Mark IV Series 70 Colt

It was probably a rare phenomena, but a reputable and fairly well known 1911 gunsmith I've spoken to has seen a few busted ones over the last 30 some odd years of his career.

It certainly wouldn't stop me from buying one, though I recently picked up one of the new repro series 70s that doesn't have the collet bushing. As for accuracy, a properly fitted standard bushing will produce accuracy at least as good as the collet. If your accuracy fell off by switching to a solid bushing, it may not be fitted quite right.

Back when I was in the business, I did see some broken ones. It's one of those things that gets way overblown though and I wouldn't let it keep me from owning one. I never really saw much difference in accuracy between those and the solid bushings.

I had one break on one of my series 70s, no idea how many rounds were through the gun before it happened, but it happened and I replaced it with another one.

jad0110 said:

If your accuracy fell off by switching to a solid bushing, it may not be fitted quite right.

Click to expand...

Exactly

The finger busing broke on my 1980ish vintage Colt Mk IV Series 70. Colt replaced it with another finger bushing.

Ultimately, I replaced it with a solid bushing.

Actually, the Colt barrel and bushing were replaced with a Bar-Sto 38-45 Clerke barrel and the Colt barrel found it its way into a Thompson M1911 with a solid bushing.

I had two Series 70 Colts with the collet bushing and after a couple of years I had begun to think that the stories of them breaking was just a myth. Then, within a six month period, both broke. Of course I replaced them with solid bushings.

They can break. A solid bushing will not. It was an attempt by Colt to save money by dropping in a bushing that would give better accuracy than a loose, drop in solid bushing. Sloppy tolerances on slides and barrels can result in one of the fingers breaking off if the slide fit is too tight. I would prefer a solid bushing every time. Even if it's loose. A properly fitted solid bushing is better in every way. If you send your barrel and slide dimensions to EGW they will turn you a solid match bushing that will be a near perfect fit.

kBob- What kind of accuracy difference have you seen between the two different bushings? What distance are you shooting?

My 1976 Colt never broke its collet bushing but after hearing the stories I fitted a standard bushing after about ten years. Accuracy remained about the same so I never went back. The collet bushing lives in the original Colt cardboard box.

No first hand knowledge of any problems with them. I did read a lot of the stories about collet bushings breaking but never experienced it myself nor did I hear of any problems with Series 70 bushings in guns that a lot of my friends had. I think Bar-Sto also designed a collet bushing for their barrels but had a larger, more solid finger portion on the bottom of the bushing with two other fingers providing additional tension on the barrel.

I have repaired three of them over the years.

Two of them I could get the slide off without doing any damage.

The other one had the broken collet finger wedged between the slide and barrel and I had to beat the slide off with a rawhide mallet.

It scared both the inside of the slide and outside of the barrel pretty bad getting it off.

If I had one, I would change it to a fitted solid match bushing without even thinking twice about it.

Some of them never broke, and may never.
But the ones that did break caused Colt to stop using them after a relatively short time in gun design years.

rc

If you want your old accuracy back just find a gunsmith that can fit up an undersize Match Grade solid bushing to your gun.
I never saw a broken collet bushing but I have seen plenty of Series 70s with chewed up barrel ends, slide fronts and the bushings themselves from the repeated crush fitting needed to get them back into place.

I have...but like all failures, there are usually reasons for it.

The Series 70 Collet bushing and barrel was a sound system, and it worked well. The problem came not from the design itself, but from incorrect disassembly technique. The clue is in the way that it functioned...literally using the barrel to wedge the bushing tightly against the slide bore, and at the same time, being wedged against the fingers that made the bushing bore.

Most people used a hammer to tap the bushing...or a wrench to twist it into the takedown position. That places torque stresses on the fingers that they didn't hold up well under. The sharp corners led to small cracks that eventually led to bigger cracks that eventually led to failure.

Backing the slide up a half inch frees the bushing and allows it to be turned easily. If only Colt had included that simple instruction in the owners' manuals...

But, what's done is done.

I believe that Colt did instruct users to slightly retract the slide before turning the collet bushing. IIRC, the collet bushing barrels had a gradual taper from the muzzle down to about an inch behind it. Never did have an issue with mine.

1911Tuner said:

I have...but like all failures, there are usually reasons for it.

The Series 70 Collet bushing and barrel was a sound system, and it worked well. The problem came not from the design itself, but from incorrect disassembly technique....

Backing the slide up a half inch frees the bushing and allows it to be turned easily. If only Colt had included that simple instruction in the owners' manuals...

But, what's done is done.

Click to expand...

I've long lost my manual from 1976 but I believe it did tell you to press the slide back 1/2" to turn the collet bushing. And that you shouldn't remove the bushing from the barrel. Can't be sure, maybe I read that in a gun magazine but I gained that knowledge in time for the very first field strip.

1911Tuner
Quentin

It seems Colt did mention it in their manual for the Colt Government Model Mk.IV/Series 70. On Page 24, Stripping for Cleaning:

Step 3.-Push slide back about one quarter inch, press down on recoil spring plug (located just below muzzle) and at the same time rotate barrel bushing clockwise about 1/4 turn; this will free plug and recoil spring. Keep pressure on plug to prevent it being ejected by the spring, then allow plug and spring to gradually extend out of the slide (See Figure 6).

Step 4.-Rotate plug counterclockwise and remove spring.

Step 5.-Cock hammer by pulling back on hammer spur.

Step 6.-Pull slide to rear until lug on slide stop is opposite disassembly notch (See Figure 7) and push rounded end of pin of slide stop (on right of receiver) inward and through receiver to disengage slide stop from slide.

Step 7.-Lift out slide stop (See Figure 7).

Step 8.-Pull receiver to the rear and off the slide.

Step 9. Lift recoil spring and guide and pull them rearward out of the slide (See Figure 8).

Step 10.-Turn barrel bushing counter-clockwise, push barrel bushing forward until bushing is clear of slide, then remove bushing from barrel.

Or just have a solid bushing fitted and forget about it.

Good to know that Colt did include those instructions at some point...probably after several were returned under warranty. I've looked through several Series 70 owners' manuals and haven't seen it.

Even so...how many people actually take the time to read a manual carefully from cover to cover?

1911Tuner said:

Good to know that Colt did include those instructions at some point...probably after several were returned under warranty. I've looked through several Series 70 owners' manuals and haven't seen it.

Even so...how many people actually take the time to read a manual carefully from cover to cover?

Click to expand...

Owners manual?!?

I read the remarks about incorrect dissassembly being a cause and that could very well be, but that was not the cause of the breakage of my two bushings. I always slightly retracted the slide before turning the bushing. If the collet bushing was better, Colt (and others) would still be using it.

Kuhnhausens 1911 shop manual, Volumn 1, clearly describes how and why collet bushing break.

It has nothing to do with how you take the gun apart, although no type of fitted bushing should be turned with the slide in battery.

The reason collet bushings break is because they were not fitted with enough slide clearance at the factory when the barrel knot pushes them out at full lock-up.

If they are too tight, there is not enough room for the fingers to expand into the slide so they have to flex in the middle.
And they are not designed to flex in the middle.

On page 43, you will find specific instructions on how to check slide clearance on the bushing fingers.

And how to correct it if it is wrong.

With all that known?

I still change them to a solid match bushing given the option.

Rc

Colt Called them Accurizer Bushings. At less cost to Colt than hand fitting solid bushings the guns got a boost in accuracy. Most shooters noted and appreciated this.

Kuhnhausen is correct on the down side of them. Many were also damaged by incorrect dis-assembly of the guns as mentioned earlier.

Colt borrowed the idea from Bar-Sto.

Bar-Sto barrels was the first to introduce the collet bushing. They made their own version that operated differently from what Colt later introduced. They had a different patent. The Colt was a draw type collet, the Bar-Sto a centering collet.

The Bar-Sto design used the springiness of the fingers against the barrel to center the two and provide for a tight fit.

The Colt collet worked by centering the barrel in relation to the slide and closed for a tight fit like a drill bit in a chuck.

Colt stopped making them because of breakage and the cost, while less expensive than hand fitting they were more expensive to make than standard bushings.

Bar-Sto quit making them due to breakage from people removing them incorrectly. So they said back in the day.

tipoc