Almost as soon as Colt introduced the Series 80 pistols, they began to be denigrated by the purists, and all the pre-Series 80s…whether they were built in 1912 or 1982…were to become known as “Series 70”  guns…even the pistols not made by Colt.  Now, it seems that even Colt has taken to using the term to let the buyer know that there isn’t a Series 80 firing system in place.

In 1973, a Colt designer came up with an ingenious way to enhance the out of box accuracy by tightening up the muzzle end of the barrel fit with the slide without the need for tedious hand fitting.  It was a slick piece of engineering and it worked very well.  If a buyer also happened to get a pistol with a decent fit at the rear, his Government Model or Gold Cup was capable of sub-2-inch groups at 50 yards with good ammunition, and I’ve seen a few that would nearly break the one-inch barrier…at the time, the holy grail of match grade 1911s.

It consisted of a long, four-fingered spring tempered “collet” bushing with inverse ridges near the rear along with a new barrel that had an enlarged section starting about an inch behind the muzzle.  As the slide went to full battery, the larger barrel section entered the ridged section of the bushing which caused the bushing to be forced into hard contact with the slide…and in turn, caused the bushing to grip the barrel tightly.  The result was a fit that rivaled the most careful hand fitting.

Prior to this new innovation, all barrels were pretty much concentric in diameter from in front of the 3rd lug to the muzzle, and the bushing bore had to be several thousandths larger than the barrel to allow the barrel to drop when it linked down.  Moreover, the bushing to slide clearance had to be generous enough to allow it to be easily turned for field stripping, as dictated by the old US Army requirements.  This led to fairly generous play at the muzzle of the gun.

It turned out to be the only real improvement over Browning’s original concept, but it wasn’t without its problems.  Shooters started reporting broken bushing fingers, often while the gun was in use and the results ranged from simply jamming up the gun solidly to actual damage…and shooters started replacing the bushings with the original,  solid ones.

As it turned out, the broken fingers weren’t a design flaw, but rather a mistake in the field stripping process.  1911 owners had become accustomed to turning the bushings with the slide in full battery, and the tight collet bushings required a bushing wrench to turn with the slide in that position.  Some few even resorted to using a plastic mallet to tap the bushing.  That practice places torque stresses on the bushings, and the sharp corners eventually gave way and started to fracture.  From there, it was a short time until a finger or fingers failed.

The early owners’ manuals didn’t include the instruction to back the slide up a half-inch before attempting to turn the bushing and to never remove the bushing from the barrel…and although the later ones did, the die was cast.  Horror stories of failed bushings spread, and the owners of Series 70 pistols decided to trade their enhanced accuracy for a trouble-free gun…and the Series 70 accurizer system faded away.

The upside is that the accurizer barrel design led to what we now see as commonplace, with an enlarged muzzle section…a lot shorter than the original…that provides less play between the barrel and bushing while allowing for adequate linkdown clearance…and better mechanical accuracy than its pre-Series 70 predecessors.    The only modern 1911 that I’m aware of that still had the concentric barrel diameter was the Norinco.  Due to import bans, I haven’t seen a recent production Norinco, so I’m assuming that hasn’t changed.  I could be wrong.

The best part of the Series 70 system was that the barrels and bushings could be purchased from Colt for a couple of years as a drop-in upgrade for the pre-70 pistols, but few owners/shooters took advantage of it.   In all my years and all the 1911s I’ve had my hands in, I’ve only seen two pre-70 pistols with the Accurizer system…an early Gold Cup and a Remington Rand.

For the record, there were no Series 70 Commanders because they were never offered with an accurizer barrel and collet barrel bushing. The Commanders without the firing pin safety are known as Pre Series 80.

3 thoughts on “1911 School: Series 70”
  1. John,

    Thanks for the article…but I’m a bit confused. In the early 90’s I bought a NIB Colt Series 70 MKIV in 9mm. I think 9mm was pretty rare for a Colt 1911 style frame back then. As my memory serves, the only other Colt attempt at a 9mm back then was the 9mm Double Eagle released towards the end of 1989 in an attempt to ‘beat’ the foreign 9mm’s to the US market.

    You state ” In all my years and all the 1911s I’ve had my hands in, I’ve only seen two pre-70 pistols with the Accurizer system…an early Gold Cup and a Remington Rand.”

    So if I understand you correctly, is my 9mm “collet bushing” Series 70 MKIV NOT a Series 70? I no longer use the collet bushing and to remedy any looseness from a standard Colt bushing, I use a custom drilled bushing from EGW (Evolution Gun Works) who made me one for around $30 and it includes the correct geometry for the barrel link tilt and lockup.

  2. If the pistol is marked Series 70 and it was originally equipped with the collet bushing and accurizer barrel…it’s a Series 70.

  3. And not every pre-series 80s is called series 70.

    The series 70s are not the same, in several aspects, as the pre-series 70 1911s, just like 1911s, government models, and 1911 A1 are not the same.

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