1911Tuner
Moderator Emeritus
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I know ya have, Dean...and it looks like Kart and Caspian have gotten together on their specs. Kudos to'em...but if things ain't exactly in the groove, there can be problems.
AFAI can tell, Kart assumes that the slide will be fairly perfectly in-spec...and that the vertical dimensions from slidestop pin centerline to the inside tops of the slide's lug slots are likewise. If so, the Easy-fit is good to go as per instructions. It also seems to be designed to fit horizontally to the first lug...the strongest one. Not the stoutest lockup in the world, but it'll do for standard pressure.45 ACP ammo.
But let's assume for a minute that the slide isn't truly in-spec in all aspects.
Say...The #2 lug is a little too far rearward...about .003 inch out of spec.
Let's also assume that a given barrel has #2 lug located just a wee bit too far forward. In-spec, but right on the peg.
When the overlength hood is cut to allow the barrel to just enter the slide, it doesn't bear against the #1 lug. It's fitted to #2...a weaker, less supported lug. Let's also assume that lug 1 is also kissin' air, and therefore offer no
help in bearing the brunt of the pressure when the round fires. Guess what will happen to Lug #2...That's right. It will deform rearward...set back. As the setback occurs, the slide will move farther and farther from the barrel when the gun is fired. Headspace begins to grow. If we're lucky, the air space in front of lug(s) 1 and 3 is very slight...maybe .002 inch or so. As #2
sets back enough to let one of the others take a share of the shock load, things get stronger. Headspace is still good, if it was close to minimum to start with. If the gap is larger...say .005 or .006 inch, the lug will continue to deform and set back...and will likely crack or shear. NOT good.
Now, let's move to vertical lug engagement and assume that instead of full engagement, the vertical stackups only allow about .030 inch of engagement and overlap when the E-Z Fit pads allow the gun to go into battery. (Same gun) Tight vertical lock...but only a little more than half the available surface area to contain all that pressure. Imagine two hammer heads being slammed together dead on-center. Then imagine them being slammed together off-center by 50%. In this gun, the load-bearing lug will deform twice as fast as another gun with one lug bearing, but with full depth...and about three times as fast as another gun with the strongest lug bearing...#1.
Let's also assume...just for the sake of debate...that our boy has decided to try jumping into .45 Super ballistics. After all...He's got a bank-vault lockup...Right? Guess what'll happen after about 500 rounds of that stuff. Even if the lug doesn't crack or shear...which it likely will if the airspace between the two that don't help is larger than about .003 inch...The headspace will increase at an accelerated rate, and what started out as near-minimum will quickly reach maximum. Another hundred rounds, and he'll start noticing slightly bulged cases ahead of the web...and shortly afterward, he'll probably blow one out...at .45 Super pressures. A .45 ACP blowout is bad. .45 Super would probably be catastrophic. Scary stuff.
Now then...If you don't gauge the slide to determine exactly where the lugs are...How are ya gonna know what kind of fit you're gettin' with your new match-grade barrel? If you do gauge it, you can determine how to fit for
equal lug engagement, and reap the benefits of the strongest lockup that the Colt-Browning design will provide...assuming that you also have full vertical engagement...which you might get with the E-Z Fit, and you might not...unless all is well within-spec...which many slides aren't. Caspian notwithstanding, I'd guess that you'll not likely find one in ten that will allow full depth AND equal horizontal engagement on even two lugs with a given barrel without some adjustment.
At any rate...Even with only .030 inch in the vertical...if you have all three taking an equal share of the force, you still have a total engagement area equal to two lugs with .045 inch each...or 90% of full depth with one lug...and one of those is the most supported lug...#1...which is probably
equal to 90% of the strength of the other two combined.
Clear as mud?
I know ya have, Dean...and it looks like Kart and Caspian have gotten together on their specs. Kudos to'em...but if things ain't exactly in the groove, there can be problems.
AFAI can tell, Kart assumes that the slide will be fairly perfectly in-spec...and that the vertical dimensions from slidestop pin centerline to the inside tops of the slide's lug slots are likewise. If so, the Easy-fit is good to go as per instructions. It also seems to be designed to fit horizontally to the first lug...the strongest one. Not the stoutest lockup in the world, but it'll do for standard pressure.45 ACP ammo.
But let's assume for a minute that the slide isn't truly in-spec in all aspects.
Say...The #2 lug is a little too far rearward...about .003 inch out of spec.
Let's also assume that a given barrel has #2 lug located just a wee bit too far forward. In-spec, but right on the peg.
When the overlength hood is cut to allow the barrel to just enter the slide, it doesn't bear against the #1 lug. It's fitted to #2...a weaker, less supported lug. Let's also assume that lug 1 is also kissin' air, and therefore offer no
help in bearing the brunt of the pressure when the round fires. Guess what will happen to Lug #2...That's right. It will deform rearward...set back. As the setback occurs, the slide will move farther and farther from the barrel when the gun is fired. Headspace begins to grow. If we're lucky, the air space in front of lug(s) 1 and 3 is very slight...maybe .002 inch or so. As #2
sets back enough to let one of the others take a share of the shock load, things get stronger. Headspace is still good, if it was close to minimum to start with. If the gap is larger...say .005 or .006 inch, the lug will continue to deform and set back...and will likely crack or shear. NOT good.
Now, let's move to vertical lug engagement and assume that instead of full engagement, the vertical stackups only allow about .030 inch of engagement and overlap when the E-Z Fit pads allow the gun to go into battery. (Same gun) Tight vertical lock...but only a little more than half the available surface area to contain all that pressure. Imagine two hammer heads being slammed together dead on-center. Then imagine them being slammed together off-center by 50%. In this gun, the load-bearing lug will deform twice as fast as another gun with one lug bearing, but with full depth...and about three times as fast as another gun with the strongest lug bearing...#1.
Let's also assume...just for the sake of debate...that our boy has decided to try jumping into .45 Super ballistics. After all...He's got a bank-vault lockup...Right? Guess what'll happen after about 500 rounds of that stuff. Even if the lug doesn't crack or shear...which it likely will if the airspace between the two that don't help is larger than about .003 inch...The headspace will increase at an accelerated rate, and what started out as near-minimum will quickly reach maximum. Another hundred rounds, and he'll start noticing slightly bulged cases ahead of the web...and shortly afterward, he'll probably blow one out...at .45 Super pressures. A .45 ACP blowout is bad. .45 Super would probably be catastrophic. Scary stuff.
Now then...If you don't gauge the slide to determine exactly where the lugs are...How are ya gonna know what kind of fit you're gettin' with your new match-grade barrel? If you do gauge it, you can determine how to fit for
equal lug engagement, and reap the benefits of the strongest lockup that the Colt-Browning design will provide...assuming that you also have full vertical engagement...which you might get with the E-Z Fit, and you might not...unless all is well within-spec...which many slides aren't. Caspian notwithstanding, I'd guess that you'll not likely find one in ten that will allow full depth AND equal horizontal engagement on even two lugs with a given barrel without some adjustment.
At any rate...Even with only .030 inch in the vertical...if you have all three taking an equal share of the force, you still have a total engagement area equal to two lugs with .045 inch each...or 90% of full depth with one lug...and one of those is the most supported lug...#1...which is probably
equal to 90% of the strength of the other two combined.
Clear as mud?