To begin an examination of the Series 70 guns, we need to fill in a bit of the background that led up to the design of the original 1911A1 pistols. They were an upgrade of the original 1911 pistols. Army Ordnance took all of the comments made by combat users of the 1911 in the years following WWI and went after corrections. Everybody seemed pleased with the pistol’s power and accuracy, but many felt that the gun was too big, had an excessive trigger reach and even pointed low. There really wasn’t a great deal they could do to make the gun smaller, but the other problems were correctable to some degree. For one thing, the Ordnance people shortened the trigger. Instead of the old, smooth-faced long trigger, they cut it back by about a quarter inch, which suited small-handed shooters much better and was still usable by the big guys. They got a little more improvement by cutting a crescent-shaped relief on each side of the frame at the rear edge of the trigger guard. This shortened the distance to the trigger. They also applied a checkered surface to the trigger face.
The pointability question was resolved by installing a completely new mainspring housing at the lower rear corner of the butt, which was arched, with more material added. This gave the shooting hand greater bearing surface, causing an admittedly muzzle-heavy pistol to angle upward. This change overcame the tendency of the gun to shoot low, particularly in close range encounters at high speed. A final modification addressed the problem of the 1911’s nasty tendency to bite the shooter’s hand. On the original 1911s, the grip safety tang was too short. This caused the fleshy web of the shooter’s hand to override it and thereby exposed the hand to a nasty bite from the spur of a fast-moving hammer. The solution was pretty simple—lengthen the tang and shorten the spur.
Beginning in 1924, the changes were incorporated on both GI and commercial pistols and continue to present day. In the early 1970s, Colt introduced a new variation of the 1911A1 pistol. This was the Series 70 Model, which incorporated a major change calculated to improve accuracy. It was a collet style barrel bushing with four flexible fingers that centered the barrel perfectly in relation to the slide. It worked very well, but the increasingly powerful ammunition developed in this same period was hard on the system and the factory had severe warranty problems when one or more of the fingers broke. With little fanfare, Colt dropped the collet bushing, leaving the Series 70 pistol different from the plain M1911A1 in nothing but markings.
Then came the Series 80, the major feature of which was a trigger-activated firing pin safety. Certain states were mandating drop safeties to prevent dropped-gun accidental discharges. Colt responded with a clever safety that drew off a bit of the trigger pressure to elevate a plunger in the slide that cleared a path for the forward movement of the firing pin. I have had considerable experience with several guns of this type. There’s not much doubt that they have an adverse impact on the traditional Colt trigger pull. However, the impact is not unbearable, particularly if a competent pistolsmith touches it up. Despite these facts, the firing pin safety was something that was—and still is—heavily criticized more often than not. Most of the new brands of 1911 pistols have some form of them. To avoid the Series 80 safety, most shooters started looking for a good Series 70 or earlier pistol, since Colt had dropped them with introduction of the 80 Series.