Orient, the Model 94 became derisively known as the 'Japanese" Winchester. Not altogether surprising, many people were convinced that the gun really was being made in Japan. It was NOT.
"The receiver itself was now a casting, an investment casting. The material from which it was cast was an alloy of some kind of 'mystery metal' that not only resisted polishing, but also refused to adequately react to the bluing solution. This alloy proved to be so inhospitable to finishing that it finally had to be plated with iron just to provide a consistent medium upon which the bluing solution could react.
"...The final 'solution' was to use a black oxide finish that, while in reality was hardly more durable, but at least had a smoother, higher quality appearance.
"...By the late 60s, due to lagging sales and 'unkind' references, Winchester was forced to rethink its product. The changes begin to be noticed around the 3,400,000 serial range and these 'improved' models are characterized by a phenolic instead of a steel buttplate. Let's call this receiver style, 3a. These guns, while not up to the Pre-64 standards, were nevertheless vast improvements over the immediately previous design..."
Mr. Renneberg went on to describe the design changes, finishing procedures and material compositions of the subsequent Fourth Model, Fifth Model (or 5A-Angle Eject BigBore) and Sixth Model (6A-Angle Eject, 6B-Angle Eject with Button Safety, 6C-Angle Eject with Tang Safety).