It seems there are two schools of thought on how to fit the barrels upper lugs to the slide in regards to where the barrel makes contact. Jerry Kuhnhausen recommends that lock up form a triangle with the upper lugs bearing at 12 o'clock. Others recommend a 10 and 2 o'clock position at the barrels "shoulders".
Any and all opinions most welcome on which method is preferable to the other.
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Others recommend a 10 and 2 o'clock position at the barrels
"shoulders".
If by this your're referring to the Kart Easy Fit Barrel system, it's a natural consequence of the two raised pads in the lug #1 recess of these Kart barrels which are trimmed in order to allow the gun to go to battery (with the lower lugs on the slide stop cross pin).
If that's not what you're referring to I've got no idea - or don't fully understand your question.
Thanks for your response but I'm referring to any generic oversize gunsmith fit barrel. Put another way, after the barrel is fit upwards and sufficient lug depth engagement is received, where should the barrel contact on the upper lugs, at 10 and 2 or 12 o'clock.
All around, would be my uneducated guess. But I am not that much experienced in fitting barrels.
IIRC there should be zero clearance on the sides of the lugs. The base of the barrel lugs should have zero clearance when the link pin is at the stop on the lower lugs.
I do not think the top of the barrel lugs should make contact with the slide at all.
You may need to provide clearance at the top of the barrel lugs to allow disengagement as the slide moves out of battery. A .001-.002" taper at the rear would be about all you would need while the base of the lugs would fit snug.
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...after the barrel is fit upwards and sufficient lug depth engagement is
received, where should the barrel contact on the upper lugs, at 10 and 2 or 12
o'clock.
Think I understand now. Your use of "sufficient lug depth engagement" implies you're referring to contact between the faces or the approximately vertical surfaces of the lugs - those which limit the barrel's fore-aft movement in the slide.
Those lug faces in the slide should be cut at a 0 deg 52' angle from the slide's vertical. Those on the barrel are at 0 deg 00' from the barrel's vertical.
If, after the lower standing lugs are cut, the barrel's angle matches the lug angle in the slide, contact will be evenly distributed along the faces of the lugs, as John mentioned.
But, if the barrel's at less of an angle contact will be lost at 12 o'clock and remain at the sides - perhaps 10 and 2 o'clock. If the barrel's at more of angle, contact will be lost at the sides and be only at 12 o'clock.
Don't know if any of these 3 contact patterns is a goal when fitting a barrel. I think the contact pattern eventually ends up being the evenly distributed kind as the lug metals deform and conform to each other during use.
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lugs bearing at 12 o'clock. Others recommend a 10 and 2 o'clock position at
the barrels "shoulders".
I know what you are asking... 10 and 2 is what accuracy smiths seek. Sort of. It is desirable to have upper max contact. To prevent the barrel from possibly rocking if the hard contact is at 12 o'clock I machine a small clearance flat at the 12 position. This gives the barrel a "three legged stool " or "V" block stance. No wobble. Two solid points of contact at the upper lugs and one solid contact area on the lower lugs. This creates a very stable position for the barrel. This of course is enhanced by a very closely fitted frame and slide. Consistent repeatability...
Guess I somehow misread the OP and led myself to think he was referring to contact between the vertical surfaces (lug faces).
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To prevent the barrel from possibily rocking if the hard contact is at 12 o
clock I machine a small clearance flat at the 12 position.
Is this flat at the tops of the lugs or at the bottoms of their recesses?
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Jerry Kuhnhausen recommends that lock up form a triangle with the upper
lugs bearing at 12 o'clock. Others recommend a 10 and 2 o'clock position at
the barrels "shoulders".
Ben, since this doesn't seem to make any sense whatsoever (to me), could you point me to the volume and page number where Kuhnhausen says that?
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Is this flat at the tops of the lugs or at the bottoms of their
recesses?
It's in the bottom of the recess. Doesn't take much, about .008/.010 inch.
Most match grade barrels run about .070 thick in that area, so it is not a problem.
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It's in the bottom of the recess. Doesn't take much, about .008/.010
inch.
Nifty idea! That'd make a flat about 0.16" wide directly above the 0.36" wide feet for a nice "anti-twist" feature.
That is exactly what I wanted to know. Thank You!
Hawkmoon; I'll get the page number(s) out of Vol. II when I get off work.
Don't want to hijack Ben H's thread (too much, anyway) but does anyone think shims (maybe silver soldered to the frame's lug clearance slot) would also help fix the position of the aft end of the barrel?
PICTURE 404
Maybe the 0.008" or so of total play in that area is necessary for proper & reliable operation - I don't know.
Take a look at pages 130 thru 134 in Volume II and you'll find the discussion and drawings of Jerry's recommended 12 o'clock contact position.
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does anyone think shims (maybe silver soldered to the frame's lug clearance
slot) would also help fix the position of the aft end of the barrel
This area is addressed by accuracy smiths. When machining the frame for a ramped barrel, such as the 9mm distinguished and long slide open class guns, this dimemsion is controlled by the milling process and held to close tolerances. Unramped barrels are tig welded on the lower lug sides and remachined to what ever dimension is needed to make the fit. This is usually only necessary on older mass produced frames, which are not really used much anymore by serious accuracy builders. The newer match frames of today, are held to tighter specs in all areas. Some of the barrel makers are also oversizing the lug area somewhat to allow for and aid in precise fitting..
This is a crucial area to minimize barrel twist. The lower lugs standing on the cross pin cannot be expected to controll the barrel in a torque moment. The stance footprint is too narrow. Their job is to position the barrel vertically, and repeated, uncontrolled torque stress on the lower lugs will ruin the best fitting job. Years ago the old time smiths would silver solder a small block in the upper rear left side of the ejection port and closely match it to the contour of the barrel. This also would aid greatly in controlling the twist/torque of the barrel. Many think that a closely fitted hood will do this. It will not. Again, too small of a contact area, and like the lower lugs in a position of leverage disadvantage.
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Years ago the old time smiths would silver solder a small block in the
upper rear left side of the ejection port
Would that be the left side as viewed from the front or as viewed from the rear of the gun?
Would that be the left side as viewed from the front or as viewed from the rear of the gun?
How close should the sides of the hood be fit on an accuracy job? I've heard two schools of thought on this as well; fit to where there is no visible gap along the sides and, leave .003 to .005 side clearance.
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How close should the sides of the hood be fit on an accuracy job?
Each gun has its own set of variables. Ideally, I like to set the hood dimension as close to zero as possible. But as the slide closes and the barrel is moving into battery, there is a condition of unsupport. The barrel can be moved slightly from various vibrations,etc. and the corner edges of the barrel hood may not make perfect alignment with the slide recess and cause a bumping or momentary hitch in the action as it closes. If all specs are tight and in alignment, a very tight clearance can be run. Otherwise, the clearances will need to be larger.
[This is another testimony for yesterdays discussion about why lower lug clearance is important, and how it can assist in top end alignment.]
I cut a generous 45 degree angle on the corner of the hood to aid in offsetting any misalignment during the firing cycle. I also cut a corresponding angle on the slide recess. When cycling the action, you should not be able to detect any glitches, bumps or thumps as the barrel moves into its locked position. I tend to set things up very tight, fire the gun 100 rounds or so, inspect the internals for witness marks, and adjust accordingly.
Before touching the barrel, square up the recess in the slide. I do it by hand and use gage blocks to get it sqaure and true, smooth and polished so that the gage block is a perfect fit. Then fit the hood to the slide.