barrel fitting

[Bill Hale]

I'm trying to fit a Kart hard fit barrel to a High Standard 1911A1. The barrel is finish chambered so, as I understand it, the first thing to do is to equalize the barrel lugs, i.e., make the barrel lugs spacing match the slide lugs. How do I measure the slide lugs? Kuhnhausen recommends Cerrosafe (something else to order from Bownell's) and measure from front edge to front edge. I only have a dial caliper. Measuring from front edge to front edge would be an eye ball affair. Obviously, I'm not a machinist. Is there another way?
Also, the barrel measures from recoil face to lugs, 1.151, 1.473 and 1.800. Is lug 2 at 1.473 too short? Kuhnhausen shows 1.476. I would like to have all 3 lugs in play, but don't want to get too much head space.
I'm probably in over my head, but have wanted to try this for a long time. Any help would be appreciated.

[Joni Lynn]

I can't help you with most of your questions...........actually not with any of them.
While the barrel may be finish reamed many Kart barrels are a bit snug in the chamber and might require just a touch to open them up a bit. A couple of mine did.

[Bill Hale]

Another item to order from Brownell's, a finish reamer. I was hoping not to have to buy one.
Thanks, Joni Lynn.

[Joni Lynn]

When firing jacketed bullets it isn't very noticeable, but with my lead loads the gun will fail to return to battery in pretty short order. I asked a 'smith and he informed me that often the chamber needs relieved a bit.

[bushka]

You have the instructions in vol2 manual correct?
You could use dykem blue and a lug file from brownells in repeated trial fits,and because Ive never done barrel fitting before,but am a machinist,this is how I would do it.
The idea is that the dykem blue [not prussain blue] dries like nail polish,and you would want at least the 2 rear lugs to show bearing marks when reassembled and locked up,and disassembled again.

[1911Tuner]

Well...First you've got to be able to measure the distance from the breechface to the rear face of each slide lug...which requires either a single adjustable fixture, or three separate fixtures. I've used barrels and shim stock or feeler gauges for the task. Not as precise as an adjustable fixture...but workable.


Then, you measure the distance from each front barrel lug face to the unaltered hood face, and check against the slide measurements to determine
which lug or lugs would come into play if the hood was cut to just let the barrel engage with the slide.

Let's say that you have to remove .010 inch from the hood to get the barrel in...and that .010 inch coincides with the distance from the breechface to the first slide lug. Okay...You've got horizontal bearing on the first lug.

Measure from the hood face to the second barrel lug. Does the distance match the distance from the breechface to the rear face of the second slide lug? If it does...you've got lugs 1 and 2 in the game. If the distance is .001 inch short, you've got that much air between the lugs, and #1 is preventing #2 from touching. If it's .001 inch LONG...#2 is bearing, and it's keeping #1 from touching.

Check #3 in the same way.

If your fit is allowing #1 to touch..with 2 and 3 kissing .001 inch of air...shoot the gun. #1 should deform and set back .001 inch within 500 rounds and equalize the lugs. .002 inch should allow equalized lugs within 1500 rounds or so...and within another 500 rounds, they should be fully seated.

If 1 and 2 are bearing, and #3 is kissing .002 inch of air...you'll probably never get it to touch before you wear the rifling out of the barrel. If 1 and 2 are bearing, and #3 is .001 out...it'll probably take 15,000 rounds to equalize, and a little less if 1 and 3 are bearing, with #2 .001 inch out. More ammo will be required if you shoot mostly cast lead bullets.

Whatever amount of lug deformation and setback occur during the process of
fire...or pressure equalizing will be the amount of headspace that is added...so if you start with a static headspace dimension of .900 inch, by the time the lugs are fully equalized, that number will be about .902-.9025 inch, which is still a far cry from the .920 maximum.

Trying to pressure equalize lugs with more than .0015-.002 inch of airspace is pretty much a waste of time with today's hard slides and barrels. It will eventually occur with normal wear...but it'll take a long time. Filing the barrel lug faces to get the dimensions within that magic .001 inch is the way to go, but it does require patience and skill with the file to prevent cutting the lugs
at an angle from side to side. Due to the barrel's tilt into the slide, the lugs will probably start to seat at the lower area first, and "come in" toward the top with use, and become fully seated and equalized.

Because the barrel tilts at the rear, vertical depth of engagement will be greater on #1...a little less on #2...and the least on #3. Depending on how far the barrel tilts when tightly engaged vertically...the actual figures will vary a little from gun to gun...which is why it's not a major issue if 1 and 2 are engaged horizontally, and leave #2 in the breeze. #3 offers the least engagement strength. Nice to have it lend a hand...but not all that critical.

Even if you only have #1 horizontally engaged...as long as it has full vertical depth, or is at least 95% vertically engaged...the gun will last a long, long time as long as you stick to mostly standard-pressure ammo, reserving the hot-rod stuff for testing and carry duty. Using reduced pressure levels for the majority of your shooting...especially if you use it with cast bullets...you can go broke handloading enough ammo to cause enough deformation and increased headspace to be a concern. 230-grain cast bullets loaded to 750-770 fps will probably take upwards of 75,000 rounds to do it.

[drummer]

Would an inside caliper such as this (http://www1.mscdirect.com/cgi/NNSRIT?PMPXNO=5737302&PMT4NO=0)
work to measure the distances from the breech face to the rear of the slide lugs?

Maybe George at EGW could make an adjustable version of his barrel fitting gauge to take those measurements.

[1911Tuner]

Would an inside caliper such as this (http://www1.mscdirect.com/cgi/NNSRIT?PMPXNO=5737302&PMT4NO=0)
work to measure the distances from the breech face to the rear of the slide lugs?

Maybe George at EGW could make an adjustable version of his barrel fitting gauge to take those measurements.

Possible...but any deviation in the angle would throw the measurement off.
If you measured each one several times...practicing until your readings were pretty consistent...and then take an average of three careful readings...you could get to within a thousandth of an inch or so. What that equates to is a tolerance of +/- .001 inch per lug...for a possible error of .006 inch from the first lug to the third...and up to .004 inch between any adjacent pair.

Better to use a fixture designed specifically for the job, in any event. Much more repeatable in locating to the same place each time.

[Bill Hale]

Tuner,
Since I don't have an adjustable fixture, what do you think of Kuhnhausen's method of using Cerrosafe?
Thanks, by the way, for being so generous with your time. (+1 on you writing a book.)
I won't be back online 'til tomorrow, time for church tonight.