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Gunsmithing 1/2-28 on a 7mm .284" ?

Rprecision

Rprecision

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Nov 9, 2011
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Progressive Hell, CO
I had a barrel dealer recommend a 1/2"-28 muzzle thread for a sporter weight 7mm barrel.

By my calculations that would leave a thin profile from bore to root of the thread at .109" seems a bit thin for my comfort level. Anybody have any guidance on this? I think it should be a 5/8" 24.

Thanks
 
I have 5/8"-24 on my 280AI. I think that is usually the standard for like 6mm and up. Only seen 1/2"-28 when I look at building a vudoo 22lr barreled action. I'm no expert though.
 
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Rprecision said:
.607
Click to expand...
That would be why it was recommend you thread it 1/2-28 and not 5/8-24. Your muzzle is a little too thin to be threaded 5/8-24 while comfortable having a shoulder. You'd likely need to be at .650" at a minimum. Most like to see at least .725". That would give you a larger wall thickness, but not a great shoulder.
 
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You get into a thin enough barrel and 1/2x28 or 1/2x32 are the only options. I have threaded many .30 caliber barrels 1/2x28. I don't like doing it, but you have no option if your barrel is only .600 or smaller at the muzzle. If you do 9/16x24 you will have such a small shoulder that you can actually deform the shoulder without much torque on the muzzle device or suppressor.

I recommend doing the threads with no thread relief if the muzzle device can accommodate that. This keeps more material at the base of the threads where they are more likely to fail. I have threaded a .300 RUM 1/2x32 and many .30-06's 1/2-28 and have not had one fail.

In the OP's case I'd probably want to do a 9/16x24 and get an adapter to 5/8-24 from precision armament. I'd rockset the adapter on with just enough torque to not deform the shoulder.
 
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I'm fine with .050 shoulder for brakes. I rely on the shoulder to align- without a ton of torque. Light torque to align the shoulders- Rocksett to lock it in place in lieu of torque. I've done many dozens of 9/16" brakes on .30 cal skinny barrels, never had an issue.

Minimum .100 for suppressors. They're different animals, and I treat them differently.
 
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Assuming enough meat on the barrel, say .75" diameter or larger, what is the biggest caliber you'd feel safe with going 1/2x28? 6mm, 25, 6.5mm, 277...etc?

I almost picked up a Fierce Fury in 7mm Mag for a mountain Elk hunt, but they are threaded 1/2x28 and my Ultra 5 wouldn't work. Cutting and re-threading would have taken me too close to the fluting.
 
I'm going through this mental debate right now with my lightweight 7mmRM custom Browning A-Bolt II. It's got a 26" magnum sporter contour barrel on it, and I believe it's somewhere around .670" at the muzzle. It shoots amazing, but I want to thread it, and don't know if there's enough meat to put 5/8x24 threads on it. I plan on putting a Dead Air KeyMo brake on it, so there will be thread support 24/7, but I don't know if there will be enough shoulder to torque it properly. I'll have to measure the barrel next time I go to the safe for an exact diameter. I'm debating on 1/2x28 with the DA KeyMount brake, or cutting it back to 20"-22" to have enough meat on it for 5/8x24...But then you're losing a good bit of velocity. So, I'm at a loss for which way to go on it.
 
Mordamer said:
You get into a thin enough barrel and 1/2x28 or 1/2x32 are the only options. I have threaded many .30 caliber barrels 1/2x28. I don't like doing it, but you have no option if your barrel is only .600 or smaller at the muzzle. If you do 9/16x24 you will have such a small shoulder that you can actually deform the shoulder without much torque on the muzzle device or suppressor.

I recommend doing the threads with no thread relief if the muzzle device can accommodate that. This keeps more material at the base of the threads where they are more likely to fail. I have threaded a .300 RUM 1/2x32 and many .30-06's 1/2-28 and have not had one fail.

In the OP's case I'd probably want to do a 9/16x24 and get an adapter to 5/8-24 from precision armament. I'd rockset the adapter on with just enough torque to not deform the shoulder.
Click to expand...
Ever put a gauge pin at the muzzle of one of those 1/2x28 30 cal barrels?

Muzzle Threading — Don’t Remove Too Much Steel « 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. The reason is that the end of the barrel can bell out slightly, like a trombone, because too much steel...
bulletin.accurateshooter.com bulletin.accurateshooter.com
 
srt-4_uk said:
Ever put a gauge pin at the muzzle of one of those 1/2x28 30 cal barrels?

Muzzle Threading — Don’t Remove Too Much Steel « 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. The reason is that the end of the barrel can bell out slightly, like a trombone, because too much steel...
bulletin.accurateshooter.com bulletin.accurateshooter.com
Click to expand...
Nope. And they still shoot the same after as they did before.
 
FuhQ said:
I'm going through this mental debate right now with my lightweight 7mmRM custom Browning A-Bolt II. It's got a 26" magnum sporter contour barrel on it, and I believe it's somewhere around .670" at the muzzle. It shoots amazing, but I want to thread it, and don't know if there's enough meat to put 5/8x24 threads on it. I plan on putting a Dead Air KeyMo brake on it, so there will be thread support 24/7, but I don't know if there will be enough shoulder to torque it properly. I'll have to measure the barrel next time I go to the safe for an exact diameter. I'm debating on 1/2x28 with the DA KeyMount brake, or cutting it back to 20"-22" to have enough meat on it for 5/8x24...But then you're losing a good bit of velocity. So, I'm at a loss for which way to go on it.
Click to expand...

If it is .670 then 9/16x24 is your best option. Dead air makes a brake in this thread pitch if I remember correctly.
 
WB300 said:
Assuming enough meat on the barrel, say .75" diameter or larger, what is the biggest caliber you'd feel safe with going 1/2x28? 6mm, 25, 6.5mm, 277...etc?
Click to expand...

Anyone???
 
Regardless of the first part of the question, we don't recommend 1/2 for anything larger than .223 for suppressor mounting.

Even if it'll take the pull force, imagine an off-angle drop on the tip of the suppressor and the force transmitted through that thin metal in some of the caliber vs. thread combinations.
 
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Mordamer said:
If you had plenty of meat on the barrel why would you thread as small as possible? You should be threading as large as possible.
Click to expand...

I understand. Just gaining knowledge.... Pros, Cons, and Why's.
 
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