Mis-Aligned slide stop hole cause locking lug damage?

[Ash]

Mis-Aligned slide stop hole cause locking lug damage - With Photos Now

I have a pistol, a steel-framed AT-84 with heavily-worn locking lugs on both the barrel and the slide. A 1mm headspace issue has arisen as a result of the lugs pounding against each other due to the deformation. It is in 9mm parabellum.

Now, I bought the pistol knowing the issues with the slide and barrel, intending to convert it to 40S&W with a Tanfoglio (small frame) slide and barrel. However, upon inspection, I noticed that the interior of the slide-stop hole has some flashing, as if it has been re-welded and then re-machined. It is not present on my other AT-84. I cannot say this has happened, but there are other features of the frame, like a missing import mark (Action Arms), plus a thorough re-finishing, that leads me to believe that at some point the frame deformed about the slide stop (or that the slide stop hole somehow was deformed), and it was welded-up and re-machined.

If the hole were slightly off, would this lead to the problems in the barrel and the slide? If so, then I won't waste my time on the conversion and assume I have an expensive case for the incidental parts I might need sometime in the future. What thoughts are there here?

Ash

 

[Ash]

Anyone?

 

[BBBBill]

Pics would help. Careful evaluation/measurement of the frame by someone with the tools/knowledge of the platform would be better. I don't know the platform well enough, but I will be watching for the answer.

 

[Ash]

Here are photos. The first photo shows the diagram of the interior of the pistol from a bit of a distance. The second shows the hole itself. Notice the flashing I mentioned. The entire frame has been refinished in hard chrome. But, the import marks are now missing (Action Arms imported these). The last photograph is of the locking lug deformation. This is the same on slide AND barrel.

 

[rbernie]

Have you taken a set of measurements to determine if the slidestop hole is consistently located, side-to-side?

 

[Ash]

No. But if the holes were off, could this lead to the questions at hand? Also, does this look re-machined?

 

[1911Tuner]

The deformation at the rear of the slide's lugs and corresonding front of the barrel's are caused by insufficient vertical engagement of he barrel into the slide. Another way...the barrel isn't being "lifted" high enough to place more surface area of the lugs into contact. I see this one a lot on early Norincos, old Thompson Auto Ordnance clones, and some Series 70 Colts, and have seen it on a few early Series 80 Colts.

When the gun fires, the bullet exerts a forward drag on the barrel under high pressure and frictional force. At the same time, the equal/opposite force on the slide drives it rearward...and the slide pulls the barrel backward with it...against the bullet's drag.

That places a high shearing force on the lugs in opposing directions. If there's only 25-50% or so of the lug's face involved...this damage is the result. If the barrel has a lot of horizontal slack in the slide...the damage occurs faster because the slide lugs get a longer running start at the barrel lugs before contacting...and is thus an impact.

If the slidestop pin hole is located too low and doesn't provide enough "lift" for the barrel...that can be where the problem is. If the barrel's lower lug/cam isn't to spec...that can also be what causes it. If the barrel or slide lugs themselves are too small...another potential trouble spot. If the slide itself is postioned too high on the frame...either due to out of spec frame OR slide rail location...another place to look.

And, yes. That sort of deformation increases headspace...and it increases it in the kaboom direction. Short answer. This one belongs to the manufacturer.

 

[Ash]

This was made in the mid 1980's by ITM in Switzerland. The numbers on the barrel and slide match each other. Shoddy manufacture is not what the Swiss are known for, but all things are possible. The large amount of refinishing, plus the flashing around the hole, made me wonder if it had been re-machined.

Ash

 

[1911Tuner]

Sounds like maybe a crack adjacent to the hole was welded and the hole re-drilled...in the wrong place.