1911 Skool: It's in the Angles

John Travis

Happy to be here
Supporting Member
Joined
Dec 22, 2016
Messages
1,005
Location
Lexington, NC or thereabouts.
The 1911 pistol...like all pistols...is full of angles. Angles everywhere! Some are apparent, some are not. With some of them, the reasons for them are also apparent. With others...not so much.

Examples are:

The grip angle, of course. The feed and barrel ramp angles which to spec are 31-31.5 degrees and 32-32.5 degrees respectively. The reasons are obvious, but some ask why the difference in the two. That's also simple. The barrel ramp aka 'throat" isn't a guide. It's a clearance.

The hammer hook angles, which aren't 90 degrees, by the way. 89 degrees is nominal. That means that when a gunsmith squares and shortens those hooks for a trigger job, he's essentially taking it out of spec, but that's an argument for another day.

Now, as any machinist/toolmaker knows, there is no such thing as a perfect dimension. There must be a +/- tolerance, and the smaller the tolerance, the more critical the nominal dimension.

i.e. The given dimension of a part with a tolerance of +/- .003 inch is less critical than the same part with a tolerance of +/- .0003 inch.

Which brings us to the mysterious angle in the pistol...the breechface angle, which is specified as 89 degrees, 8 minutes relative to the bottom surface of the center slide rail. Mysterious because there is no tolerance provided in the blueprints. None. It violates the first rule of manufacturing. There MUST be a tolerance.

I first noticed that specification in the 60s. At first, I shrugged it off, but when I began my journey into machine tools, it kept coming back. It bugged me. I couldn't shake it. There must be a tolerance...yet, here was a specification on what is arguably one of the most famous of all pistol designs...without one.

Why? Why? Why?

It can't be to match the barrel's tilt. That can vary a bit from one pistol to another for a few reasons. There would be no reason to specify such a precise dimension in order to match up with one that can have so much variation.

When faced with trying to understand a machine's operation, I mentally shrink myself down to .001 inch tall...get inside the machine...and watch the operation in slow motion over and over until I see it...until I'm satisfied that I "get" it. The reason that I do that is simple. If I can understand exactly how and why a machine functions the way it does, I can figure out how to fix it if and when it doesn't function as intended.

So, get your thinkin' caps on and give me your thoughts on this.
 
Last edited:
Hmmm...

I doubt it has anything to do with the angle in full battery, per se.

Possibly something related to barrel motion due to the fact that the barrel's breach drops as the slide moves back. JMB designed it that way for a reason, obviously.

Maybe it helps feed the ammo correctly. But then, extraction is also just as important, so that's probably a factor as well.

What's the angle when the slide is all the way back?

Now, as to why there's no tolerance listed, that beats the bejeebers out of me. Even today's manufacturing processes will have SOME variances and tolerances are critical in manufacturing controls to ensure the parts function together properly as a whole.

Maybe his 34th birthday was a really big shindig and it was at 8 pm in 1889?
 
I doubt it has anything to do with the angle in full battery, per se.
Correct.
Possibly something related to barrel motion due to the fact that the barrel's breach drops as the slide moves back.
Since per the blueprints, the face of the barrel hood isn't wedged tightly against the breechface, that isn't it. either.
Maybe it helps feed the ammo correctly.
Now, this is why I like to see you get involved with technical discussions, Chief! You have the mind for it. It's also why you'll be able to wrap your head around the answer that eluded me for so long...and it came to me by playing with two rectangular Lego pieces.

It's about feeding. Specifically...controlled feed. <----Clue!

Rather than spelling it out, I want to let you shrink yourself down to .001 inch tall and watch the feeding phase in slow motion. I'm betting that you'll nail it.

For everyone watching this one, please refrain from commenting. The Chief is on it, and I don't want the waters to get muddied.
 
Last edited:
The rim must pivot in an arc around the projectile end as it releases from the feed lips and the angle on the breech is there to control the speed as it meets the extractor?
 
Last edited:
my cap says it’s to allow for the alignment of the cartridge as it leaves the magazine tilted slightly nose up. the rim needs to get under the extractor hook without binding.
 
Which brings us to the mysterious angle in the pistol...the breechface angle, which is specified as 89 degrees, 8 minutes relative to the bottom surface of the center slide rail.
wait - I may be picturing this wrong. Which side of dead-nutz 90 is that angle? does the top of the breech face lean forward toward the muzzle or rearward?
 
Which side of dead-nutz 90 is that angle? does the top of the breech face lean forward toward the muzzle or rearward?
It's not 90. It's 89 and 8 minutes.

Looking at the left side of the slide...muzzle end pointed left...the angle is like this. \ If it were like this / the angle would be specified as 90 degrees, 52 minutes.
 
The rim must pivot in an arc around the projectile end as it releases from the feed lips and the angle on the breech is there to control the speed as it meets the ext
Close enough to give you the win for this one. Good thinkin'.

A more detailed explanation on how this works is forthcoming. I want to give Chief the opportunity to expand on his assessment.
 
ok I had that pictured wrong. before you explain, I had assumed the centerline of the bore is parallel with the slide rails. is it?
 
Is the bore maybe 52 minutes off of parallel when it's in battery?
From the original post:

It can't be to match the barrel's tilt. That can vary a bit from one pistol to another for a few reasons. There would be no reason to specify such a precise dimension in order to match up with one that can have so much variation.
 
Is there going to be an explanation of why no tolerance is given and if the exact angle is really important?
 
Is there going to be an explanation of why no tolerance is given and if the exact angle is really important?
looking at the Rio Benson prints two points are already specified on that surface with tolerances so adding a tolerance to the angle would be over constraining the part. In other words if those two points are in spec that surface must be as well.
It is likely the angle is called out to make the machinist aware it is NOT 90 degrees. Usual practice is all corners are to considered perpendicular unless otherwise specified. In this case it is so close it is very possible to overlook especially back in the days of actual blueprints made from hand drawings where the lines are fuzzy.

D2D4C892-AB32-46D0-B0A5-6F272FBDF79F.jpeg
Edit: It is very common to add “reference “ dimensions to a print to aid in clarity, aid in tool setup and part measurement. Several standards have been used, dimensions is parenthesis (X.XXX), or callout X.XXX REF or simply left without a tolerance and there is a note stating “all dimensions without tolerance are reference“ .
 
Last edited:
Is there going to be an explanation of why no tolerance is given and if the exact angle is really important?
No. I only brought that to the table to illustrate that the angle is critical. To tell the machinist to try as hard as humanly possible to hold to it. The real question is:

Why is that angle specificed to begin with? What purpose does it serve? What is it for?
 
Last edited:
From what I can see the barrel is angled relative to the slide rails and the breech face is cut to match. This would bias the barrel to 6 o’clock position on the barrel bushing so the barrel location would be more repeatable increasing accuracy.
Picture below compares a G19 and early 1911 and both show the same 6 o’clock bias.
I do not have a reliable Glock drawing so I can not confirm this.

That said there could very well be several reasons for this feature.

060FFA23-5947-4607-AF86-BCF589B59BF9.jpeg
 
From what I can see the barrel is angled relative to the slide rails and the breech face is cut to match.
Which has nothing to do with the breechface angle.

Cut/paste from the top post.

"It can't be to match the barrel's tilt. That can vary a bit from one pistol to another for a few reasons. There would be no reason to specify such a precise dimension in order to match up with one that can have so much variation."

The question isn't why there is no tolerance specified. Clearly, it would mean little with a 2 or 3 minute variation plus or minus. The precise dimension is the designer's way of talking to the machinist, telling him that he needs to strive to do his best to hold to that dimension...to not get lazy or lose focus and let it slip.

The question is: Why is there an angle in the first place? What is its purpose...its function?
What is it for?

And, this one ain't about Glocks.
 
Last edited:
Which has nothing to do with the breechface angle.

Cut/paste from the top post.

"It can't be to match the barrel's tilt. That can vary a bit from one pistol to another for a few reasons. There would be no reason to specify such a precise dimension in order to match up with one that can have so much variation."

The question isn't why there is no tolerance specified. Clearly, it would mean little with a 2 or 3 minute variation plus or minus. The precise dimension is the designer's way of talking to the machinist, telling him that he needs to strive to do his best to hold to that dimension...to not get lazy or lose focus and let it slip.

The question is: Why is there an angle in the first place? What is its purpose...its function?
What is it for?

And, this one ain't about Glocks.
You are assuming that the angle on the breech face is the critical dimension because it has no tolerance which I believe is incorrect for the reasons mentioned. First it is customary in many companies that ”dimensions without tolerance are reference“. I have personal experience with this and seen it many times on drawings from many different companies.
If you are doubtful how can a dimension without a tolerance be determined to be good or bad on an inspection report? Further no machine shop would accept work where parts had to be perfect in order to get paid as they know there is a natural distribution in all parts.
 
Correct.

Since per the blueprints, the face of the barrel hood isn't wedged tightly against the breechface, that isn't it. either.

Now, this is why I like to see you get involved with technical discussions, Chief! You have the mind for it. It's also why you'll be able to wrap your head around the answer that eluded me for so long...and it came to me by playing with two rectangular Lego pieces.

It's about feeding. Specifically...controlled feed. <----Clue!

Rather than spelling it out, I want to let you shrink yourself down to .001 inch tall and watch the feeding phase in slow motion. I'm betting that you'll nail it.

For everyone watching this one, please refrain from commenting. The Chief is on it, and I don't want the waters to get muddied.

Hmmm...Gimme some time on this one. While I'm functionally familiar with the 1911 design from owning and shooting my 1991A1 for 32 years, I don't have the actual drawings handy to look at in order to process this information into a 3D operation in my mind along with all these details. So I have to build that image differently, which takes me longer.
 
I'm about to reveal it in the wee hours. I posted Part 1 as a lead-in. It'll all come together in Part 2. The explanation is a little complicated, but Browning's reasoning behind it was very simple...and that's probably why it confounded me for so long. I was hearing hoofbeats and looking for a Zebra instead of a horse.
 
Last edited:
It's not 90. It's 89 and 8 minutes.

Looking at the left side of the slide...muzzle end pointed left...the angle is like this. \ If it were like this / the angle would be specified as 90 degrees, 52 minutes.

OK, if the angle is as you described here, and it's about feeding, then I suspect it has to do with the following:

It involves scraping the top round out of the magazine as it chambers the round. When the back of the round clears the magazine lip, it has to slide up the breechface in a controlled fashion such that it is captured by the ejector while remaining in full contact with the breechface.

All this has to happen in the final fractions of an inch from the point where the round slips free of the magazine lip and the slide goes into full battery.

Some people may think that this is a minor detail, but it's not...probably because you have several moving parts at play here. You have the round moving up and into the chamber. You have the slide moving forward. You have some movement/motion of the barrel while this is happening. All the while you have some minor movements of these parts allowed by the machining tolerances. And let's not forget the person holding the gun, because his movements can affect things as well. If the breechface were 90 degrees you could potentially have problems with all this going on.

Metal actually bounces when struck. In many instances, it doesn't matter. For some, it does. Like for the metal contacts on pushbuttons, switches, and relay contacts for electrical and electronic devices. If you were to actually monitor the power flowing through such electrical contacts with an oscilloscope you'd see several spikes at the instant the contacts shut and the metal contacts actually bounced a few times before finally coming to rest in a closed state.

Anybody here have an older TI calculator and remember that sometimes when you pushed a button to enter a number, that number would pop up several times even though you only pushed the button once? That's switch bounce in action.

So, I think if the breechface was 90 degrees, then the impact of the slide on the round (and the round on the slide as it pops free of the magazine) as it's going through all the motions while chambering COULD cause a slight misalignment between the rim of the cartridge and the space between the breechface and the extractor pin. This could cause the gun to jam, or perhaps even break the extractor pin as well.
 
I'm looking forward to the wee-hours explanation! I'm working back 12s this week and I'm glad I got a moment to post my thinkings about this before you posted yours!
 
It involves scraping the top round out of the magazine as it chambers the round. When the back of the round clears the magazine lip, it has to slide up the breechface in a controlled fashion such that it is captured by the ejector while remaining in full contact with the breechface.
Bingo. I knew you'd figure it out.

All this has to happen in the final fractions of an inch from the point where the round slips free of the magazine lip
With the original, full tapered feed lips, the case rim is actually picked up by the extractor before it slips free. See the photo in Part 1.
 
Well, damn! I had to do a lot of thinking on this to get that.

My thoughts were that the whole process is powered by slide movement. Every mechanical action is fueled by this. So I asked myself "what mechanical processes are being driven by slide movement" and then broke those actions down into discrete movements of components. From there, it was questions like "where does this action start during the slide movement", "what happens when components connect", "what's going on as the parts in contact shuffle their positions", and "what do I know about material properties and basic mechanical operations".

It's my opinion that a lot of people actually know more than they think they do, they're just not used to connecting the dots from one tidbit of knowledge to another.

I must confess that I was also trying to figure out if this had anything to do with the ejection path of the expended cartridge. I came to the conclusion that it didn't really. It MIGHT change the trajectory slightly but there are other factors which probably affect trajectory more.
 
Dangit! I just read Part 1!

If I had read Part 1 before doing all that cogitating, I might have cued in on this sooner!

🤣 🤣 🤣
 
Dangit! I just read Part 1!
Interesting how a small, seemingly insignificant change in the magazine completely alters the feeding phase, no? Many people can't quite grasp the explanation until they see that photo...and then, you can almost hear the wheels turnin'.
 
Last edited:
Interesting how a small, seemingly insignificant change in the magazine completely alters the feeding phase, no? Many people can't quite grasp the explanation until they see that photo...and then, you can almost hear the wheels turnin'.

While grinding the gears, I did think about how the 1911 magazines for my Colt kinda flare open, but I hadn't realized they spread that far back.

I WANTED to pull out my 1991A1 last night and look it over but, but Uncle Sam kinda frowns on bringing firearms into the shipyard.
 
Last edited:
I would like to thank @John Travis for these posts. The knowledge shared may never be something I use; but it is there, and one never knows when some tidbit of information will come in handy.

I keep flirting with buying a 1911 just because; don't "need" one but I surely WANT one. Knowing how they work is a plus.

(There's this RIA double-stack a LGS has for under 5 bills that I've been coveting. . . . )
 
While grinding the gears, I did think about how the 1911 magazines for my Colt kinds flare open, but I hadn't realized they spread that far back.
Sounds like one of the "hybrid" lipped magazines.

Those came about as a result of the old AMU armorers' tool that swaged a timed release point into the tapered lips of the GI "hardball" magazines to use with SWC ammunition.

After WW2, Colt geared up for another government contract that didn't materialize, so they had thousands of magazines on hand. They used them with their commercial pistols until they were exhausted, and...having gotten rid of the machinery to make magazines...they had to use outsource vendors.

The engineers got busy in setting up a set of blueprints for the modified hardball magazines, and that's what was given to the vendors for their contract magazines. The design works as well with long OAL ball ammo as it does with shorter hollowpoint and SWC. A general purpose magazine of sorts. Of the three main vendors...Metalform, Checkmate, and OKAY Industries. only Check Mate offers them to buyers other than Colt.

And, when the Officer's Model appeared, with its 6 round stick, the feed lip design carried over...at least at first...and they functioned well, even in the chopped down guns. Now that everybody insists on adding a round, they've switched to the Shooting Star with its parallel lips with the attendant problems that come with it. I'm surprised that so many function as well as they do.

As an interesting side note...The 6-round OM magazines use the same follower and spring as the standard length 7-rounders...and the 7 round OM magazines use the same follower and spring as the standard length 8-round Shooting Stars.

Here are the three feed lip types. L-R Browning's "Hardball" magazine...Hybrid...Parallel lipped "SWC" type.

tn_lips_comparison_top.jpg
 
Last edited:
John - what's the purpose of the dimple and why is it located where it is?
 
John - what's the purpose of the dimple and why is it located where it is?
The dimple keeps the last round from jumping the magazine under recoil when the pistol jerks up and back and the cartridge tries to obey Newton and stand still. In the magazines with a timed release point, it's located just behind the release point. For full tapered "hardball" magazines, the location is at the same place on the follower, but farther behind the final release point.

Signs and symptoms are the slide locking back with the last round loose in the port and extractor losing tension quickly or breaking from snapover due to push feeding.
 
Last edited:
I've had those problems. I always wondered -given the stated purpose- why the dimple was not placed under the rim before the cartridge moves at all, rather than forward like it is.
 
why the dimple was not placed under the rim before the cartridge moves at all, rather than forward like it is.
Bill Wilson tried that and it didn't work all that well. If you watch a slow motion clip, you'll notice that on the last round or two, the ammuntion bounces up and down a couple times before it settles down against the feed lips.

About 95% of muzzle flip comes from the last half inch or so of spring compression. If the cartridge is in the bouncing process when the slide hits the frame, Newton 1 is in play and the round can still ride out of the magazine...and did pretty often with Wilson's attempt.

It can still happen even with Browning's dimple if the spring gets weak enough.
 
Back
Top Bottom