Sudden Impact
Howdy romulus,
The barrel is stopped by the back of the lower lug hitting the frame.
The little U-shaped cut at the bottom is for the link. If that surface is
too far forward, or the lug is positioned too far to the rear, the barrel can getinto a slight bind between the frame and slide before the barrel is fully down and out of the way. The lugs get rolled by the slide as it passes over.
To check, remove the recoil system from the gun, and leave the bushing in.
Push the slide briskly to battery and draw it back .250..or a quarter-inch.
When the rear edge of the trianglular safety cut in the slide is flush with the back of the frame...it's pretty close. AT THAT POINT...the barrel should be fully linked down, and there should be a small gap between the top of the barrel and the underside of the slide. I like to see .018-.020 inch, though .012-.015 will do, if the linkdown begins early enough.
Don't push on the barrel hood to get the clearance. It should fall by itself.
If you have to push on it, the link may be a little long from center-to-center
and is in a slight bind between the lower lug and slidestop pin. I've seen a
slightly overlength link cause the lugs to roll the way that you describe,
though not very much. Most often, the long link will cause a slight ridge
on the tops of the locking lugs, or only on the front one...with the front
corners just lightly radiused.
Barrel and slide move together for a short distance before the barrel begins to fall. On ordnance-spec guns, this is usually between .090
and .110 inch...with most falling somewehere between those two points.
You'll have to move the slide very slowly to catch the exact point that the
barrel starts to drop, and you may have to repeat it several times to see
the point exactly. Linkdown starting a little too early is better than a little
too late. I've seen it start as early as .060 inch of slide travel without ill
effect. Match-grade pistols tuned for accuracy can go as far a .125 inch, but that seems to be about the max, and that's if all else in the cycle is
precise. To find the point exactly, you'll need a dial indicator zeroed on the
back of the slide with the pistol mounted in a vise.
Timing issues like what you describe is often the result of dropping a non-specific barrel into a frame. This happened a lot on GI pistols during arsenal rebuilds. If yours is an old warhorse, this is probably what happened.
Other things that can cause it are:
Loose link pin holes that allow the link to move back and forth until the hole is eg-shaped. Linkdown timing is delayed.
Somebody installs a link that is way too long, thinking he's getting a tighter lockup and better accuracy. This also delays linkdown timing, and with the link bearing the load of vertical lockup, eventually leads to the wallowing of the pin hole.
Somebody has noticed that the slidestop pin is binding in the link with the
barrel held down and back in the frame, and elongates the bottom of the large hole in the link to let the slidestop engage the slide for a more reliable slidelock on empty. When the lower part of the hole is elongated, the effect is the same as a long link, and linkdown timing is delayed. The correct area to relieve the link hole is at the top, near the lug.
Hope this answers your questions. Also hope that slide is okay.
Luck with your project!
EDITED FOR BRAINFART: re: Lower lug FEET...hitting back of frame.
Rear of the lower LUG hitting the frame is correct. Sorry. Haste and
typos will be my downfall. There are conflicting views about whether the barrel should be supported at the back by the frame bed, or held slighly off the bed by the feet contacting the radius in the frame. This supoort shouldn't hold the barrel off the bed by more than about .001 inch. Most
barrels do fall the the bed, and either way seems to be okay.
Tuner
