Gunsmithing Adding a shoulder

[Tgunz64]

Is it hard for most gunsmiths to add a shoulder to a barrel? Getting my 22-250 threaded for a suppressor but didn’t realize it needs to be .600 od. Mine is .566. Came across a place online that does it. But my gun is already at the smith but closed for the holiday so figured I’d ask here.
Thanks!

 

[GH41]

It could be as simple as using a precision ground washer. I'd start with one of these turned to the OD you want. https://precisionarmament.com/product/replacement-accu-washer-shims/

 

[gnochi]

Adding material is generally more difficult than removing material, yes. A thread-on nut that locks onto a taper would probably work fine though.

You also have options of using a clamp-on adapter or a muzzle-indexing adapter, instead of a shoulder-indexing adapter.

 

[GH41]

Do what? Clamp on is a fucking joke! Crawl back into your hole!

 

[gnochi]

Since the peanut gallery could get you killed, I’ll go into more detail.

Fundamentally, you need to apply a load along the barrel to hold the suppressor in place, and align the suppressor. The sliver of barrel that would be left of the shoulder after threading is not sufficient to do so. Washers don’t do squat about that - they spread a small amount of the total load when there is additional backing material to spread the load into. Air is not a sufficient backing material.

There are only a handful of choices that will result in a safe rifle:

1. Make a new barrel that has enough diameter slightly back from the muzzle to support a suppressor.
2. Cut back your barrel until the diameter slightly back from the new muzzle is large enough.
3. Apply the load semi-radially. You can do this with a taper-fit nut, or a clamp-on adapter like this: https://www.wittmachine.net/custom-clamp-on-threaded-adapter.html
4. Apply the load at the muzzle instead of the shoulder.

Regardless of which method you choose, you will need to check for clearance to your suppressor baffles.

Clamp on adapters are almost always slightly out of alignment - the bore and outer surface of the barrel are never perfectly concentric - so this check is more likely to catch an issue with a clamp-on adapter. However, provided you have clearance to avoid baffle strikes, bolts are torqued appropriately, and the surface finishes of the barrel and clamp interface are compatible, this is as safe as anything else involving rifles. They aren’t particularly elegant, but they work.

 

[jetmd]

GH41, how do you feel about this?

 

[Tgunz64]

I’d hate to cut the barrel back but do you think I’d lose a lot of accuracy if it had to be cut 2”? If so it would leave me with a 20” barrel. Not sure how far up the barrel I’d have to go to get the .600. Again my gun is at the shop waiting to be threaded. I can call Monday and have the smith see where he gets that measurement. But I talked with him yesterday and the shoulder would be .577 where the threads would end. Want to use the 419 Hellfire mount.

 

[Huskydriver]

I’d hate to cut the barrel back but do you think I’d lose a lot of accuracy if it had to be cut 2”? If so it would leave me with a 20” barrel. Not sure how far up the barrel I’d have to go to get the .600. Again my gun is at the shop waiting to be threaded. I can call Monday and have the smith see where he gets that measurement. But I talked with him yesterday and the shoulder would be .577 where the threads would end. Want to use the 419 Hellfire mount.

Barrel length has 0 percent effect on accuracy.... Cut the barrel back or just hang a new tube on it

 

[Tgunz64]

If I have enough thickness to keep the barrel 20” long I think I’ll have them cut it and thread it. I’ll call them tomorrow and have the gunsmith take measurements and see where it ends up being .600

 

[Geno C.]

It’s doable

 

[Praeger]

Do what? Clamp on is a fucking joke! Crawl back into your hole!

Easy Spartacus . . . No fucking joke.

 

[Wannashootit]

Guess I'm the only one that's confused here.
Where is the .600 coming from? That's not enough OD for even a 1/2" tenon with a suitable shoulder.

 

[northern50]

Don’t use a shoulder. Square up the front of the barrel and align off that, and make a bushing to fit. . Similar to Geno’s solution.

 

[Tgunz64]

Guess I'm the only one that's confused here.
Where is the .600 coming from? That's not enough OD for even a 1/2" tenon with a suitable shoulder.

It’s comes from TBAC’s site and also Area 419’s site

 

[gnochi]

Per LRI, thread major diameter plus 0.100” is the bare minimum.

 

[Tgunz64]

Per LRI, thread major diameter plus 0.100” is the bare minimum.

LRI?

 

[1moaoff]

LRI?

Ouch!

 

[1moaoff]

Long Rifles Inc

 

[Tgunz64]

Here’s what I found for barrel threading

 

[gnochi]

Ah yeah, that writeup is for what the unthreaded tenon should measure to before threads are cut. I can’t even express how strongly I recommend against “threading without resizing barrel OD”.

 

[JGR1953]

It’s comes from TBAC’s site and also Area 419’s site

It comes from here....

Thunder Beast Arms Corporation [TBAC] | Tech | THREAD SPECIFICATIONS

 

[Tgunz64]

It comes from here....

Thunder Beast Arms Corporation [TBAC] | Tech | THREAD SPECIFICATIONS

yes it does and I emailed them about why the bold writing about why 1/2x28 is not sufficient for the 30 caliber. They said it has nothing to do with mounting a 30 cal can. It’s sufficient for it. It means Only shoot .223 Ammo through it. Nothing larger.
Here is my email to them:

ME:
Just wondering would I be able to mount an Ultra 9 on my Ruger Hawkeye 22-250 if I have at least a .600 shoulder and 1/2x28 threads? it wouldn’t be direct thread but either your CB mount or an Area 419 Hellfire mount. I’ve been hearing that you can’t mount the .30 cal cans using 1/2x28 thread mounts.

TBAC’s RESPONSE:
1/2x28 threads with a CB mount will work fine. It’s just that any of our 1/2” mounts only have 223 bores so you wouldn’t want to shoot a 30 cal through it. We do not recommend 1/2” threads for a 30 caliber round.

 

[Rthur]

R

 

[Wannashootit]

One of my real gripes is that there isn't fact-based, engineering data that provides true "industry standards" for exactly these questions.
Whether it's a torque shoulder for a brake or can, minimum barrel wall thickness when threading, and others...

I've always wanted .100 shoulder (.200 over major), but admit I've cheated on that when there was no other viable option.
50 seems awfully small to me- but then I gotta say, these guys surely engineered this interface/connection. They have to feel confident in its safety margins or they wouldn't do it.

I understand there are machining variables (heat, etc), steel alloy variables, etc.
But seems to me these are not particularly puzzling questions that can be physically and scientifically tested to establish "guidelines" for use by the industry as well as DIY'er machinists.

Poll 100 riflesmiths on these questions (and others) and you'll get 75 different answers (if not all 100).

Most of what we do is subject to personal preferences, as there are often several ways to skin whatever cat being dealt with and we all do what works best for us...but there should be a reference look-up for this type of stuff.

 

[gnochi]

Speaking as an engineer who’s had to develop simulation techniques from scratch for high pressure high temperature short term dynamic events, especially with abrasive particles in the mix, it’s generally poorly understood and the literature in industry is pretty pitiful. To really get a good understanding of what’s going on requires a PhD in jet turbine design, with a thesis on handling bird strike.

So, the body of research for this sort of stuff in gunsmithing is basically “what hasn’t blown up in that smith’s friend’s face” - regardless of what actually caused that failure.

TL;DR: the basic statics problem is trivial, the dynamics problem is a cast iron bitch, and industry is generally clueless outside specific focuses.