The Series 70 MK IV came with a collet barrel bushing and a special barrel. When the gun was in battery, the collet held the barrel tightly in place. This collet bushing was not used on any other model. The rest of the Series 70 parts were conventional except the highly polished blue slide/frame or electroless nickle finish.
Series 80s had quite a few changes including the introduction of an all stainless steel gun (also available in the Combat Commander). They made the "Enhanced" models that had even more changes. All Series 80s have a firing pin interrupt plunger in the slide. This requires two trigger activated parts, one on the sear pin, one on the hammer pin. The grip safety tab was ground thinner to clear the series 80 parts. The firing pin and extractor were modified to accommodate the firing pin interrupt device. The front sight changed from a thin to a wide tenon and later to a dovetail mount. The frame where the slide lock is located went from a "hole" to an open slot. The extraction port was enlarged. The mainspring housing was changed to plastic.
Series 80 MK IV enhanced models came with a beavertail grip safety, arched mainspring housing, wrap-around rubber grips, extended plastic trigger, skeleton hammer, 3-dot sights, a flat top slide, cutout behind the trigger guard, beveled magazine well, reshaped extraction port, 8 round magazines (2ea), and a few things I'm forgetting (13 changes in all).
Colt now makes a new Series 70 that is supposed to be like the original pre-Series 70 MK IV, basically a vanilla 1911.
