Gunsmithing For guys that have done DTA SRS barrels, looking for your input.

[Supersubes]

Never chambered a barrel for one of these before, and the last time I handled one of these may have been at SHOT show the year they were introduced. I just bought one from the eurooptics sale and I’ve been poking around it a bit To learn about it.

I’ve searched for drawings of the breech detail unsuccessfully for quite a while. There are some old threads on it, but the drawing pics are gone. Surprisingly little conversation about doing these barrels.

So it looks like the chassis barrel clamp doesn’t do any clamping on the extension itself just based upon where the clamp ends, and the fact that the extension is undersized slightly(1.243”). I put the barrel in the lathe, because I was curious about the alignment between the shank, extension, and chamber. I found that the shank and extension were perfectly concentric, and the ass end of the chamber was out by .002(total).

So here’s my question. With bores and barrels being how they are, there’s a real likelihood after chambering/threading that the extension isn’t coaxial with the shank of the barrel, which would be bad for all sorts of reasons. Seems like another operation would be needed to true the shank of the barrel to the extension. Also seems that in order to have material to make that truing operation, the barrel needs to start out slightly over 1.250, which may involve an upcharge depending on who’s making the blank.

What are your thoughts? This has been a curiosity of mine for some time, I’d appreciate your input.

 

[Quickshot]

I think you need to check the extension and barrel separately. The face of the extension and the barrel shoulder are the alignment surfaces.

1) The threads should have enough clearance to allow the two surfaces to mate.

2) The extension’s face needs to be parallel to the extension’s bolt lug abutment.

3) The barrel’s shoulder should be aligned to the chamber.

Verify those three features. Perhaps one of them will be the root cause of the misalignment.

Cheers,

 

[Supersubes]

I think you need to check the extension and barrel separately. The face of the extension and the barrel shoulder are the alignment surfaces.

1) The threads should have enough clearance to allow the two surfaces to mate.

2) The extension’s face needs to be parallel to the extension’s bolt lug abutment.

3) The barrel’s shoulder should be aligned to the chamber.

Verify those three features. Perhaps one of them will be the root cause of the misalignment.

Cheers,

Thanks for your input. Not trying to solve the crooked chamber in the current factory barrel. More looking for the methods you guys use for DTA barrels when you fit them. I chamber typical bolt actions with the bore dialed in, and the entire tenon and chamber are cut in one setup, probably like most do. That should most likely lead into some misalignment in a DTA if the bore is off center and curved.


I spoke to someone today, who does lots of these, and has a good reputation. Essentially he explained that the threads and shoulder are cut with the barrel exterior dialed in, so the extension is straight, and all the bolt lugs will contact equally, etc. Then the bore is dialed in and the chamber is cut. Of course the chamber is slightly crooked to the bolt face in that case. I’m betting that’s exactly why the factory barrel is the way it is.

 

[Quickshot]

Sorry, I miss read your question. I believe the barrel shank should be turned coaxially with the chamber; after the chamber is dialed in. The issue is the extension is cut to receive the chassis lock cam and it would be nice to keep the lock aligned to the chamber. The extension should be machined in a fixture that uses the chassis lock groove as the registration feature. So, the extension should be true.

I agree using typical single step process; the barrel’s virgin shank will not be concentric with the bore at the chamber throat. So, a second operation is required to true the barrel shank and chamber.

All the DTA rifles I have seen shot well. So, maybe the chassis design can tolerate the barrel shank misalignment.

Cheers,