Gunsmithing 5/8 x 24 thread - muzzle devices - need advice

[Pflyinguy]

Sorry for the long story but.......I need some advice, I bought a supressor and I'm waiting on the paperwork, I don't want to start a debate so I won't mention the brand, it is a direct thread .30 cal can. I took my rifle to the dealer to test fit the can. The can would thread on about halfway and stop. My buddy's can (different brand) did the same thing. I did not want to damage the threads on the can so I did not force it. I read the company's website info they advise the 5/8 x 24 threads need to be .625 in diameter (the total diameter of the tops of the threads. The threads on my rifle measure .627

I talked to the gunsmith who threaded my barrel, he was strongly recommended here on the hide. His advice was to use "never seez" and work the muzzle device back and forth until it fit. I certainly dont want to damage the can and or the threads on my rifle. The Ops inc brake he installed, 5/8 x 24 fits perfectly, but the yankee hill thread protector i bought, also 5/8 x 24 wont even thread on one turn. What do I do? Any gunsmiths out there please chime in. Would running a 5/8 x 24 die on my threads cut the tops down to size? My buddy said I could sand the tops down but that seems risky... any advise would be appreciated.

 

[wnroscoe]

Re: 5/8 x 24 thread - muzzle devices - need advice

By hand with 240 grit paper you could polish the therads down slightly but, thats not what dictates thread fit. Where in Texas are you?

 

[jonaddis84]

Re: 5/8 x 24 thread - muzzle devices - need advice

What are you measuring the .627" with? Micrometer or calipers?

If it is that, or even close, that will definitely give you a tolerance fit, but not necessarily that alone like Roscoe said. Class 3A threads minimum major dia is 0.617, I usually cut tenons to .620 so if the threads "grow" the diameter at all, you still have clearance. Also keeps from having a sharp thread crest. If the device being threaded on ends up being on the small side of its tolerance window you will get quite a tight fit.

If you want to go buy a die, it may or may not solve your problem. Id say it would probably be alright if it just had to take some material off the crests, but if any needs to be removed from the root you might end up doing some damage.

 

[Keith Johns]

Re: 5/8 x 24 thread - muzzle devices - need advice

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Pflyinguy</div><div class="ubbcode-body"> His advice was to use "never seez" and work the muzzle device back and forth until it fit. </div></div>

I wouldn't do that.

When you got .627" did you mic. it or use calipers?

 

[AJ_Goddard]

Re: 5/8 x 24 thread - muzzle devices - need advice

Your can, your buddies can, and your yankee hill thread protector won't thread on. You measure .627 at the major diameter. Sounds like 4 things saying your barrel threads are not to spec.

 

[Pflyinguy]

Re: 5/8 x 24 thread - muzzle devices - need advice

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wnroscoe</div><div class="ubbcode-body">By hand with 240 grit paper you could polish the therads down slightly but, thats not what dictates thread fit. Where in Texas are you? </div></div>

I'm in the Austin area. I used calipers to measure the dax diameter of the threads. I will try to take a detailed pic of the threads. standby one.

 

[frankythefly]

Re: 5/8 x 24 thread - muzzle devices - need advice

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Pflyinguy</div><div class="ubbcode-body">Sorry for the long story but.......I need some advice, I bought a supressor and I'm waiting on the paperwork, I don't want to start a debate so I won't mention the brand, it is a direct thread .30 cal can. I took my rifle to the dealer to test fit the can. The can would thread on about halfway and stop. My buddy's can (different brand) did the same thing. I did not want to damage the threads on the can so I did not force it. I read the company's website info they advise the 5/8 x 24 threads need to be .625 in diameter (the total diameter of the tops of the threads. The threads on my rifle measure .627

I talked to the gunsmith who threaded my barrel, he was strongly recommended here on the hide. His advice was to use "never seez" and work the muzzle device back and forth until it fit. I certainly dont want to damage the can and or the threads on my rifle. The Ops inc brake he installed, 5/8 x 24 fits perfectly, but the yankee hill thread protector i bought, also 5/8 x 24 wont even thread on one turn. What do I do? Any gunsmiths out there please chime in. Would running a 5/8 x 24 die on my threads cut the tops down to size? My buddy said I could sand the tops down but that seems risky... any advise would be appreciated.

</div></div>

That has happened to me and my friend a few times. What we found was that the smith was using 5/8 x 24 Class 1a?!? threads, and was using a thread gauge of the same. Most cans are 5/8 x 24 class 3a(Except Tac Ops Class3b). Before you start pouring whatever crap on it and man handling the can on it, I would first find out what threads are the can, and what thread class your smith used. I am willing to bet the smith didn't cut the Class 3a threads. Also find out if your smith uses a thread gauge that is 5/8 x 24 class 3a, because if he doesn't then he wont be able to help you.

 

[Pflyinguy]

Re: 5/8 x 24 thread - muzzle devices - need advice

You can hopefully see the threads, from left to right, closest to the muzzle and about half way down the threads are shiny. That's from trying to thread the can and a Vortex brake on. It only went half way before stopping and getting really tight. The threads were darker before I tried to thread on the other devices. So my question is, are the valleys cut too shallow and the crests too high or both?

 

[Killer Spade 13]

Re: 5/8 x 24 thread - muzzle devices - need advice

Mic your threaded with a "thread mic" and make sure it is consistent in thread pitch diameter.

 

[frankythefly]

Re: 5/8 x 24 thread - muzzle devices - need advice

The Ops Brake, Surefire, and AAC seem to use Class 3b threads which fit everything as our rifles where fitted with one of those. When the smith recut the threads to class 3a we found all of the brakes to have a lot more play than before.(Which I thought Class 3a was supposed to be tigher?)

This is from another thread and it is Class 3a

http://www.snipershide.com/forum/ubbthre...amp;Search=true

 

[bohem]

Re: 5/8 x 24 thread - muzzle devices - need advice

Just tell him "fix it"

A well recommended builder from here should be more than willing to make it work for you.

The "anti-seize" comment worries me though.

 

[gunnergirl81]

Re: 5/8 x 24 thread - muzzle devices - need advice

Is it just me or do the thread valleys on the barrel in question seem a bit shallow? They just dont seem very sharp. Also they seem a bit thin. Worn cutter?

When we cut muzzle threads we have several test devices that we thread on and make sure they all fit. Suppressor makers are often all over the spec on their threads (one 5/8-24 direct thread can from one maker may thread on with no wiggle, the next may wiggle enough to make you nervous). You have two choices: Wait until you have your can in hand and get the smith to thread your muzzle for a nice fit, or the smith should thread it to fit most quality devices smoothly. You seem to be in the position of neither.

Some folks will just run a die down the threads, but I would be VERY careful. You can screw up the threads and as we all know, a little bit, added to the possibility of stacked tolerances can lead to a LOT of expense and heartache with a baffle strike. Even if you get it started smoothly a die has to be held square or it will remove material unevenly.

Lapping the can to the barrel? Golden rule: Always fix the cheapest part. Is it cheaper to get the barrel cut/crowned/threaded again, or have the cap or body of your can replaced?

Why are we discussing this with you instead of you discussing it with whoever threaded your barrel? If they promised class (insert spec here) threads, they have an obligation to deliver.

 

[jonaddis84]

Re: 5/8 x 24 thread - muzzle devices - need advice

I would definitely say he was using a worn tool, it didnt appear to cut near enough material out of the root of the threads, and the crests are also very sharp. Seems like he just kept going too deep trying to get the root depth and it pushed the crests up.

Thats going to need to be chucked back up and repaired.

 

[2156SMK]

Re: 5/8 x 24 thread - muzzle devices - need advice

Get an extra yankee hill thread protector and some 240grit lapping compound.
Lap the existing threads with the thread protector until your other known-good muzzle devices will thread on nicely.
If you start lapping and find that you can only get 1-2 more threads on, then there's definetly a problem with the threads and the whole job should probably be re-done.

 

[cal50]

Re: 5/8 x 24 thread - muzzle devices - need advice

Major diameter or pitch diameter.

If the thread diameter is too large you could turn / remove some from the OD. If the pitch diameter is too big you have a few choices. A button die of the correct size to chase the threads. Set it back up in a lathe and pick up the threads and single point cut / clean up the threads or the use of a thread file (24 pitch).

Determine if the major diameter is too big or your pitch diameter is too big. If the diameter is within spec I would use the thread file for the first line of attack if only a couple thousandths need to come off.

 

[gunnergirl81]

Re: 5/8 x 24 thread - muzzle devices - need advice

I still stand by my last statement. You paid SOMEBODY ELSE to do the job and they represented they'd do the job right. They should make you whole on the deal. If you touch the work and attempt to fix it yourself the smith now has no obligation to warranty his work.

My $0.02. I'm out.

 

[Shireman]

Re: 5/8 x 24 thread - muzzle devices - need advice

Just because they are 5/8" X 24 doesnt mean that anything threaded 5/8" x 24 will fit them.
Your brake does, your can does not. THe smith cut the barrel threads to fit your brake, and it does. Most cans are threaded to the tightest tolerances there are, some muzzle brakes, it doesnt matter.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: cal50</div><div class="ubbcode-body">Major diameter or pitch diameter.</div></div>

This is what matters. Take it back to your smith once you have your can so that you can take it with you. All he will have to do is take a thousandth or two off, either the major or the pitch. He can more than likely do this without even removing the action. It's very simple if you have the right tool.

Do Not force, anti seize, sand, lap, etc. Once you start messing with threads, you'll only wish you hadnt.

I had this same issue with 2 different rifles, it's really not that big of deal, If they're square, which I'm assuming they are since you didnt mention any muzzle brakes flying off and going down range.

 

[wtopace]

Re: 5/8 x 24 thread - muzzle devices - need advice

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: frankythefly</div><div class="ubbcode-body">The Ops Brake, Surefire, and AAC seem to use Class 3b threads which fit everything as our rifles where fitted with one of those. When the smith recut the threads to class 3a we found all of the brakes to have a lot more play than before.(Which I thought Class 3a was supposed to be tigher?)
</div></div>

Just so others aren't confused because of this post. Class 3A and 3B threads are the same exact class of fit. 3A is the designation for Class 3 external threads and 3B are internal threads.

Do not ask your smith to thread your barrel 5/8-24 Class 3B. You probably won't like what you get back after he hits it with a boring bar and his internal threading bit. (99% joking here, but I guess it could happen)

 

[3me]

Re: 5/8 x 24 thread - muzzle devices - need advice

Not meaning to call names or make accusations here, but it looks to me like he did the threading with a die instead of a threading tool on a lathe. You can only get a die on so far before the front of the die makes contact with the flat shoulder of the barrel. Since the back parts of the threads never were completely cut, your suppressor goes on as far as there are finished threads and then stops.

Just a thought, and I hope this is not the case because it is incredibly stupid to cut threads on a barrel using a die.