I have a Bushmaster Dissipator that I want to put on a diet. I want to have the barrel turned down and threaded for a flash suppressor.

Will the process of turning the barrel down and threading the end affect the muzzel crown? The barrel is chrome lined, and the crown is recessed and in good shape. I don't want to recrown the barrel, due to the chrome lining.

How do you chuck it up into a lathe (or whatever they do) without marring the crown?

You can chuck it up either in the headstock, on a steady rest or use a muzzle adapter, made of a softer material, to preserve your muzzle.

Due to space and other issues, I opted for the third:

You cannot properly cut threads without installing the barrel in both the headstock (breech) and the muzzle end in the tailstock. First you cut threads and fit the suppressor. Then you remove the barrel from the lathe, reinstall it in the headstock only and indicate it in. Then you recut the crown. Charles a Gunsmith.

If you can build/buy a steady rest for your lathe, that would be ideal.  Nothing touches the crown.

Thanks for the information.

I will have to talk to the smith I am thinking of hiring to do the work. It sounds like there is a way to do it without messing with the crown. At least now I will be able to discuss it in terms he understands.

I know chrome lined barrels get chopped all the time, but I don't want to disturb the chrome.

You cannot cut good accurate threads with a steady rest. A Gunsmith.

Quoted: You cannot cut good accurate threads with a steady rest. A Gunsmith.

Because the rest lacks rigidity?  That is how I cut 1/2 x 28(?) threads on a barrel I am working on, and I am pleased with the results.  Works OK for profiling barrels too.

Anyways, we are talking about fine pitch muzzle threads and not 10 pitch Springfeild or Mauser threads.

For cutting threads on a utility rifle, anything is fine as long as you are within a couple thou.  For anything presision, either in bullet placement of mechanical fit, it is a good practice to zero both at the muzzle and breech to make sure everything is concentric.  Personally, I don't thread precision barrels.  They're either not threaded or come that way from the company/'smith who knows what they are doing.

Precisely because the rest lacks rigidity. When you set the cutting tool, high speed or carbide, to make a cut the tool will push the barrel in the steady rest away from the tool at different rates on each side. You will undoubtedly get threads that are deeper on one side than on the other. This will probably show up as 'loose' threads in that the suppressor when threaded on will wobble from side to side. To minimize this you set the muzzle end in the tail stock and cut as needed. Threads are more uniform and lateral slop is eliminated. Mauser threads are 1.100 diameter 12 TPI, 60 degree angle, with a nominal depth ranging from 0.036 to 0.042 inches. Springfield, M1 and M14 threads are 10 TPI, square cut 90 degree, width of 0.050 inches and depth exactly of 0.020 inches. AR 15 suppressor threads are 1/2x28 TPI. I thread and contour lots of barrels from raw blanks every year. A Gunsmith.

So, I could have the barrel profile thinned down without affecting the crown, but to thread it nicely the muzzle needs to be reprofiled as well.

Maybe this smith I am going to use has or can make a brass muzzle adapter like mongo's.

Quoted: So, I could have the barrel profile thinned down without affecting the crown, but to thread it nicely the muzzle needs to be reprofiled as well. Maybe this smith I am going to use has or can make a brass muzzle adapter like mongo's.

I have a live center with interchangable tips on it.  If your 'smith doesn't have that style, the adapter won't work.  He may be able to make something that could work with his equipment, though.  My adapter allows me to cut threads on a barel using a die.  My lathe doesn't have threading capability at this time, so I do with what I have.

Quoted: You cannot cut good accurate threads with a steady rest. A Gunsmith.

BS! And my rifle is proof...

Not quite. To thin the barrel profile is called 'contouring'. To contour and to have the exterior of the barrel be concentric with the bore, you MUST use the tailstock to control the 'springing' effect of the barrel pushing away from the tool holder. That will affect the crown. There is no piece of metal you can insert in the muzzle that will not affect the crown. If the insert is hard (asin steel) it will damage the existing crown. If the insert is soft (as in brass or plastic) it will allow the barrel to push or spring away from the tool holder. To recrown a barrel is really not a very difficult job. It is the finishing touch to a professionally done barrel job. A Gunsmith.

Quoted: Not quite. To thin the barrel profile is called 'contouring'. To contour and to have the exterior of the barrel be concentric with the bore, you MUST use the tailstock to control the 'springing' effect of the barrel pushing away from the tool holder. That will affect the crown. There is no piece of metal you can insert in the muzzle that will not affect the crown. If the insert is hard (asin steel) it will damage the existing crown. If the insert is soft (as in brass or plastic) it will allow the barrel to push or spring away from the tool holder. To recrown a barrel is really not a very difficult job. It is the finishing touch to a professionally done barrel job. A Gunsmith.

I must have read your first post wrong or you left something out that was the "jist of the just" as your reply is a big +1.

in either way.. "Yeah, what HE said"..

Wizard - thank you I am only trying to help AR-10 make an informed decision. I am not soliciting business. I already am backed up for the next 5 or 6 months. Charles.

Quoted: Wizard - thank you I am only trying to help AR-10 make an informed decision. I am not soliciting business. I already am backed up for the next 5 or 6 months. Charles.

You're welcome. It would appear that I have not had nearly enough caffiene tonight to muster up the necessary powers of observation.

5 to 6 months backlog seems to be the common going for Gunsmiths everywhere. High demand + fewer gunsmiths = 5 to 6 month backlog.

Thanks for the explanations.  I think most of us with machinetools are self taught.  We dont' have V thread micrometers or CMM tools which can help us find errors in technique like that.  

In this case, a little finishing cut would turn a too tight to thread to way too loose leaving us scratching our heads in puzzlement.  

Quoted: You cannot cut good accurate threads with a steady rest. A Gunsmith.

Perhaps you meant to say, YOU cannot cut good accurate threads with a steady rest.  

I can.  And do.

This horse has been beat far past dead, and frankly IMHO this isn't the forum for it.  Take it to a machinist forum if you want an argument.

What we're talking about threading here isn't that precise - and doesn't require anything near the level of precision you are suggesting.

These flash hiders, and even most suppressors in my estimation are all threaded with a tap, nobody is single pointing these things.  With that said, most of the people that are threading these barrels are doing it with a die.

Maybe they set up the die using some old barstock laying around so the fit is tight, maybe not.  Look at how sloppy the fit is on most production barrels.

When I thread one of these, some I single point, some I run a die on.  In both cases, the threads are fit to the individual piece(flashider), single point by how deep I cut the thread - and with a die by how I set the die up(using an old piece of barrel or roundstock, whatever).  

As far as how hard your jamming the live center into the muzzle....if you're taking a very fine cut on each threading pass .001-.0015 you're not going to hurt a thing...buy a loupe and look at the crown for yourself.  

You can do whatever you'd like in your shop, clearly, but telling everybody "it can't be done that way", isn't right - and is untrue.  

I think a more accurate statement would be "I can't make money in my shop doing it that way, cause it would take me too long).

About beating a dead horse, I appreciate hearing ways to eliminate error like this.  The machinist's boards are often too generalized, and the board stars are more into selling machinery or telling funny stories of time in the shop.  The smiths on the pistol forums play their cards close with few exceptions.

Anyone can cut metal to shape and size to profit, but I am in it for fun and self satisfaction.  I am trying to get that last thou out of my parts.

I for one pay attention to a guy Derrick Martin trusted with his reputation and livelihood while he was doing his Guard duty fixing trucks and air conditioners.

Then there's always the time-proven ball bearing/lapping compound trick to redress the crown.  And it's virtually goof-proof as well.  

Adco does high quality work, the kind you want done.  Prices are very reasonable, and parkerizing IS INCLUDED in the price.

Adco saved my POS DMPS barrel from being a tomato stake.

Quoted: I have a Bushmaster Dissipator that I want to put on a diet. I want to have the barrel turned down and threaded for a flash suppressor.

This is an offering I have dreamed about for years.  The light weight of a skinny contour 16" barrel with the full length sight radius of the "Dissapator" style setup.

After all, why do most people choose a 16" barrel?  I will guess that their reason mirrors my own in that I want to get the shortest and lightest weight barrel I can get.  If I want heavy, I've got a 20" HBAR for that.  But the downside to the 16" barrel is the decreased sight radius afforded by the CAR-style gas system.  So, the "Dissapator" option was offered by Bushmaster and copied by many.

But I think even the "Dissapator" style package can be improved upon with the addition of a full-length light contoured barrel option to reduce its weight.

IMO, of course.  And we all know the adage about opinions.  

BTW, might it not be cheaper in your case to simply buy a skinny contour 16" barrel and just pay to have the second FSB pressed onto it or adapted to fit it by whatever means necessary?

BTW, might it not be cheaper in your case to simply buy a skinny contour 16" barrel and just pay to have the second FSB pressed onto it?

Another idea is to use a LW 16" barrel, cut down the FSB to fit under a FF handguard, and then index/install a flip up front sight on the tube's front.

Quoted: I for one pay attention to a guy Derrick Martin trusted with his reputation and livelihood while he was doing his Guard duty fixing trucks and air conditioners.

Touche,

However, we aren't talking about building an across the course competition rifle here, we're talking about threading a HBAR that is going to be reprofiled to save weight.

Just the recontouring is going to affect the internal diameter of the bore, and turning and threading the muzzle is going to open that up too.  Not the best for accuracy, but this fellow didn't ask about that...

BFARRIN 1-
We each choose to work to the level of competence and professional skill with which we are capable. I don't use dies for threads, EVER. I single point them all. Charles.