Gunsmithing Thin barrel threading... possible?

[SABuzzard]

I'm looking for a way to get an AAC 51t flash hider/suppressor mount on a 30 caliber barrel with an OD of 0.575. Clearly it's too skinny for 5/8x24 threads. So, does it sound like a reasonable idea to thread it 1/2x28 and permanently install the flash hider/suppressor mount? The 1/2x28 flash hider may have to be bored out to accommodate the 30 caliber round but the 30 caliber can would fit the mount.

My other option is to sent the rifle back to the manufacturer and have a new barrel with a thicker pre-threaded collar on the muzzle installed. That would run me about $300.00 plus shipping.

It's a Sig Sauer 556R (7.62x39) w/ 16" barrel.

thoughts?

 

[SABuzzard]

Just realized there is a 9/16x24 option. May have solved my own problem.

 

[Aeon1]

Just realized there is a 9/16x24 option. May have solved my own problem.

Lets see if I got this right.

Muzzle = .575"
9/16" = .5625"
.575" - .5625" = .0125"
.0125"/2 = .00625"

So threading to 9/16" will leave you with an ~.006" shoulder for the brake to register against. Not even close to being enough unless you plan on the brake registering on the muzzle which is not typical but possible.

Another thought, If you were able to find a clamp on brake in 9/16" you'd be all set with no worries.

The 1/2" threaded brake would leave you with a barrel wall thickness of .096" and a .037" shoulder for the brake to register. A .050" shoulder would be more optimal in my opinion but I've known others to use a shoulder this small. I ran hoop stress calcs for 15Kpsi pressure at muzzle with a .308 bore and .500 muzzle dia and found the stress to be ~35Kpsi which is far under the yield strength for 416ss. Muzzle pressure is likely to be far below what I used in the calcs so my WAG is you would be fine.

 

[SABuzzard]

Lets see if I got this right.

Muzzle = .575"
9/16" = .5625"
.575" - .5625" = .0125"
.0125"/2 = .00625"

So threading to 9/16" will leave you with an ~.006" shoulder for the brake to register against. Not even close to being enough unless you plan on the brake registering on the muzzle which is not typical but possible.

Another thought, If you were able to find a clamp on brake in 9/16" you'd be all set with no worries.

The 1/2" threaded brake would leave you with a barrel wall thickness of .096" and a .037" shoulder for the brake to register. A .050" shoulder would be more optimal in my opinion but I've known others to use a shoulder this small. I ran hoop stress calcs for 15Kpsi pressure at muzzle with a .308 bore and .500 muzzle dia and found the stress to be ~35Kpsi which is far under the yield strength for 416ss. Muzzle pressure is likely to be far below what I used in the calcs so my WAG is you would be fine.

Aeon1 - thank you for calculating/working through that. Great info.

 

[SABuzzard]

Anybody have experience/thoughts on TIG welding or pinning this type of brake on a barrel. So say use the 9/16x24 that would leave almost no shoulder to index off of and weld/pin it in place. I'd like to leave as much metal on the barrel as possible.

Anybody have any experience running a 1/2x28 threaded muzzle on a .308 caliber rifle? This one is a 7.62x39.

 

[RADcustom]

The first 308 barrels from dpms were threaded 1/2x28 and had no issues.

 

[Travis S]

Can you cut the barrel back and have the brake permanently attached?

 

[jonaddis84]

I would go with the 1/2" threads and rockset the brake on. Just make sure the barrel is threaded competently and a good 3A fit and you should be fine. Youre better off having a decent shoulder to locate the brake than a thicker barrel.

 

[stangfish]

You can also but up to the muzzle with your break rather than the .006 lip you will have with a 9/16 thread.

 

[SABuzzard]

Can you cut the barrel back and have the brake permanently attached?

It's a pencil barrel. I wouldn't gain any diameter by moving it back. A local smith felt like there wasn't enough metal/thickness left in the barrel to pin and weld the QD/brake without risking it to warp or lose strength.

 

[SABuzzard]

You can also but up to the muzzle with your break rather than the .006 lip you will have with a 9/16 thread.

That's basically what a local smith was thinking as well. I'm giving him a little time to think through the 1/2x28 with shoulder or 9/16x24 indexed on the muzzle.

Unfortunately doesn't seem to be a clear consensus or plan of action here.

 

[Travis S]

I didn't realize it was a straight pencil. Sounds like a handy rifle you've got there.

 

[Guest]

The old way to do pencil barrels, was cut the largest thread the barrel diameter would 100% except to thread spec. Then taper outward behind the last thread an add a tapered shoulder stop that is heat differential set. The longer the taper the better. Then cut it square to the bore behind the last thread. A taper fit that is done correctly, and heat differential set, will require a puller or heat to remove.
I prefer setting the block first, squaring it, then threading but, it can be done in reverse as well.

 

[SABuzzard]

Thanks guys. All good info. Will help when discussing options with local smith.

 

[RetireVetUSAF]

I'm looking for a way to get an AAC 51t flash hider/suppressor mount on a 30 caliber barrel with an OD of 0.575. Clearly it's too skinny for 5/8x24 threads. So, does it sound like a reasonable idea to thread it 1/2x28 and permanently install the flash hider/suppressor mount? The 1/2x28 flash hider may have to be bored out to accommodate the 30 caliber round but the 30 caliber can would fit the mount.

My other option is to sent the rifle back to the manufacturer and have a new barrel with a thicker pre-threaded collar on the muzzle installed. That would run me about $300.00 plus shipping.

It's a Sig Sauer 556R (7.62x39) w/ 16" barrel.

thoughts?

Maybe this video from Gavintoobe will help. I sent the video to my gunsmith and he said he can do this to my Win Model 70 in 300 WSM. I also want to suppress it. video here:

 

[Yondering]

Maybe this video from Gavintoobe will help. I sent the video to my gunsmith and he said he can do this to my Win Model 70 in 300 WSM. I also want to suppress it. video here:

Gotta remember to read those thread timestamps, bud. Good info but you replied to a 10 year old conversation.

 

[FuhQ]

Maybe this video from Gavintoobe will help. I sent the video to my gunsmith and he said he can do this to my Win Model 70 in 300 WSM. I also want to suppress it. video here:

I was just talking to my smith a couple weeks ago about doing this to my 2 old 90’s Ruger M77 MKII rifles. They are a “big brother & little brother” set of stainless all-weather models with the old skeleton “boat paddle” synthetic stocks. One is a 24” 7mm RemMag (magnum sporter barrel), and the other is a 20” 7mm-08 Rem Mountain Rifle (full-size LOP, pencil barrel).

The Mountain Rifle 7mm-08 is so rare, I couldn’t even find any info about them on Google. I’d really hate to destroy the value since they are becoming increasingly rare, and I’ve had them forever (since new), but I also do not shoot unsuppressed rifles anymore…Even for just 1 shot while hunting. And it’s kind of pointless to have guns you don’t shoot. You pay enough and wait long enough for the cans, you might as well use them on everything you can. So, I’m going to get him to thread both of them and do this to create the new permanent shoulder for the can to seat against.

While he’s got them, he’s also drilling and tapping both receivers with 8-40 holes for EGW picatinny rails, so I won’t have to use those shitty proprietary Ruger rings anymore.

 

[LRI]

Maybe this will help:

GUNSMITHING SERVICES: Muzzle Threading AND Crowning service

The incredible surge in the popularity of suppressors makes a threaded muzzle almost standard equipment on today's precision rifle. LRI is well-equipped for this extremely popular upgrade. With our resources and experience, your device will attach trouble-free every time. Muzzle threads for...

www.longriflesinc.com

 

[RetireVetUSAF]

Gotta remember to read those thread timestamps, bud. Good info but you replied to a 10 year old conversation.

Ahhhh what a tangled web I weaved thanks and yeah I don't even know how the year didn't register. I clearly looked at it. I think I bumped my head once, thrice, too many times in the military!

 

[RetireVetUSAF]

I was just talking to my smith a couple weeks ago about doing this to my 2 old 90’s Ruger M77 MKII rifles. They are a “big brother & little brother” set of stainless all-weather models with the old skeleton “boat paddle” synthetic stocks. One is a 24” 7mm RemMag (magnum sporter barrel), and the other is a 20” 7mm-08 Rem Mountain Rifle (full-size LOP, pencil barrel).

The Mountain Rifle 7mm-08 is so rare, I couldn’t even find any info about them on Google. I’d really hate to destroy the value since they are becoming increasingly rare, and I’ve had them forever (since new), but I also do not shoot unsuppressed rifles anymore…Even for just 1 shot while hunting. And it’s kind of pointless to have guns you don’t shoot. You pay enough and wait long enough for the cans, you might as well use them on everything you can. So, I’m going to get him to thread both of them and do this to create the new permanent shoulder for the can to seat against.

While he’s got them, he’s also drilling and tapping both receivers with 8-40 holes for EGW picatinny rails, so I won’t have to use those shitty proprietary Ruger rings anymore.

That's awesome. I can see that being a tough call based on their age and rarity, but it seems like you made a choice that you'll be happy with and that's what really matters. My model 70 is actually nothing to brag about. When I bought it I didn't know that it was a big box store exclusive (maybe Cabela's .. not sure) but it came with a blind magazine, cheap stock, etc. Finding a stock was a challenge for a while until I ordered a Boyd's stock. It's chambered in 300 WSM and I know I can buy another (much better) 300 WSM for a reasonable price, but I've gotten so attached to this little rifle. I'm going to go ahead get it suppressor ready even though nearly everyone keeps telling me to buy a new one.

 

[Yondering]

Ahhhh what a tangled web I weaved thanks and yeah I don't even know how the year didn't register. I clearly looked at it. I think I bumped my head once, thrice, too many times in the military!

It happens to the best of us!