Threading light hunting rifles for a suppressor

[Gtscotty]

I recently bought a lightweight titanium can expressly for deer/elk hunting, and would like to start threading my main hunting rifles while my new suppressor is in NFA jail.

The problem I'm running into is that the light rifles I'd like to use don't have enough meat at the end of the barrels to form an adequate shoulder. The suggested minimum barrel diameter for a 9/16x24 thread is 0.662, and for the standard 5/8x24 is 0.725.

My two favorite hunting rifles are a Browning X-Bolt and a Tikka T3 SL. The Browning has a barrel diameter of 0.599" at the muzzle and 0.609" 1 inch back. The Tikka has a barrel diameter of 0.625" at the muzzle, and 0.635" 1 inch back. Obviously, neither of these barrels meet the minimum diameter for even 9/16x24" anywhere near the muzzle.

I'd prefer not to just thread smaller and slap an adapter on. The best option I've seen is in the following picture stolen from an old thread:



I believe that the gunsmith that did this just threaded further back than usual, turned and threaded a tapered nut to match and then permanently mounted it, providing a decent shoulder on a thin barrel.

Does anyone know a gunsmith who does this kind of thing? I've looked around and came up empty handed.

Are there other good options that would allow me to go at least 9/16" on the threading and still have a decent shoulder. Is anyone else running into similar problems? If so, any tips?

 

[adcoch1]

You could have a collar like the one in the picture machined and finished, then machine your barrel back the inch from the muzzle at threaded diam, then press on the collar and thread the stub sticking out. The collar part would be easy, but unless the barrel can be removed (which it can't easily from those two rifles), it's gotta go to a gunsmith with a lathe. Unless you have a friend with a lathe. It's not hard to do, but it can get iffy with legality in some locations. What i described above is how I'll add a suppressor to the tikka t3 im getting this summer...

 

[greyling22]

yeesh, that looks expensive. What if you just go 2 inches back? it would cut weight and bulk down.

or could you use a washer of some sort?

 

[Varminterror]

I'd weigh my options for reducing barrel length to find the necessary bore ceiling for threading. Producing a sufficient shoulder for the suppressor is one thing, but leaving a sufficiently thick bore ceiling to prevent flaring over time is another.

 

[MachIVshooter]

What are the calibers? 5/8-24 is recommended for .264-.338 caliber, but we have done 1/2-28 up to .300 Win mag. The minor diameter of 1/2-28 is .472", leaving .082" wall thickness on the minor. With your muzzle diameters, that would leave sufficient shoulder (.050" is our minimum for no waivers). >.100 wall thickness is preferable, but as these are hunting rifles, consider whether or not you'll ever warm them up to the point where a slightly thinner wall will be problematic.

If the calibers are >.30, you will have to either cut the barrel back or do a pressed/threaded on collar as in your picture. The latter is not a bad way to go, but more expensive and a little goofy looking.

You should definitely consider cutting back, though. Not only does it solve your shoulder issue, but helps offset the additional 7"-9" of suppressor you'll be attaching. A 24" or 26" tube plus a can is gonna snag every tree branch in the forest.

 

[Gtscotty]

You could have a collar like the one in the picture machined and finished, then machine your barrel back the inch from the muzzle at threaded diam, then press on the collar and thread the stub sticking out.

I'm not quite sure I'm following, are you suggesting having a collar press fit on, or threaded on? I was thinking it might be easier to have the barrel threaded back far enough to thread the collar on, to where it butts up against the small shoulder at the end of the threads, solder or epoxy in place, then perhaps machine the face flat for a good mating surface. I think that's what they did in the picture, I just don't know where to find someone that can do it... well. I'd be willing to pay probably $200 to have it done right. Otherwise I'm restricted to using a small number of rifles with flared barrel ends like the Barrett Lightweight, or a couple of the Rugers, settling for a heavier rifle, or having a custom profile barrel made for the rifles I like, priced at PacNor this is looking like a $700+ option.

Producing a sufficient shoulder for the suppressor is one thing, but leaving a sufficiently thick bore ceiling to prevent flaring over time is another.

That's exactly why I'm asking about other methods to use a larger diameter thread and still get sufficient shoulder on a thin barrel. I could have them all threaded 7/16x28 like my Kimber came from the factory, but I want more wall thickness. How much wall thickness is necessary to prevent muzzle expansion seems to be based more on opinion than studies or calculations. I would expect it to vary with chambering, load, barrel length and barrel material/heat treat.

What are the calibers?

The X-Bolt is a .30-06, and the Tikka is a .270.

The minor diameter of 1/2-28 is .472", leaving .082" wall thickness on the minor. With your muzzle diameters, that would leave sufficient shoulder (.050" is our minimum for no waivers). >.100 wall thickness is preferable, but as these are hunting rifles, consider whether or not you'll ever warm them up to the point where a slightly thinner wall will be problematic.

I'm seeing minor diameters and minimum wall thickness relative to a .308 groove of for external threads of:

1/2x28 UNEF ~ 0.4562"..... 0.0741"
9/16x24 UNEF ~ 0.5114"..... 0.1017"
5/8x24 UNEF ~ 0.5739"..... 0.1329"

Seems like I'd be cutting it kind of close on the .30-06 with 1/2x28.

Both rifles have 22" barrels, and shoot well, I'm not interested in cutting the .30-06 down more than an inch or two, and the .270 has fluting that starts ~ 1.6" from the muzzle.

It seems to me that it would be preferable to thread 9/16x24 and have a collar permanently fitted than to go smaller and risk eventual muzzle expansion on a rifle that shoots very well for me, and that I shoot fairly often. I'm open to other opinions though, hence the thread.

I'm in Cheyenne, I've talked to one gunsmith down in Fort Collins that wanted to just thread it and permanently put on an adapter. I guess I'd like a more permanent, fool proof solution for the long run. I don't really know of any actual gunsmiths in the area, that would be up to this kind of work.

What I'd love to approximate is something like what Barrett did with their new field craft rifles (from their website):


In my mind they did the threaded hunting barrel right.

 

[adcoch1]

I'm not quite sure I'm following, are you suggesting having a collar press fit on, or threaded on? I was thinking it might be easier to have the barrel threaded back far enough to thread the collar on, to where it butts up against the small shoulder at the end of the threads, solder or epoxy in place, then perhaps machine the face flat for a good mating surface. I think that's what they did in the picture, I just don't know where to find someone that can do it... well. I'd be willing to pay probably $200 to have it done right. Otherwise I'm restricted to using a small number of rifles with flared barrel ends like the Barrett Lightweight, or a couple of the Rugers, settling for a heavier rifle, or having a custom profile barrel made for the rifles I like, priced at PacNor this is looking like a $700+ option.

Basically you are adding a washer to the barrel step to increase it's diameter to shoulder the suppressor or brake up to, so weather its threaded or just pressed on with epoxy, it will be as good as part of the original barrel. It would be easy to do with a lathe, as part of the true up to the barrel end before threading. I would NOT go smaller than a 5/8 x24 on a 30 cal barrel. My savage 30-06 has a barrel end diam that is .624, and i won't step down to 9/16 threads, it just doesn't leave enough meat left. Maybe for a 300 blk I'd work, but not for full power rifle cartridges...

 

[FL-NC]

I just bought nice new rifles to go with the suppressors- a Ruger American predator in 308 , a Ranch in 300 B-O, and a mossberg MVP thunder ranch in 223.

 

[MachIVshooter]

I'm seeing minor diameters and minimum wall thickness relative to a .308 groove of for external threads of:

1/2x28 UNEF ~ 0.4562"..... 0.0741"
9/16x24 UNEF ~ 0.5114"..... 0.1017"
5/8x24 UNEF ~ 0.5739"..... 0.1329"

Seems like I'd be cutting it kind of close on the .30-06 with 1/2x28.

Go here:

http://www.amesweb.info/Screws/AsmeUnifiedInchScrewThread.aspx

and punch in 1/2-28 with 2A and 2B respectively. .472" is the minimum minor pitch diameter for external threads. A .456" minor assumes that your valleys have zero radius or flat at the tip (sharp corner), and also applies 1A specs, which don't exist for 1/2-28. Unified 2A minor minimum is .4610:

http://www.efunda.com/designstandards/screws/unified.cfm?start=64&finish=147

.4563" is a UNR standard, and I don't think anyone out there is roll forming threads on muzzles.

IOW, when you're checking thread specs, check your source first. Arfcom or somesuch where some clown posts the first number he sees or can make sense of without really understanding what he's looking at is not helpful.

I use Kennametal Top Notch inserts, which crown the threads and have a radius at the tip on the NTF3R28E cutter that I use for threading 1/2-28.

https://www.kennametal.com/en/produ...8/56148748/100003236.html?orderNumber=1799416

I undercut at .465" and get no thread scratching with 2A threads.

This was a recent cut, crown & thread on a Bartlein stainless match grade blank I built onto a Badger action. It was 5/8-24, but you can clearly see that the threads do not have sharp valleys that would result in a true minor diameter, but a radius at the root that gives the pitch minor diameter, which is the result of using the Top Notch pitch-specific inserts (NTC3R24E in this case):

 

[Gtscotty]

I was looking at the Liberty Suppressors (I bought their Sovereign can) and AAC thread specs, and the efunda site you posted, not anything on Arfcom or whatever.

http://libertycans.net/education/faqs/thread-specifications/

http://www.advanced-armament.com/assets/images/pdf/manuals/ThreadGuideREV_01-040513.PDF

I guess I'm a bit rusty on thread specs, and my books at work didn't have lists of UNEF thread specs in them. So I see that your minimum pitch diameter is .472, what is the actual minor diameter on your 1/2x28 threads? Wouldn't it need to be less than the minimum minor diameter for a 2B internal thread of 0.461" to avoid interference?

Also, how did your guidelines for acceptable wall thickness come about (e.g. 0.1 is a preferable minimum, 0.05 requires a waiver)? It seems like the residual pressure at the muzzle (different amongst cartridges and barrel lengths), and material specs would drive significant changes to the minimum acceptable wall thickness, assuming pressure is the constraining factor as opposed to something like bending stresses from a can during firing.

 

[Decoy80]

Short rifles have stolen my heart. The lighter recoil and ease of movement both please me.
I would cut them off enough to have plenty of wall thickness and thread away.
Then my last action before removing it from the lathe would be a nice recessed crown.
Anything more than 21 or 22" on a hunting rifle is just in the way and lighter recoil and ease of movement are paramount to quick target acquisition and a flinch caused by your subconscious mind is a waste of powder and bullet leaving no meat on the ground for me.
Just my hop on the subject

 

[MachIVshooter]

I was looking at the Liberty Suppressors (I bought their Sovereign can) and AAC thread specs, not anything on Arfcom or whatever.

http://libertycans.net/education/faqs/thread-specifications/

http://www.advanced-armament.com/assets/images/pdf/manuals/ThreadGuideREV_01-040513.PDF

I guess I'm a bit rusty on thread specs, and my books at work didn't have lists of UNEF thread specs in them. So I see that your minimum pitch diameter is .472, what is the actual minor diameter on your 1/2x28 threads? Wouldn't it need to be less than the minimum minor diameter for a 2B internal thread of 0.461" to avoid interference?

I would think they'd know. Perhaps trying to compensate for people who can't measure properly or are trying to thread with sloppy machines or poorly hand-ground tool bits? I dunno.

2B internal is .461"-.470". Every 1/2-28 accessory I've measured comes back in the middle to high end of that range, .465" to .468". They all clear my .463"-.465" undercuts.

You did catch me asleep at the wheel on .472" as the basic minor, though. I don't actually measure the minor on my externals; I do the undercut, and then bring the threads in until the gauge goes on snug but smooth. The reason .472" stuck in my head is that it's the ID I was boring to on my Ti brakes and comps, where I actually did measure minor diameter. The reason for that is that full thread with taps in Ti is how you break taps! So I was running at least .472 minor on those internals.

Nevertheless, .456" is still the theoretical root minor for a perfect 60° V notch. If you actually cut threads to that minor, things are gonna be really sloppy.

This is my 700 LVSF .17 Rem, measuring on the undercut:

Also, how did your guidelines for acceptable wall thickness come about (e.g. 0.1 is a preferable minimum, 0.05 requires a waiver)? It seems like the residual pressure at the muzzle (different amongst cartridges and barrel lengths), and material specs would drive significant changes to the minimum acceptable wall thickness, assuming pressure is the constraining factor as opposed to something like bending stresses from a can during firing.

.100" barrel wall at muzzle is a pretty commonly accepted standard.

I won't cut walls down to .050" on high powered rifles; I said that anything which won't have at least .050" shoulder requires a waiver stating that people understand insufficient shoulder may result in improper alignment & baffle strikes. We are willing to thread up to .30 caliber at 1/2-28, but advise people that it's getting pretty thin. For someone who sights in once or twice a year and maybe fires a handful of rounds at critters, it should be fine. For a rifle that will see hundreds of rounds down range at paper annually, I would expect problems to arise with full power .284" and .308" cal rounds.

We do thread .45-70 at 5/8-24, which leaves pretty thin walls, but even running hotter loads, that's not in the same league as .30-06 or .300 mag pressures.

My personal preference is actually to thread all my rifle barrels with enough stock 5/8-24. Not because I'm worried about flaring a .224" or .244" caliber tube, but because I don't have dedicated cans for each rifle, and I don't like changing out direct thread mounts. Aside from AR barrels that came threaded, only my .22 Hornet, .22 mag and various .22 LR are 1/2-28. All of those 1/2-28 AR tubes sport 5/8-24 adapters, too.

You really just have to decide for yourself what you wish to do. If you don't mind the cost and aesthetics, 9/16-24 with a collar is mechanically the superior choice for your barrel dimensions. Or a completely custom adapter extending beyond the muzzle that can get you to 5/8-24. That's how I deal with handgun barrels when people can't buy a threaded tube. My S&W 4516-1 I made a 5/8-24 adapter for that is internally threaded 9/16-40 to install on a cut 4506 barrel.

Likewise, my DB9FS has a custom 5/8-24 adapter that is internally threaded .470-32. If I were doing such an adapter on a bolt gun, of course, it would be permanently installed without wrench flats. Can't do that with short recoil semi auto pistols!

 

[MCMXI]

how did your guidelines for acceptable wall thickness come about (e.g. 0.1 is a preferable minimum, 0.05 requires a waiver)? It seems like the residual pressure at the muzzle (different amongst cartridges and barrel lengths), and material specs would drive significant changes to the minimum acceptable wall thickness, assuming pressure is the constraining factor as opposed to something like bending stresses from a can during firing.

We are willing to thread up to .30 caliber at 1/2-28, but advise people that it's getting pretty thin.

Even without a heavy suppressor attached, there are hoop stresses, axial stresses and radial stresses to consider, and then there's the fact that most will shoot the rifle with the threads somewhat supported by either a thread protector or muzzle brake. Now add in the complexity of a suppressor hanging off the threads and the potential for plenty of heat and it rapidly becomes a complicated problem.

I actually like the solution that was presented in the first post. That flared and matched adapter looks good.

 

[MachIVshooter]

Even without a heavy suppressor attached, there are hoop stresses, axial stresses and radial stresses to consider, and then there's the fact that most will shoot the rifle with the threads somewhat supported by either a thread protector or muzzle brake. Now add in the complexity of a suppressor hanging off the threads and the potential for plenty of heat and it rapidly becomes a complicated problem.

I actually like the solution that was presented in the first post. That flared and matched adapter looks good.

I'm not debating that it's less than ideal, but fact is there are .300 Win mag and .308 Win rifles out there with 1/2-28 muzzle threads shooting suppressed and zero reports of problems that I've found. There are even .308, .300 Winny and .300 RUM with 7/16-28 brakes.

Seamless 304 stainless tubing with .083" wall thickness and .500" OD has a working pressure rating of 6,700 PSI. Heat treated 410/416 SS or 4140 CRMO, the most common barrel steels, have much higher tensile strength than 300 series austenitic stainless grades (31 KSI yield for 304 vs. 85 KSI for tempered 416 SS and 129 KSI for 1,200° medium temper 4140). Pressures at the muzzle end of a rifle are going to vary, but a 22" or 24" tube .30 cal with a chamber pressure of ~60 KSI should be in the 8-10 KSI range for bore pressure by the time the bullet reaches the muzzle. Ergo, the math says there should not be a problem with .075-.080" barrel wall thickness if temperatures are kept moderate. And by moderate, I mean under 300°F, where you start to see a marked decrease in tensile and yield strength.

 

[MCMXI]

There are even .308, .300 Winny and .300 RUM with 7/16-24 brakes.

I'm not arguing with you about any of this, just making the point that there's a lot going on and the empirical data is important given all the possible permutations. Kimber Montana and Mountain Ascent rifles use 7/16"-28 threads up to .30 cal magnums without any issues and the muzzle O.D. is 0.56". I have read some articles claiming that the muzzle flares as the bullet leaves the barrel which can adversely affect accuracy/precision but I've yet to see that with any Kimber that I've shot. That said, I always have something on the muzzle either in the form of a thread protector or brake so shooting with the threads unsupported might be a different story. I'm kind of in a similar situation with a .450 BM AR rifle. I want to use an AAC Ti-RANT .45 can on it and need to have different threads cut but there isn't much barrel wall thickness. I would like to do something along the lines of what Gtscotty showed in his first post. I'll have to model something and find someone to make it for me.

My biggest concern with using a heavy suppressor on a sporter weight barrel with minimal barrel wall thickness would be fatigue failure of the threads, or more likely the undercut. I haven't seen any rigorous testing of suppressors on sporter weight barrels. Even though suppressors are less efficient with significant volume being behind the muzzle, I'm surprised that we don't see more offerings with suppressors that extend rearward. Not only do the help the balance of the rifle, they change the loading on the muzzle threads and reduce the overall length of the rifle.

 

[MachIVshooter]

I'm kind of in a similar situation with a .450 BM AR rifle. I want to use an AAC Ti-RANT .45 can on it and need to have different threads cut but there isn't much barrel wall thickness. I would like to do something along the lines of what Gtscotty showed in his first post. I'll have to model something and find someone to make it for me.

I would think that your .450 BM has at least .720-.730" barrel OD, Yes? That would leave enough shoulder with 5/8-24 threads. We have threaded .450 Marlin, .45-70 and .458 Socom at 5/8-24, no need for pressed or threaded sleeves. Haven't had a .450 BM through, but it's less potent than those cartridges.

 

[MCMXI]

I would think that your .450 BM has at least .720-.730" barrel OD, Yes? That would leave enough shoulder with 5/8-24 threads.

Yes, 0.740" O.D. and it's currently threaded 11/16"-24 from the factory. 5/8"-24 has a minor diameter (3A, external) of 0.5739" and the undercut according to TBA is 0.5750". AAC is now offering a 5/8"-24 fixed barrel adapter for the Ti-RANT 45 so this might be the way to go. You mentioned that you don't cut the threads to the minor diameter to avoid a loose fit so assuming the undercut dimension of 0.5750" that would leave a barrel wall thickness of about 0.062", but as I mentioned earlier, I wouldn't shoot the rifle with unsupported threads.

 

[MachIVshooter]

Yes, 0.740" O.D. and it's currently threaded 11/16"-24 from the factory. 5/8"-24 has a minor diameter (3A, external) of 0.5739" and the undercut according to TBA is 0.5750". AAC is now offering a 5/8"-24 fixed barrel adapter for the Ti-RANT 45 so this might be the way to go. You mentioned that you don't cut the threads to the minor diameter to avoid a loose fit so assuming the undercut dimension of 0.5750" that would leave a barrel wall thickness of about 0.062", but as I mentioned earlier, I wouldn't shoot the rifle with unsupported threads.

Yeah, if you're gonna use a semi-permanent adapter, I would have the threads cut to be a very tight fit. That's what I do on my pistol barrel adapters; they can be removed, but not easily. I almost always tap thread internals under .750, so when I cut the threads on the barrel, I take it a half thou at a time until I get to where it goes on, but there is significant effort to crank it all the way down. Then I red loctite them. It's not so much for support in this application as keeping the adapters from unscrewing when the can is removed, but same process.

This is the Diamondback DB9FS with my 5/8-24 adapter. Barrel OD is .520", and the threads are .470"-32. it seats on both the muzzle and the tiny shoulder behind the .470" threads. No wrench flats on this one; I cut an internal 3/8" hex

And this is what 5/8-24 ends up looking like on a thin .45 cal barrel. This is my Marlin Camp 45:

 

[Gtscotty]

My personal preference is actually to thread all my rifle barrels with enough stock 5/8-24.

That's actually what I'd like to do, the Sovereign will come with a 1/2x28 DT adapter, and a 5/8x24 DT adapter, plus the Saker 7.62 I already have wears a 5/8x24 adapter most of the time. I just don't think the two rifles I want to thread have enough diameter at any reasonable length to go with a straight 5/8x24 thread. I could also just buy rifles that already come so threaded, but I've gone through a bunch of rifles finding what I like, and I'd prefer a solution that would allow me to modify any future hunting rifles I pick up as well, with no consideration towards buying a heavier barrel. I thought about selling a few rifles and picking up one of those Barrett Lightweights, but I just don't think I can live with a safety that doesn't lock the bolt for backpack hunting.

My biggest concern with using a heavy suppressor on a sporter weight barrel with minimal barrel wall thickness would be fatigue failure of the threads, or more likely the undercut.

My thoughts exactly, I perused the thread fatigue section in Shigley's for a few minutes this morning before I had to get to work. I don't think I'm inclined to try and wade through the calculations, I'd rather just try to stick with the largest thread pattern I can get away with and have a collar and machined to produce a shoulder.

And this is what 5/8-24 ends up looking like on a thin .45 cal barrel. This is my Marlin Camp 45

How much shoulder is on that barrel? Any issues with your suppressor squaring up?

 

[Dentite]

I'm in the same boat. After much deliberation, reading, research, etc, I'm buying new rifles with threaded barrels.

I agree with you. I wish more manufacturers would make rifles with sporter weight barrels with a wider threaded portion at the muzzle.

 

[MCMXI]

And this is what 5/8-24 ends up looking like on a thin .45 cal barrel. This is my Marlin Camp 45:

What's the O.D. of that barrel?

 

[MachIVshooter]

What's the O.D. of that barrel?

.692" at the shoulder

Any issues with your suppressor squaring up?

Nope. I use a SiCo Hybrid on it, which has a .550" through bore anyway, but the rifle bore axis and suppressor bore axis are aligned well enough that bullets would clear a .480" aperture easily. I'd get a photo from the front, but they never turn out worth a pinch for me.

For the record, removing & reinstalling barrels on the Marlin Camp carbines is a PITA. Also, 230 gr. ball is supersonic from a 16" tube shooting here at 6,800 ft