Barrel to slide lug contact observation

[egumpher]

Hello,

I build a home built custom last year and was fortunate enough to achieve three lug contact between the barrel and slide (mostly luck ). This was using a Kart Easy fit barrel.

Yesterday I just shot my 1800 round after chrome which is about 2200 after I install the barrel. While cleaning and inspecting the parts yesterday I noticed that the number one lug contact area isn't shaped like the contact areas of lugs two and three.

Here is a picture of the slide lugs:


Here is the lug to barrel contact areas: (yellow is shown bellow the contact areas)


Here are some pictures that show that the number one lug contact is mostly to the left

Barrel in battery with full lug contact (91% of available vertical engagement)


Here is a link-down photo showing contact on the left side of the slide lug.


I find it interesting that most of the number one lug contact area in to the left of center of the slide.

I wonder if this is by design?

Rgds
Eric

[niemi24s]

Hello Eric:

I wonder if this is by design?

There is nothing in the Ordnance blueprints that indicates it's by design. Whatever contact there may be would be even from side to side, and not concentrated on one side. Maybe just something a tad off in the manufacture of the barrel and/or slide?

Or possibly more chrome got deposited in some areas than got deposited in other areas (if that's even possible)?

Cheers

[BigJon]

The lug contact marks you're seeing are from cycling not from in battery. Most often mention of lug contact is in regards to the lug recess faces.

Best,
Jon

[egumpher]

Thank you Jon,

So the marks are from link down when the lugs are pulled down out of battery?

The recoil spring should hold the barrel back at link-up...correct?

When I set-up the barrel I dychem blued the barrel lugs. Installed the barrel in the slide with the bushing. Then I whacked the back of the barrel knees with a rubber mallet to see how much lug contact there was when the barrel was horizontally forward (locked) in the slide.

I removed some material from the barrel lug faces until I got all three lugs to contact. The only drawback is that I ended up with 6-7 thou barrel movement / hood gap and a weird number one lug contact profile. I thought that it was a small price to pay to guarantee three lug contact.

Rgds
Eric

[BigJon]

Removing material from the barrel forward lug faces is fine, but should be done before hood fitting. The recoil spring only controls the slide. With the barrel tilted up at the chamber end 52' in battery the tops of the lugs can't touch, only when cycling. the marks on the are from the top of the barrel chamber area. Few 1911's have all three lug faces in contact with the slide, many only one. I do agree more is better, mostly for accuracy, more contact.

Best,
Jon

[egumpher]

Hello,

More:
Now that the barrel lugs are equalizing after 2000+ round I thought that the contact area would become more uniform.

Rgsd
Eric

[egumpher]

Removing material from the barrel forward lug faces is fine, but should be done before hood fitting. The recoil spring only controls the slide. With the barrel tilted up at the chamber end 52' in battery the tops of the lugs can't touch, only when cycling. the marks on the are from the top of the barrel chamber area. Few 1911's have all three lug faces in contact with the slide, many only one. I do agree more is better, mostly for accuracy, more contact.

Best,
Jon

Thanks again,

I tried and tried and tried to measure the barrel and slide to fit the lugs before I cut the hood but it didn't workout that way......there is nothing like experience huh...

I wanted three lug contact for durability. All of my other production 45s experience some type of wear/breakage around 3000 rounds for what ever the reason so I started a project determined to build a more durable 45. My Springfield and Colt both went back for warranty work around 3000 rounds.

Rgds
Eric

[niemi24s]

Hmm-m-m. Barrel goes max forward in slide when gun is fired. This means the forward vertical surfaces of barrel lugs/recesses come into hard pressure-locked contact with the aft vertical surfaces of the slide lugs/recesses. Like in this:



And that's where I see the indications of contact on the slide lugs in Eric's photos. What am I missing here?

[egumpher]

Hmm-m-m. Barrel goes max forward in slide when gun is fired. This means the forward vertical surfaces of barrel lugs/recesses come into hard pressure-locked contact with the aft vertical surfaces of the slide lugs/recesses. Like in this:



And that's where I see the indications of contact on the slide lugs in Eric's photos. What am I missing here?

Exactly why I wanted three lug contact..........but the slide and barrel are harder than the original 1911s.

I do want to understand if the marks I see are from "pressure-lock" or cycling..... inquiring minds want to know.....


Edit added:

Recall that the original 1911 design was build with soft slides and proof pressure ammo was fired by the armorer to equalized the all three lug contact.

Modern modified Browning designs use one large lug because of the advance in materials (hardened slides) now allow/accept one lug.

Thanks again
Eric

[1911Tuner]

I do want to understand if the marks I see are from "pressure-lock" or cycling.....

An analysis...going on what I can see in the first picture...and that's not really the best way to diagnose it, but...

It looks like the lugs are being deformed from insufficient vertical engagement, and that the barrel fit started out with only lug #2 bearing the brunt. As #2 defromed, it brought #3 into the game, and as 2 and 3 deformed, it eventually got around to lug #1. Slide lug #1 wasn't/isn't dead square to barrel lug #1, hence the uneven wear pattern. Or...Barrel lug #1 isn't dead square to slide lug#1. It's 6 of one/half dozen of the other.

Check the barrel lugs for similar stair-stepping and attendant flanging at the top front corners, and re-check the headspace while you're at it. My guess is that it's grown a bit, though not likely enough to cause a problem.

Now that Lug#1 is coming in, the deformation probably won't progress very rapidly...but be sure to eyeball barrel lugs 2 and 3 for indication of cracking or shearing about every 500 rounds for a while.