In Parts 1 and 2 of this series, we fitted the hood and lugs of a Kart barrel to our pistol. Next, we will select a link. The sole function of the link is to unlock the barrel. It should never be used to increase lockup.
When the pistol is fired, the slide and barrel begin moving to the rear together for a very short distance until the link pulls the barrel down out of engagement with the slide as it continues to the rear. As the slide moves forward to chamber the next round, the bottom lugs ride the slide stop back up into position.
Links are selected based on the distance, center to center, between the two holes. Sizes are available from .268" (Wilson #1) to .288" (Wilson #5) or larger. A standard link measures .278" (Wilson #3). The slide has been tightened on our project gun, which involved beating the rails down, so we will need a link a bit shorter than the standard one.
Remember, the bottom lugs lock the barrel and the link unlocks it so we don't want any hard contact between the link and slide stop when the barrel is locked.
The inside top surface of the link should be slightly lower than the lug locking surfaces. A few thousandths is fine. When the slide stop is held against the lugs up and to the rear in normal firing position, you should be able to wiggle the link slightly fore and aft. That movement indicates it is not binding. In this case a Wilson #2 (.273") link fit nicely.
The link pin should fit the hole in the barrel snugly so it doesn't fall out when the pistol is disassembled. Link pins are available in sizes .154" and .156" and the link pin hole can be adjusted with a reamer if necessary. A .154" pin slid into our Kart barrel with a nice press fit.
Check link-down clearance with the slide stop. It should follow the contour of the barrel lugs closely as it moves from locked to unlocked position without binding on the corner of the lugs. If it hits the lugs, you can clearance the inside bottom of the slide stop hole slightly with a chain saw file and radius the corner of the lugs a bit where the lug cutter left a sharp angle.
Assemble the barrel, slide, bushing and slide stop on the stripped frame and manually function the pistol to check for any binding during unlocking/locking.
In Part 4 of this series we will fit the barrel bushing.
Links are available in a variety of sizes identified by a number stamped on them. The size indicates the gap between the holes. These are by Wilson Combat.
Select a link that is slightly shorter than the distance between the link pin and locking lugs. The link's function is to pull the barrel down on firing.
Move the slide stop through its normal range of motion to check for interference with the lugs. To should follow the barrel lug contour closely.
When holding the slide stop hard against the top rear of the lugs in lockup position, you should be able to wiggle the link slightly.