how to check 1911 for lug engagement?

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InTheBlack

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When contemplating a used 1911 at a gun show, or even for peace of mind with a gun you have had for some time--

What can you look for in order to judge if the locking lug engagement between the slide and barrel is OK? Conversely, what sort of wear indicates bad fit?

Pictures would be helpful.

And if it looks bad, how much should the price be reduced for the cost of having a gunsmith fit it properly? -- assuming its not too far gone to be fixed.
 
I highly recommend Jerry Kuhnhassen's book "The Colt 45 Automatic, A Shop Manual". The first volume shows how to examine a 1911 and check everything including lug engagement and what happens when it isn't right. Lots of pictures.
 
re: Lugs

Howdy,

I second stans' advice on the manuals.

One problem comes that comes to mind is that, in order to determine
exact depth of lug engagement, you'll need modeling clay and some graphite...assuming that the seller will allow you to run a test on the gun.

There are a few things to look for if he will let you do a quick field-strip.
The inspection won't tell you anything about the exact mechanical engagement of the barrel lugs, but it will let you determmine if there are any problems.

Look at the front corners of the barrel lugs. They should be sharp and square to the bore axis. Any rounding off...radiusing on the corners... is
indication of a timing problem. If the pistol has had a barrel hand-fitted by a smith, there MAY be a light, 45 degree bevel on the corners, but that
bevel will be clean and well-defined.

Flanging is another sign of impending trouble. From back to front, scrape
the lugs with a thumbnail. If you feel a burr or sharp edge, there's a problem. If it's slight, and without any damage to the front of the lug as noted above, it's possibly an easy fix...No guarantee...but possibly.
Even if the light flanging is due to a more extensive problem, catcing it
before damage was done to the barrel and slide lugs makes it a viable
project if the price is right. The fix can range from a simple link change
or modification to machining the frame, to a barrel replacement.

Check the lugs inside the slide. If lug engagement is shallow, you'll notice
a "stepped" shape on the rear of the lugs...but that's only evident if the
gun has been fired enough to create the step(s) The barrel lugs may also
show the steps on the front of the lugs...but it's usually in the slide that you'll see it first.

If there's a timing problem, the flanging on the rear corners of the lugs in the slide will be evident, just like on the barrel. Scrape the lugs from front to rear with a fingernail to feel for the edge.

While light flanging can be dressed and smoothed...and the cause corrected if caught in time, radiused and/or reshaped barrel and slide lugs
will either put the gun into the "Wall Hanger" status...or the slide and barrel should be replaced if you intend to shoot the gun. It will likely function with this damage...but it won't function for very long...maybe 2 or 3 thousand rounds...and the accuracy will degrade pretty quickly due to the increasing fore and aft play in the barrel. Once the damage starts, it progresses quickly.

Hope this helps.

Luck!

Tuner
 
The touchy-feely advice is just what I was looking for; something you can check just by removing the slide without tools. The Kuhnhausen book is heavy reading and kind of presumes a lot of knowledge.

Now if someone would create a comprehensive index for his books, that would help a lot.
 
Seems to me.. couldn't you paint a little something on the lugs (the blue dye they use to check rear end gear engagement for truck axles comes to mind) and see how deep the lug engagement is by firing a few rounds?
 
mfree asked:

Seems to me.. couldn't you paint a little something on the lugs (the blue dye they use to check rear end gear engagement for truck axles comes to mind) and see how deep the lug engagement is by firing a few rounds

Howdy mfree,

Dykem or Prussian blue on the front of the locking lugs will give a
ballpark estimate...as in:

"Hmmm...Looks like about 75 or 80% of full depth."

...but it won't provide an exact measurement of lug engagement.
The only way to know is to know...ya know?

Cheers!

Tuner
 
Easy-Check

Dave said:

with a dial caliper. It should come up to about .50 + or- 2,3,4.
_____________________

ROFL :D Behave yorese'f!

Grab another cuppa joe and come on back, Cap'n! Not lug depth...
Engagement...Total overlap with slide lugs in-battery. Modelin'
clay...graphite...depth mike...

Welcome back, Dave. Wheredahell ya been for so long? Health is good, I trust...

Tuner
 
I been on my Drive-a-bout, Tuner. I was out in the old Desert Rat for 25 days having fun with family and friends. One and the same, Tuner. The lugs in the barrel engage the grooves in the slide when the barrel is locked up. Factory guns have roughly the same engqagement with about .025 to .030 of empty space between the barrel and the slide. The up and down is not as important as the fore and aft play in a standard barrel. When you have some slop all four ways, you cannot expect much accuracy or reliability in repeating the lock up. This is why we fit National Match barrels and Bushings so we don't have any play in any direction. We fit these barrels in such a way that there is no play in any direction, but without the recoil system installed, they will pass the gravity test by locking and unlocking as you tip the gun up and down. Hey, if I can do it, anyone can! I cannot see any way to tell what a 1911 barrel engagement at the counter in a gunstore, but a quick check would be to press down on the barrel hood and see what kind of play you have. If it springs at all, do not expect much accuracy out of it. That springing means that the lower lugs are riding on air and the barrel llink. Good luck!
 
Johnny, why not with a dial caliper, used in the correct manner? Measure the depth from the top of the slide to the hood, back it out of lock-up and measure it again, do a little math, etc....
It could go on all day measuring one of these things, but the test Dave described is probably as good as it's going to get at the sellers table or counter, and tells 90% of the tale anyway.

Thanks for the PM Johnny, I appreciate it. Haven't been myself lately, haven't even spoken to my very close friends in a week or so, just haven't been myself and cannot convince myself I need to be.
 
Measure it

Bill said:

Measure the depth from the top of the slide to the hood, back it out of lock-up and measure it again, do a little math, etc..

Yep..That'll work for a quick check. If I'm checkin' for engagement in a high-pressure/heavy use set-up, I like to use modeling clay to get a better idea of where #s 2 and 3 are. Stitch in time and all that. Also like to check for
horizontal in case #3 is takin' the brunt.

Things are gonna get better, Bill...It'll take an effort sometimes and sometimes not so much, but you'll be back in the thick of things soon.
Do what I did...Go buy junkers and put'em in shape to shoot. I did
one a month for nearly a year.

Take care,

Johnny
 
Too much work already on the bench and on the way for that, plus we are planning on starting up another class. That'll snap me out of it enough though.
 
My digital calipers have 2 ends. The rear end is a functional depth micrometer which gives virtualy the same numbers as my depth micrometer. If I had been a little smarter back when I bought the later I would have saved my money.

Dean
[email protected]
 
Thanks for the Dawg Story , Tuner. Fellina ate something bad on the trip and we are in the middle of "The Nights of a Thousand Poops" We are using lots of old towels and scrub brushes, inventing new words, and trying to concentrate on how much we love her. I am sure you know what I mean!
 
Night of a Thousand Poops

ROFL! Yeah...I know.

Feed her some cheddar cheese...a one-inch thick block of
Cracker Barrel Sharp two times a day will help...one with her supper and one 12 hours later. A half-teaspoon of Immodium AD will put the brakes on that problem in a couple of hours, and the cheese will help to firm things up until she's well. Call your vet for an okay on the Immodium beforehand. It works on the Collies like it was made for'em, but some breeds may not be tolerant. Never heard of any problems, but better safe than sorry.

Collies get the squirts a lot...Even a sudden change of diet will trigger
it...so I've been there and done that a few times, havin' 4 of'em and all...:rolleyes:

Woof!

Tuner
 
Be DAMNED if a .45 Luger wouldn't end the 1911 forever!
Click to expand...

They've already tried that.

Serial #1 was probably destroyed after the test was completed, and Serial #2 is the only known example in existence.

Then the U.S. Army went on to choose the 1911.

Of course. :D
 
Here is how I check lug engagement:

Unloaded and fully assembled, place a piece of popsicle stick between the
end of the barrel hood and the breechface. Slide is as forward as it can go,
barrel is pushed up and forward but out of battery. Use depth rod of
calipers to measure from top of slide to top of barrel at front of ejection
port.
Remove popsicle stick, allow slide to go fully forward, barrel in battery,
measure once again from top of slide to top of barrel at front of
ejection port.
Subtract the latter from the former........voila! Lug engagement.:)
 
Hah! I'm not crazy, I knew it. That is the way I was tring to 'splain it, minus the popscicle stick. I se where that would give a more consistant reading as your not fighting to hold it in one place. I'll let the popscicle stick I use for slide/frame fitting do double duty, wait, I'll just eat another popscicle instead, yeah, that's what I'll do.
 
Sticks!

Yeppers...That'll tell what ya need to know on the first lug...but
what's behind lug # 2 and lug #3? :p

I use modeling clay and mica or graphite...D'ruther use Plasti-Gage (tm) when I can get it, but it's kinda scarce, since auto machine shops don't use it that much any more. Plastigage for the barrel slots for slide lug engagement...Modeling clay in the slide lug slots for barrel lug engagement, since the lugs are usually shorter than the depth of the slide slots....and generally the front lug is a bit shorter than the center lug to let the slide get by it when it links down.

You may have to order Plasti-gage from your friendly, neighborhood
auto parts jobber. Most of'em don't keep it in stock nowadays...

Luck!

Tuner
 
Another Great Popsicle Stick Trick! I am curious to know what the Tuner does with the information gleaned from knowing the engagement of the front upper lugs in the slide at lock up. What adjustments can you make, if any? I have ignored these enagagements forever and I feel I may be missing something here. Thanks in advance for your help.
 
I am an amatuer metal worker (retired interventual cardiologist) so I use tongue depressors rather than of popsicle sticks as I have an easy supply. I also have some brass shims. I do not have the best eyes and have a tremor so things that hold themselves in position are necessary for me even when I measure and recheck things - I just stumbled on to elite pistolsmith Chuck Rodgers technique.

Dean
[email protected]
 
Re: Knowin' is Knowin'

Dave asked:

I am curious to know what the Tuner does with the information gleaned from knowing the...

Howdy Cap'n.

It started back when I was playin' around with "Buffalo Stomper"
loads for our old Slabsides. I had a buncha pistols to play with, since
I was in the habit of takin' in basket cases and makin' shooters out of'em.

250-280 grain hard cast bullets started after a guy gave me a couple of molds that he used for his .45 Colt revolvers...and had gotten too old to fool with. Nice, RN FP bullets that fed like grease thru a goose in most of
my pistols...and I started bumpin' up the power charges so I could knock
ballistic pendulums silly. I also got to noticin' a problem with some guns.

The lugs were gettin' beat all to hell-and-gone in some pistols...slide and
barrel lugs...but others didn't seem to know the difference. Soooo...
I started checkin' things, and I saw that as long as the forward barrel lug...#3...was sittin higher in the slide's slot than about .040 inch...and the middle lug...#2...was about .050 deep...with full engagement on #1, the guns would stand up to the heavy bullets at 800-850 fps waaaaay longer than when the engagements were in the "average" range, with a lot of
air above the barrel lugs....even with good slide lug contact in the barrel slots. Not too critical with standard .45 ACP pressures and 230-grain bullets...but a lot moreso when the pressures and recoil forces go up.
I figure that some of those loadings were pretty...adventurous.:rolleyes:
I sheared a few barrel lugs in those days...but GI barrels and slides were cheap at the shows, so I pressed onward.

Then...when I started welding barrel lugs up and fitting them so as to get a
full mesh engagement...slide lugs in full engagement with the barrel slots,
and barrel lugs in the slide slots as close to 100% as I could get'em and still let the barrels link down far enough to let the slide pass over'em...the
guns would stand up to about triple the number of those rounds.

I even lowered the saddles a little to let the barrels link down farther so
I could set the barrel lugs deeper into the slide, but ran into a point that
linkdown timing was more the limiting factor than lack of clearance. Of
course, the forward lug was the fly in the ointment due to the fact that it's
sitting higher than the other two when the barrel is in linkdown. No
matter how much clearance I got at the back...the barrel would fall only
so fast. I could get very close to full mesh on the middle lug...but not the forward one.
_____________________________

Dean...Your dial caliper indeed has a pretty good depth mike on the bottom,
and as long as you're dealing with tolerances that are typical in the 1911
and other pistols, you're golden. Most dial and vernier calipers are accurate
only to within plus/minus .001 inch..but if you need to split that into tenths
of a thousandth, you need a depth mike with a vernier scale for a more exact measurement. The wider, more stable base on the mike also makes it easier to consistently center on a radius than the bottom of a caliper. Unless you're well-practiced, you can take 3 such depth measurements and come up with 3 different results with a caliper. Not a critical point
on a 1911 pistol, but as you begin to work with closer tolerances, you'll
see the difference quickly. If you're truly bitten by the bug, it's natural to
get the equipment and dabble with making your own tooling, jigs and fixtures. It's a never-ending quest that borders on mental illness. Welcome to the world of a toolmaker...my world.:D

Cheers all!

Tuner
 
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