Thought I would show a perfect example of what I have mentioned in the past regarding the matching of barrel/slide radii.
My photo skills are limited, but if you look closely, you will see that this barrel slide combination, which has thousands of rounds through it, only makes contact on one side of the radial lug. There is zero contact on the other. This is a very common condition. Not a tragic situation for most G/P guns, but not good if you are after maximum accuracy. It is neither the barrel nor the slide which is at fault. It shows the need to adjust both radii to match.
I included an old three digit Baer frame for amusement.
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Thanks, I was wondering about that just the other day. I have a bull barrel that I'm fitting and when I smoke it up and give it a tap with the barrel centering tool on I don't have any contact at all. It won't be any great loss in this gun as it is just a beater truck gun, but it had me wondering.
Looks like a lot of contact on the left or "drivers side" of the barrel. Assuming a gunsmith fit barrel with over sized lower lugs, wouldn't the solution be to remove metal where it contacts on the left side so the barrel fits higher into the slide and makes contact on both sides of the barrel? Obviously this can't be done on this barrel as the lower lugs have already been fit. Was this an oversight during the original fitting, or is the mismatch between the barrel and slide so much that it can't make contact? I'm not trying to be negative towards who ever fit the barrel, just curious as to why it is the way it is.
That barrel is out of the Baer frame. It is a very early gun, three digit that is well under 100. It's impossible to say who fit the barrel, as it has been thru several owners, but it is not a bad job. The gun shoots quite well. I am not replacing the barrel. It needs a firing pin upgrade to 45.
It's very common to find barrel / slide combinations that don't match. Some are impossible to get equal contact on both sides. Old Colts are especially prone. The two radii have to be compatible, and close to the same axial center. If the slide radius is .351, the barrel lug radius must also be .351 ... most are not.
The first picture is first touch... it lacks .005 of being the same radius as the slide lug, at a depth of .048 lug engagement. The second picture is true radius at finish depth..
Jerry do you mind showing how you measure slide radius and axial center?
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Jerry do you mind showing how you measure slide radius and axial
center?
I lap the slide bore to true the radius. Usually .001 /.003 will true them up.
Now I have a known dia.
When turning the barrel lug, the lug radius is kept concentric with the .699 dia. (or what ever it happens to be) That may seem obvious, but the barrels are never true and concentric in all dimensions. having the lower lugs and barrel bushing on C/L is also an important element.
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"but the barrels are never true and concentric in all dimensions."
Jerry: I found this out the other day when setting up a Schuemann barrel. Since I don't have a DRO on my lathe, I decided to cut the radial lugs on my Bridgeport. I held the barrel in a 5C collet in a square block, held the square block in my toolmaker's vise attached to my rotary table. I indicated in the barrel then raised up the collet holder .050"/.045" and cleaned up the lugs to match what I measured the slide lugs to be.
My only dilemma was what to use for the barrel datum. The short chamber T.I.R. was over .005" out of agreement with the barrel OD. I figure the piloted reamer will follow the short chamber to a certain degree, I use a Manson floating reamer holder in my lathe. I chose to use the OD for a reference, but I'm curious if you have any comments. This is not a bullseye gun, but I still want to do as good a job as I can.
Yes; good job BZ. The OD is what will mate with the slide ID. If you look at my barrel, I have taken a truing cut just in front of the lugs after zeroing the .699 OD. The .699 OD is .004 out of TIR with the .580 barrel dia. This light cut gives me an easy constant to refer to as I offset the lug depth and keep the set up on zero.
This barrel had lots of extra stock in the chamber. Both short and small; a gunsmith's dream. It too was .005 out of TIR with the bore line. It had enough stock to take a light single point truing cut for the reamer to follow. This is unusual and many barrels are--pot luck/ "you have what you got".. This barrel shot an awesome 30 round group yesterday from the Ransom Rest with 27 rounds in a 1.150 inch group C/C.
kl; No the only contact is the visible shadow on the one side.
Irish lad;The Baer was having light hits, not uncommon with 45s and the little pins. The big pins not only solve the problem, but tend to aid in tighter groups.
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It had enough stock to take a light single point truing cut for the reamer
to follow.
Brilliant! It never dawned on me that I should try and take a dust cut with a boring bar prior to reaming. I can't tell you how much I've learned looking over your internet shoulder. When I saw your spider setup the other day I realized how much there is in undocumented knowledge out there in spite of how much folks like Jerry K. have tried to put down on paper.
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I have a stupid question regarding the radial contact. What do you believe
is the best way to fit the rear recess of the barrel for proper fit?
Here's a crude sketch. I strive for as much contact as I can get. Hence the effort taken to match the radii. It has worked quite well, and I get nearly full half circle. I grind a shallow flat at 12 o'clock to create the "three legged stool effect". The more contact, the bigger the feet on that three legged stool.
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Good info. I finally gave up trying to file and took some of the strips of emery cloth in various grits, cut them down to the same width as the groove, put the barrel in between a set of radiused padded jaws to hold the barrel in place, and then worked the emery cloth strips, checking the contact and barrel position, such that I got an "Even" fit that showed wear and lockup with the slide over as much area as possible. Basically, threw some dykem blue on it, checked for rub, sanded, checked position and rub, sanded, then when I was close, switched to the ultra-fine grit cloth and polished until I had it where I wanted it with good contact.
I'm sure that's the wrong way to do it, but it seemed to work OK for me.