Fully Customized 97B

[IDescribe]

why does rail fit have least effect on accuracy?   

Because in the time it takes for the bullet to leave the barrel, the slide's movement is somewhere between almost nothing and nothing.

WHAT does have greatest impact on accuracy?

Barrel and barrel fit.

[schmeky]

The best thing I can tell you is to read Jerry Kuhnhausen's 1911 Manuals, Volumes 1 & 2.  Any decent smith has to read these cover to cover, and use these for building bullseye grade 1911's.

Just a snippet, but barrels don't lock up in frames, per se, they lock up in the slide. The barrels muzzle, upper barrel lugs, and breech lock up in the slide, not "in" the frame.  Also, sights are mounted on the slide, not on the frame.

This is all in the Kuhnhausen manuals.     

[handgun2]

ok,

please bear with my education.  But if you have an excessive amount of 'clearance' in slide and frame fit, won't the slide potentially 'end up' in a different position and thereby creating a accuracy issue from slide in different final location/prior to next shot than previous.

thank you for taking the time to explain.

respectfully,
kevin

[schmeky]

Kevin,

Good question easy answer, which is actually answered in my prior post.  Since the barrel locks up in the slide and sights are on the slide, the slide can shift (albeit very slightly) and vary in its position on the frame rail w/o adversely affecting accuracy.  But remember, the barrel has to lock up precisely and consistently in the slide.  Also the sights are on the slide, not the frame, so your sighting plane is consistent. 

So even though your slide may move on the frame, the barrel is locked on the same plane within the slide and sighted the same way.  So even if the slide is not consistent on the frame, the barrel lock up and sighting plane are.  The frame/slide fit is only responsible for the final 5% of a pistols true accuracy.  In fact, at lock up, the only thing touching the barrel outside of the slide is the slide stop pin.  The barrel does not lock up on the frame.   

To proof this, I have a Chinese 1911 Norinco.  The slide frame fit is loose and rattles pretty bad.  Out of the box at 25 yards, it would group around 2.5-3.0 inches from a rest.  I installed a Kart Match barrel and bushing and this one is practically perfect on the lock up.  I went back with the same ammo (and same loose slide frame fit) and it shot a .75" 25 yard group. 

This is why Kuhnhausen's books are considered the 1911 Bible, so to speak.

[IDescribe]

But if you have an excessive amount of 'clearance' in slide and frame fit, won't the slide potentially 'end up' in a different position... creating a accuracy issue from slide in different final location/prior to next shot than previous.

IF the slide ends up in an ever-so-slightly different position relative to the frame, no, that doesn't in and of itself affect accuracy because you don't aim from the frame.  You aim from the upper.   

Take a pistol.  Unload, clear chamber, make safe.  Remove the slide from the frame.  Put the frame aside.  The upper assembly you're still holding -- THAT is what launches the bullet.  It's the quality and fit of pieces in that assembly that affects accuracy.

The movement of slide on frame ejects spent casings and loads new rounds.

[IDescribe]

 
To proof this, I have a Chinese 1911 Norinco...

I was going to say something similar.  I've fired an old 1911 that rattled like a jar of marbles but was dead-on-balls accurate.  And I've fired an expensive, super-snug 1911 that didn't want to fire tight with any ammo.

[schmeky]

The upper assembly you're still holding -- THAT is what launches the bullet.  It's the quality and fit of pieces in that assembly that affects accuracy

That's absolutely correct.  The only exception is frame mounted sighting devices, in this case, the slide must be fitting tightly to realize the accuracy potential of the tightly fitted slide components. 

This is why a reputable 1911 smith won't recommend slide to frame tightening UNLESS you have addressed the sloppy lock-up in the slide and barrel first.  Even then, the money you spend to tighten the slide/frame is a diminishing return on a cost vs result ratio.

[JonNC]

schmeky,

How about this?

If the slide to frame fit is quite loose, wouldn't the static location of the slide stop pin, in relation to the variable slide/barrel location cause some varying tension at the lower lug?

Is there enough play in the lower lug to barrel fit to compensate?

[schmeky]

JonNC,

No.  Think of the barrel as being supported by 3 "legs", the muzzle (1), the rear of the breech and upper lugs (2) and the lower barrel lug (3).  Now think of a stool with 3 legs.  It is always solid, even on an uneven floor.  So it's not the floor (or in this case the pistols frame) that makes the barrel stable, it's the way it's supported, in this case with 3 legs.

All the lower barrel lug can do on a slide that moves from side to side is experience lateral changes in position on the slide stop pin and lower lug.  However, the lateral changes do not affect the way the slide stop pushes up or positions the barrel in the slide.  It simply can't.

On a 1911, this is regulated by the 2 lower lugs and how they ride on the slide stop.  On a CZ, the barrel is cammed into full lock up by the kidney shaped one piece lower lug.   

[JonNC]

And thus endeth the lesson!

Thanks schmeky!

[handgun2]

thank you all!

my education lesson continuous!  handguns so different than my usual interest.. SxS high quality shotguns!  double trigger man here! an all that!

anyway, thank you so much, helps me understand why I love my CZ's so much! and how Schmecky's upgrades are so helpful with trigger and yes, someday I hope to corral a 97 to add to the stable with CGW upgrades.

[nicky]

Hey Schemky,
    One day soon you will be getting mine to perform some Cajum Magic. I'll have to find another 97b first. I don't know how I will be able to be without one.