Brake installation question.

[Varmint Hunter]

I've got a 30 Nosler rifle with, I believe, a #4 bbl. It measures .670" at the muzzle.
I've got a PK brake that I took off of a heavier bbl that was in 300RUM. The brake measures .520" when measuring the inside thread diameter.

Can the 30 Nosler barrel be threaded for my PK brake?

 

[FEENIX]

I've got a 30 Nosler rifle with, I believe, a #4 bbl. It measures .670" at the muzzle.
I've got a PK brake that I took off of a heavier bbl that was in 300RUM. The brake measures .520" when measuring the inside thread diameter.

Can the 30 Nosler barrel be threaded for my PK brake?

That depends on the PK thread, I.e., 5/8-32. You might want to get with your gunsmith as they have a min barrel OD at the muzzle safety requirement for a particular thread and caliber/chambering.

 

[IdahoCTD]

.520 on the minor diameter means 9/16" threads and most likely 9/16x24. That is what I would run on a .670" muzzle diameter .

 

[Varmint Hunter]

Thanks for the input guys.

Update - I contacted my smith and he believes that it is doable based on the measurements that I provided.

 

[Boe]

9/16 tenon, That's not going to leave you enough barrel wall thickness. .1060 on a Button rifled barrel? 5/8 tenon will give you .1585 But that doesn't leave much of a shoulder for the brake .0225 . I would look for a face mounted brake.
Richard Hilts
Hilts Accuracy Custom Rifles

 

[FEENIX]

Thanks for the input guys.

Update - I contacted my smith and he believes that it is doable based on the measurements that I provided.

I just checked Kirby's site, and he threads his small 3-port PK with 9/16-28 for barrels with OD of .585-.750, so I guess you might be good to go.

 

[tobnpr]

^^
9/16" tenon, not 5/8"
.560 +/- OD, fine for a brake with a muzzle OD of .670.

 

[Boe]

If you guys check the bores with Deltronic pins before and after you machine the tenon you're going to see the bore expanded a few tenths after you machine the tenon on some thin walled barrels. Premium Barrel manufacturers go to great lengths to keep the bore a consistent diameter. There's a reason for that. There's more ways to do a job wrong than it is to do it right.

Richard Hilts

 

[FEENIX]

That depends on the PK thread, I.e., 5/8-32. You might want to get with your gunsmith as they have a min barrel OD at the muzzle safety requirement for a particular thread and caliber/chambering.

Yikes! 5/8-24.

 

[Len Backus]

If you guys check the bores with Deltronic pins before and after you machine the tenon you're going to see the bore expanded a few tenths after you machine the tenon on some thin walled barrels. Premium Barrel manufacturers go to great lengths to keep the bore a consistent diameter. There's a reason for that. There's more ways to do a job wrong than it is to do it right.

Richard Hilts
Hilts Accuracy Custom Rifles

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Hilts Accuracy Custom Rifles

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www.longrangehunting.com

 

[Varmint Hunter]

I just checked Kirby's site, and he threads his small 3-port PK with 9/16-28 for barrels with OD of .585-.750, so I guess you might be good to go.

Based on the dimensions I provided my smith, which are admittedly crude, he believes that there will be .054" per side of shoulder. I guess that he will know better when I get there.

If the brake won't safely fit, I'm interested in one of the newer, Salmon River titanium "tiny" brakes. Aesthetically, it would be a lot nicer, but I already have the PK brake and they are effective brakes.

 

[FEENIX]

Based on the dimensions I provided my smith, which are admittedly crude, he believes that there will be .054" per side of shoulder. I guess that he will know better when I get there.

If the brake won't safely fit, I'm interested in one of the newer, Salmon River titanium "tiny" brakes. Aesthetically, it would be a lot nicer, but I already have the PK brake and they are effective brakes.

I think you should be fine. If Kirby (@Fiftydriver ) runs them .585-.750" OD on .224-.375 calibers with 65-110 grains of powder, I think you're OK. Kirby knows his stuff and does extensive tests on his products. Nathan does too! Good luck!

 

[tobnpr]

There's two primary considerations.
Barrel wall thickness which Boe mentioned. This is what's "left" of the barrel beyond the thread minor diameter to the bore.
It's not enough to just consider the major diameter of the thread tenon and barrel OD for the mating shoulder. Big difference in wall thickness between a 6mm and 30 cal bore and any given pitch diameter.

There's no hard and fast rule, every smith has their own comfort level. "Bell mouth" can indeed happen.
You'll find at least a handful of manufacturers that thread skinny muzzle hunting barrels in .300 WM in 1/2"-28.
I've done that, but reluctantly. How the threads are cut, and the correct root threadform is critical to minimize this happening.

With 9/16"-24 there's just over .100 barrel wall thickness with a .308 groove diameter which I'm perfectly fine with. Others may feel differently.

Even in circumstances where there's inadequate barrels shoulder, it's simple enough to use (or modify) a brake that indexes off the muzzle instead of a torque shoulder.

 

[bamban]

If you guys check the bores with Deltronic pins before and after you machine the tenon you're going to see the bore expanded a few tenths after you machine the tenon on some thin walled barrels. Premium Barrel manufacturers go to great lengths to keep the bore a consistent diameter. There's a reason for that. There's more ways to do a job wrong than it is to do it right.

Richard Hilts

Here's Robert Whiteley's work done on the subject

Barrel End Threading — Bigger Diameter is Better « Daily Bulletin

Our friend Robert Whitley of ARX Enterprises LLC has learned, through careful measurement and testing, that some barrels threaded 5/8 x 24 TPI at the muzzle may not deliver optimal accuracy.

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