STI trubore barrel

[stardust tommy]

Hi

I'm building an open 9mm major with a 9x19 trubor barrel

I know that I have to finish ream the chamber, but do I need to enlarge the freebore for 9mm major or has the factory barrel the correct freebore?

triggerparts installed + safety (STI sear +disco, C&S hammer, EB safety-

some machine work done

gr

Tom

Edited December 8, 2013 by stardust tommy

[Jediwarrior]

The factory barrel has little or no freebore.

The Manson or Clymer chamber finisher reamer will cut the freebore.

If you want a longer freebore, then buy a throating reamer to lengthen the freebore after cutting the chamber.

I don't know if you need to lengthen the freebore for 9mm Major, but from my experience, the chamber reamer works fine in itself.

Edited December 9, 2013 by Jediwarrior

[lcs]

Loaded out to 1.170 and never had any problem with STI TRUbor barrels. Unless you have old style SVI mags that allow longer OAL as mags with spacers limit your OAL. (Had several new Open guns and replacement Trubor barrels.

Try it before you waste your money and time.

[stardust tommy]

thanks for the info!

gr T

[Jediwarrior]

Hi Tommy,

A bit off topic, but what was the depth of the Horizontal Impact Surface (HIS) on your new build? This is the distance from the top of the frame to the bottom of the feed ramp. This distance for STI frames varies from 0.295 in. to 0.305 in.

There should be a minimum of 0.010 in. clearance from the top of the barrel and the inside top of the slide.

If cut too deep, you could have cycling problems in the future as the barrel drags on the inside of the slide at the 8 and 4 o'clock positions.

Schuemann's instructions of a depth of 0.315 in. is wrong.

Edited December 10, 2013 by Jediwarrior

[Meat Target]

Hi Tommy,

A bit off topic, but what was the depth of the Horizontal Impact Surface (HIS) on your new build? This is the distance from the top of the frame to the bottom of the feed ramp. This distance for STI frames varies from 0.295 in. to 0.305 in.

There should be a minimum of 0.010 in. clearance from the top of the barrel and the inside top of the slide.

If cut too deep, you could have cycling problems in the future as the barrel drags on the inside of the slide at the 8 and 4 o'clock positions.

Schuemann's instructions of a depth of 0.315 in. is wrong.

For my STI 38super with the Trubor full ramped barrel the distance from the top of the frame to the bottom of the feed ramp cut came out to .321in. with 0.010in clearance at the top with slide stop pin in. That leaves also about 0.010in. clearance under the ramp at full link down.

I have about two thousand rounds through the gun so far without any problems. I don't thinks the depth of the cut its all that critical as long as the barrel is impacting the vertical surface. If there is 0.0005in. or 0.050in. clearance under the ramp I don't see how operationally the gun would know the difference other than reducing the vertical impact surface area a little, but you need to radius the top edge anyways.

I also found that with STI frame and Trubor barrel combo you need to do a little clearance cutting at the top of the frame to get the barrel to link down enough.

Everyone has their own way of doing things, I just like to put a little extra space under the ramp to leave a clearance for gunk buildup.

Sorry for the highjack back on topic:

What Jediwarrior said, just get the Clymer reamer you most likely will not need to lengthen the free bore unless you want to play around with reducing peak pressures or something.

[stardust tommy]

hi

this was a frame for a non ramped barrel so I milled the slot myself, the slot was .300 deep

I have not fitted the barrel yet, still waiting for a replacement mill for my Nowlin frame bridge cutter, it was delivered with a wrong endmill

thanks for the input!

[Jediwarrior]

Hi Meat Target,

This is another area where it can be an art.

If the HIS is too deep, then the barrel will rest at the remains of the barrel bed, which are the two curved surfaces on either side of the frame. Over time, say about 20,000 rounds, these 2 contact surfaces will compress, causing the barrel to go further down. If it goes down too much, then the barrel can start to drag at the 8 and 4 o'clock positions inside the slide.

So, in the end, the barrel may or may not drag depending on the limit of the compression and the location of the barrel channel relative to the fame.

I have seen raceguns go bad at these high round count and the result will be erratic and weak ejection, and the occasional FTE. So, I had to TIG weld the HIS, adding 0.005 to 0.010 in. in height to solve the problem. Full contact with the HIS will prevent this possibility from happening.

Edited December 11, 2013 by Jediwarrior

[Jediwarrior]

Here is a picture of a barrel with severe drag marks at the 4 o'clock position. The grey line above the number is a shadow cast on the mark by carefully angling the barrel.

Again, this process takes time, and may or may not cause malfunctions in the end depending on several factors.

In this case, TIG welding the frame was the solution.

Edited December 11, 2013 by Jediwarrior

[Meat Target]

Jediwarrior,

I understand your concern but I just go about it a different way to get the same results.

I like to fit the frame and barrel to have the low lug impact the Vertical Impact Surface instead of the horizontal surface (Schuemann barrel fitting method). It will stop the barrel in the same place in link down as if it hit the horizontal surface but doesn't put as much stress on the link and slide stop pin. The barrel will not contact the frame at 8 and 4 o'clock which can be verified as I don't have any marks on my barrels as shown in your picture.

As I had mentioned I do sometimes need to remove material on the top of the frame (4 and 8 o'clock contact area) for the barrel to link down enough and get 0.010 in. clearance with the upper lugs. It just turns out with some combinations of barrel, frame and slide fit there isn't enough clearance otherwise.

As you said its an art, no to guns are the same and if its running ok go with it.

[Jediwarrior]

Hi Meat Target,

I think you misunderstood me. We both 100% agree that the VIS is absolutely essential for a good fit. This is exactly what Schuemann was referring to in his instructions. That way there is no stress on the link and slide stop pin. The VIS stops the rearward movement of the barrel.

What a lot of people don't realize is that the barrel also links DOWN, and that there has to be a surface area for it to contact and stop.

In a non-ramped barrel, that surface area is the barrel bed. In a ramped barrel, ideally it's the HIS. We make this distinction as the HIS is horizontally flat, while the barrel bed is curved.

Edited December 14, 2013 by Jediwarrior