Slide to Frame Fit
Tightening the clearances between the slide and frame are done with different techniques, depending on the individual situation encountered with each gun. Pistols that come as complete functioning firearms generally have a slide and frame that readily fit together with clearance left over. Slides and frames purchased as parts often are machined to dimensions that result in the frame and slide being unable to fit together due to interference. Depending on which circumstance exists, different techniques are required to make the slide and frame fit together with the smallest feasible clearance.

Interference Removal Fits
In the simplest terms, all that is needed to fit up this situation is to remove controlled amounts of material that is preventing the two parts from fitting up. This requires taking accurate measurements and making a plan to remove the interfering material in an accurate manner. Removal is usually done with a precision surface grinder and/or an accurate milling machine. After the parts are machined to a point that they will just fit together with force, they are lapped with ultra fine compound to a free-running fit, then cleaned and oiled.

Clearance Removal Fits
To close up existing clearances to make a tight fit, several methods are available to remove the existing clearance. The method (or combination of methods) used is dictated depending on where the clearance exists and how much clearance exists. The methods used consist of peening the frame rails down to remove vertical clearance, squeezing the bottom of the slide to remove horizontal clearance as well as welding and remachining the frame rails to accomplish both. Also, Accu-Rails can be installed to remove both vertical and horizontal clearance. The decision of which is the most appropriate is made after accurate measurements are taken to determine where the clearance exists and how much needs to be removed.

After a lot of experience with slide tightening, I have arrived at the conclusion that welding and remachining has more advantages and fewer risks than the old “squeeze and peen” method. I have never cracked or broken someone’s slide, but I know one day it will happen. I’m sure it will happen to something that is not readily replaceable. One the positive side, I believe you get superior bearing contact with the weld & remachine method between the slide and frame. This should equate to an extended service life, compared to other methods.

This operation is done exactly like it sounds, a controlled weld bead is applied with a TIG welder adding material to the frame rails. This is done at the front and rear sections of frame rail on each side. After welding, the rails are re-machined, hand-fitted and lapped to result in a zero play, free running fit.

Acc-u-Rails are a unique way of solving the slide-to-frame fitting dilemma. They are hardened round steel rods that are installed into grooves that are machined into both the slide and frame. The rods have a very short end section that is bent to 90 degrees and inserted into holes drilled into the frame. This bend retains the new rod in position, yet allows it to be replaced in the future to take up for any minor wear. Acc-u-Rails really shine in two respects: If you have a lot of clearance to get remove and don’t want to weld the frame, Acc-u-Rails are your best alternative. The other situation would be if you have a stainless or aluminum frame, installing Acc-u-Rails will give you a tightly fitted, steel-on-steel bearing surface with the slide. This would fix the issue of wear on an alloy frame or galling on a stainless frame. Acc-U-Rails are the only feasible way to tighten the slide to frame fit on an alloy framed pistol.