Building a 1911: Fitting the Slide and Frame

There are any number of reasons that fitting the slide to the frame should be the first operation when building a 1911:

  • A fitted slide and frame is a prerequisite for several other steps, such as staking the plunger tube, fitting the barrel, and installing the firing pin stop.
  • The parts which could be installed prior to slide fitting would just have to be removed later when performing the fitting.
  • If, to pick a random example, one is waiting on parts, then doing the slide and frame is one of the few options available.
  • Lapping a slide into place is a pain in the butt and is therefore best gotten out of the way as early as possible.
  • Once the slide is in place, you can see what the gun will look like and and get excited about how cool this is gonna be.

Naturally, it was only the more mature of those options which led me to begin the laborious process of convincing an undersized slide to make its way onto an oversized frame. And undersized/oversized theywere: Although the height of the slide and frame rails matched up verynicely, permitting the slide to start onto the rails, the width needed addressing. The frame was 2.5 thousandths wider at the rails than the corresponding gap inside the slide.

The options at hand were widening the slide rails or narrowing the frame. I discarded the slide rails out of hand due to the difficulty of that cut, even with machinery. For a while I was tempted to use amilling machine to cut down the rails, but hesitated due to mypreviously established tendency to remove metal a little too fast. Finally, upon advice, I settled on a sheet of glass, a piece, of sandpaper.

Thanks to the 1911’s flat frame cross-section, it’s possible to narrow the rails by placing a sheet of sandpaper on a piece of glass andsliding the entire frame across this flat surface. A couple swipes oneach side before flipping permits narrowing the entire frame, including the rails. All it takes is a little time.

sanded frame

Of course, dimensionally identical parts is a class of interference fit; however, a 1911 slide needs to, well, slide. An amusing irony of getting two tight parts to slide past each other is that instead of using a lubricant, the best approach is to apply an abrasive. That’s what I did.

lapping paste on frame

That’s non-embedding garnet lapping compound. For years I’ve applied this stuff with a toothpick, awkwardly smearing globs of the thick paste onto surfaces and then snarling as it fell off, but this time it finally occurred to me to simply use a finger to scrape some compound out of the container and wipe it onto the slide. It worked like a charm, but made me spend a few minutes seriously considering whether I was smart enough to be building a gun. Fortunately, the sunk cost fallacy came to the rescue: With all the time and money invested thus far, it would be foolish to stop now! Thus mollified, I picked up the slide and went to work.

The process I used for fitting the slide consisted of shoving the slide onto the frame until it stuck in place, then using a rubber hammer to whack the front of the slide, shoving it a bit farther back than manual strength alone permitted. Then the same hammer would be used on the rear of the slide to free it from the frame until it could
be shoved back again by hand. Repeat.

lapping paste with slide

The only variety in the process comes when the lapping compound has shaved off enough metal that it starts to lose efficacy. You can see the signs of this in the picture above: Tan compound turns black with super-fine iron shavings and it gets easier to shove the slide back. That’s the sign it’s time to remove the slide, clean all the compound off both frame and slide, reapply, and start again. That’s right–when things get easy, you have to stop and make it difficult again.

One interesting side effect of the lapping process was that the rear of the slide ended up getting slightly polished due to trace amounts of lapping compound getting picked up by the rubber head of the hammer and pounded against the metal. Abrasive polishing: You saw it here first.

Finally the desired final results were achieved:

slide back

The slide still has a bit of stickiness at its most rearward travel, but given that the recoil spring guide rod’s flange will prevent it from going all the way back, I decided to let it slide. (Get it? Get it???) At long last, the laborious and finicky process of slide fitting was complete and I could now move on to the laborious and finicky process of fitting the barrel…after first performing the laborious and finicky process of cleaning lapping compound out of every single crevice in both slide and frame.

Addendum: Forgot to mention the make of the slide and frame. The frame is a Foster Industries frame. These frames are basically rebranded Caspian Arms products. The slide is one of the Palmetto State Armory 1911 slides which PSA liquidated due to cosmetic changes.


Chris has absolutely no qualifications to justify speaking with authority on any gun subject whatsoever. He compensates for being a poor shot by embarking on quixotic gunsmithing projects of both mediocre quality and dubious value. Because his taste in firearms runs to overpowered and outdated designs, Chris' opinions on guns should be treated with suspicion.

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