Barrel Torque

[Herb Clark]

Several (OK, six - sorry) Novice questions: 1) During bullet travel down the barrel a torque is generated - what surfaces resist this torque and maintain barrel alignment (sides of barrel hood?, upper barrel lugs?, lower lugs seated against slide stop pin? or a combination of several of these). 2) In battery, should I be able to see light on both sides of the barrel hood? 3) Should the slide stop pin show any link wear - my Gold Match doesn't, my Para shows some on the bottom - by wear I mean shiny. Both pistols have over 10K rounds through them 4) What diametrical clearance should exist between slide stop pin and link? Slide stop pin and frame? 5) what side clearance should exist between lower barrel lugs and frame? 6) In battery, what surfaces of the upper barrel lugs are suppose to be in contact with the frame?

Sorry for all the questions - I'm trying to learn - the Technical articles on Timing and Operation were a mite confusing in several places! Thanks ya'll!!!

[1911Tuner]

Wow...That's a buncha questions! Welcome aboard, Herb.

Barrel torque is allowed or resisted by how well the barrel fits. Rather than try to answer each question, I'll describe the fitting points. Basically, nothing means everything, but everything means something. To simplify things, I'll describe a hand-fit barrel instead of a drop-in or ordnance-type fit.

The barrel is cammed up into vertical lockup by the lower lug and slidestop crosspin. The depth and fit is determined by the distance from the crosspin hole in the frame to the tops of the lug slots in the slide...and the dimension from the lower lug feet to the tops of the barrel locking lugs.

The upper barrel lugs are engaged horizontally by the distance between the slide face...or breechface...to the rear faces of each lug and the distance
between the front faces of each barrel lug and the rear face of the barrel hood. The upper barrel lugs don't contact the frame.

The sides of the barrel hood fits closely in its recess in the slide, but shouldn't actually touch. There should be a little clearance. Depending on what the gun is built for...and by whom..(All smiths have their own methods
and criteria)...there should be anywhere from a half-thousandth inch per side to .005 inch per side. A gun built strictly for 50 yard Bullseye competition
generally has tighter clearances than one built for IDPA/IPSC games...and those in turn are usually a little tighter than a gun built for duty carry or general purpose use.

The barrel bushing to slide clearance is usually anywhere from finger-tight with little or no discernable play all the way to requiring a bushing wrench to turn it. Bushing to barrel clearance varies too, according to what the gun is intended for. Bullseye guns are fairly tight, with as little as a half-thousandth inch clearance to as much .003 inch for carry...and anything in-between...as long as the barrel doesn't spring back when pressed into battery position in the slide, you can usually get away with it being pretty close. As little as .001 inch can be used even in a carry gun if the pistol is otherwise well-built. Many guys like to have things a bit looser for carry or duty guns, and
.003 inch here isn't too much. Most production guns are looser than that, going as loose as .005 inch or more.

My personal criteria for clearances on a carry gun are fairly tight without
approaching target or match-grade too closely. .003 inch clearance on the sides of the barrel hood and between breechface and rear face of barrel hood. Finger-tight bushing to slide and .003 inch bushing to barrel. I like full depth of vertical lug engagement and no less than 90%. I like for at least two lugs to engage horizontally, and prefer three. I like for static headspace to be about .900-.903 inch and no more than .905 inch. Range beaters get a pass with as much as .910 inch, and any that are over .912 are rebarrelled.

Slide to frame fit, I like to see .005 inch or less in both planes, and like .003 better provided the slide will make full travel on the bare frame under its own weight when dry. If the gun is to be carried, I include the barrel and slidestop...and the gun must move into and out of battery under gravity alone by tilting the pistol muzzle up and down at 45 degrees.

These things strike a good balance between useable accuracy and dead-nuts reliability under adverse conditions, whether the pistol is clean or dirty...dry or dripping with oil...with any decent quality ammo.

If you're mainly interested in building a match or Bullseye gun, you may want to pose your questions to Bob Brown...username robot...here on the forum,
as well as George Smith of EGW...also on-board as a member. Those guys are
the builders of wicked accurate match-grade guns. Most of my work has been in either rebuilding older, worn pistols, or tightening newer ones that were a little too loose for my tastes and purposes. Reliability tuning, troubleshooting, and the like for duty or carry guns has been my main focus.

Luck!

[Herb Clark]

Thanks 1911Tuner - not trying to build, just trying to learn how the 1911 works and be able to look at mine to see where there is a problem. You stated small clearance between breech face and hood (at battery) so I'm assuming that when slide drives barrel forward by pushing on hood, at lockup there is a clearance (very small between hood and breechface) and the forward-aft movement of barrel is resisted by the rear of the top barrel lugs and the front of the lower lugs.
If the above is true, while in battery, the link should be "loose", consequently link clearance to slide stop pin isn't critical to barrel location/accuracy?
Last question for today: What should diametrical clearance of slide stop pin to frame is required - i'm thinking this is important to locate on lower barrel lugs properly. Finally it looks as if barrel torque is resisted by camming action of slide stop pin on lower lugs and friction of upper barrel lugs to slide (vertical camming force resisted by top of barrel against slide, not top lugs).
Hope I'm not a pest!

[1911Tuner]

Howdy Herb,

I may have to answer this one in two parts...Dog feedin' time and I've got 13 of'em.

The link shouldn't have any effect on vertical lockup, though due to the design of the radius at the rear of the bottom lug, it will be in light compression when the gun is in full battery unless the lug is badly out of spec.
When the link does push the barrel into vertical engagement, the condition is known as "Standing on the link" which isn't conducive to good accuracy...and can cause the slidestop pin hole to wear prematurely, and wallow out the
upper link pin hole in the lug. many factory barrels do stand on the link and/or ride the link into battery...but it's not correct.

Slidestop pin hole in the frame is within spec at .201 + .002 inch/-zero.
Slidestop crosspin is spec-ed at .198-.2005 inch but you may find many factory pins as small as .195-197 inch...which means that the clearance can be as much as .007 or maybe a little more. Most factory slidestop pins run about .198 or so. Most aftermarket pins are at the high end of spec at .200 inch.


Gotta git! Be back later.

[1911Tuner]

Herb,

This may help you gain a little understanding before we get too deep into your other questions.

http://forum.m1911.org/showthread.php?t=6910