Fitting 1911 slide to frame question

[crashguy]

In a trade .. I got a complete used caspian upper for a 45 acp 1911…. It does not fit , the slide will not even engage the rails on the complete 1911 firearm frame (also in 45acp ) I presently have. Both are 5 inch . I do not want to alter the frame as it already has a properly fitted slide.
Question…
Is it acceptable to modify just the “new” slide to fit the “old” frame.

[AMG]

Cashguy: I have done several slides similar to your question. I would question whether the barrel in the new upper will work in the current frame. You might try to interchange the barrels to see if the link up will work. If you don't have a slide file, I would strongly recommend you buy it, the file has a safe edge to prevent removing too much material in the groves.

Arlin

[Gtek]

The old 1911 has been around for a long time and made and modified by many, and many manufacturers making it their way drifting from original dimensions. We are talking thousandths here and tolerance is a requirement. First thing I would suggest is before any "filing" is a complete dimensional check and documentation be done of your frame and both slides and see where you are at. Not being new where fitting is done, trying to move a machined slot up or down rarely ends with correct tolerances. Moving one line down does not fill the top one.

[Der Gebirgsjager]

Your thinking is sound in choosing to modify the slide rather than the frame. I doubt if anyone here can really tell you how to do that without actually viewing the parts.

DG

[M-Tecs]

It can be easily done by someone with the proper tooling and knowledge. Without either the tooling or knowledge not so much.

The video below is opposite of what you would need to do since the frame is off limits but starting at about 30 seconds it shows the measurement you will need to address.


https://www.youtube.com/watch?v=ni7hIiQsGLU

Once the slide is fit you may need to fit the barrel lugs.

[M-Tecs]

I use a milling machine but this is alternate method to fit the barrel lugs.


https://www.youtube.com/watch?v=AMcdDgd7W0U

[DougGuy]

Is it acceptable to modify just the “new” slide to fit the “old” frame. It's possible but that's the hard way of doing it. Since you can't get the frame rails to start in the slide, you would have to mic the thickness AND the width of the rails, then mic the slide and see where you need to mill so it will go on the frame. You would have to mill the slots in the slide to make them wider. It really is the bass ackwards way of fitting the slide and frame. You would need to mill the bare minimum for a tight forceful fit, then lap it out the rest of the way.

I got two complete AO lowers off GB, they were pulls from working guns, I had to lap the slides to the frames on both but they turned out a superior slide to frame fit. In this case, the slide would go partially onto the frame and I lapped it with just oil at first, which got them to go quite a bit farther, then started with the fine lapping compound, then finished up with just oil.

[crashguy]

Thanks to all….. I have some measuring to do and need some special files… but I’m now encouraged that it’s do-able.

[1006]

I have a dual caliber 1911 40/9mm that I had put together by my favorite gunsmith.

I ran into the same issue before deciding to surrender it to the gunsmith.

Mr. Cogen of Accurate Plating and Weaponry in Alabama finished it, and did a great job. The slide’s rail slots had to be deepened. When he was finished, he hard chromed the slide.

[jmorris]

I have made exactly one firearm that is a two slide, one frame pistol. Fitting the first one is pretty easy, fitting the second without altering the fit to the first set, was difficult enough I just put together two pistols now or get an SVI slide so you can swap the breechface in the same slide for other calibers.