Trubor barrel fitting issues

[RippinSVT]

Hey guys, perhaps this should be in the gunsmithing lobby, I dunno.  I'm building my first full ground-up open gun and I'm fitting 2 barrels, one in 9mm and one in 38SC.  Anyhow, I started last night and I made my 1-degree cut on the front of the slide, followed by fitting the 38SC barrel hood and cone comp.  I took a few light passes in my lathe at the back of the comp to get the slide/comp clearance I wanted, and got it locking up smooth and firm.  Next up was the 9mm Trubor barrel from Brazos with the Thundercomp II.  The barrel dropped into the rear hood recess with only a few file swipes on each side, and it became clear that I was never going to get initial lockup unless I took several thousandths from either the slide or the comp to allow the barrel to move back towards the first lug.  Having already fit the 38SC barrel, I chose to turn the back of the Trubor comp down on the lathe, maybe .020".  I don't know if this is kosher, but that's what I did.  Some measuring and file work at the rear of the hood and I had lockup.  Here's my issue as it stands: I've fit several barrels into some highly accurate guns (like 1" at 50yds), and never had to remove a lot of material from the barrel lug recesses to get firing pin alignment and .045" lug engagement.  The hood is not binding on the breachface but is touching.  The comp appears to have 004"-.005" clearance with the slide as well. Currently I only have about .027-.030" upper lug engagement with the Trubor barrel in the CK Arms slide, whereas I have almost .050" with the other barrel (Kart).  Has anybody else found the Trubor barrels to be very oversized on the upper recess radii, or should I look elsewhere for my impedence?  I'm gonna get the modeling clay out tonight and do some more checks, but I found it extremely strange that the Trubor wasn't particularly oversized at the hood and yet I possibly need to file .015" off the lugs.

Edited September 21, 2017 by RippinSVT

[RippinSVT]

Doing a little more thinking on this, and I'm wondering if I could have some vertical binding or springing in the bull barrel flare near the muzzle.  Pretty hard to tell with this permanent comp.

[Aircooled6racer]

Hello: Did you measure the depth of the lugs on the barrel? You most likely have springing on the barrel or not enough clearance in front of the lugs. Thanks, Eric

[RippinSVT]

I did but I can't remember offhand. 

[stardust tommy]

for fitting a barrel I use soot (papertape or carbid/oil lamp) to check for bind, always wipe it of and aply new soot. it wil build up a thicker layer. (this method is used by the master gunsmith here in Liège, FN Herstal)

 

get a good chamfer on the al the corners of the barrelhood,

on my last Trubor barrel I had a high spot in the first lug of the barrel

I also stone/break te corners of the barrellugs (verry little)

I had a trubor barrel that made contact ont the unther side up front in the slide

I had one slide with a burr on the inside rounded part where the barrelhood would fit

 

this is a summary of problems I ran into

 

 

[RippinSVT]

2 hours ago, stardust tommy said:

for fitting a barrel I use soot (papertape or carbid/oil lamp) to check for bind, always wipe it of and aply new soot. it wil build up a thicker layer. (this method is used by the master gunsmith here in Liège, FN Herstal)

 

get a good chamfer on the al the corners of the barrelhood,

on my last Trubor barrel I had a high spot in the first lug of the barrel

I also stone/break te corners of the barrellugs (verry little)

I had a trubor barrel that made contact ont the unther side up front in the slide

I had one slide with a burr on the inside rounded part where the barrelhood would fit

 

this is a summary of problems I ran into

 

 

 

Thanks Tommy.  I too always break and chamfer the edges of the lugs and hood. I will use soot and particularly look for contact towards the front of the cone, top and bottom.

[Broncman]

Get some Dykem. I just fit a Brazos Thundercomp Trubore to a CK slide. There was springing, had to polish the barrel some in the right places.

 

I also had a high spot in the first recess of the barrel lug but still had 45 thousandths engagement.

Edited September 21, 2017 by Broncman

[RippinSVT]

2 hours ago, Broncman said:

Get some Dykem. I just fit a Brazos Thundercomp Trubore to a CK slide. There was springing, had to polish the barrel some in the right places.

 

I also had a high spot in the first recess of the barrel lug but still had 45 thousandths engagement.

 

Thank you. Did you have to remove several thousandths about 3/4" back from the comp? That seems to be my major contact area. My first lug recess on the barrel is .046" at 12-o'clock but I may need to take a little off at "10 and 2" as well. The black soot seems like the hot ticket on the barrel cone contact.

Edited September 22, 2017 by RippinSVT

[Broncman]

Yep, 10 and 2 about 3/4" back.