Pattern In Bore - What Is It?

[Brians356]

Brian the button irons in the reamer marks !

Translate "irons in" please. Meaning it should iron them away, or it follows the marks, and transfers the same pattern to the grooves? Or something else?
-

 

[Brians356]

The only way to tell is with a slug . But in all likely hood it's larger where the both lands and grooves exhibit reamer marks . Sometimes a tight patch on a rod will tell you . A lead slug is the best way .
Gary

I believe a tight patch loosens up in the middle, then tightens up again before the muzzle. I can index the outside of the barrel using the borescope for reference, then try to correlate patch tightness with the index marks. I suppose if it tightens up a bit approaching the muzzle, and the lands smooth out again, that's a good thing for accuracy. (I know good Walther air rifle barrels are choked slightly the last few inches behind the muzzle, but they shoot pure lead pellets.)
-

 

[bigngreen]

Every barrel guy I've talked to called that button chatter from either a hard spot or poor lube.

 

[Ggmac]

It impresses the reamer marks

 

[Brians356]

I have a Blackstar stainless barrel from the 1990s which had that electro-polished bore they tried to exploit. Using the technology they claimed they made the bore taper slightly tighter from chamber to muzzle. I noticed that the last inch or so inside the muzzle showed very faint chatter marks like the ones seen here. You could see them, but not feel them. I had my gunsmith chop an inch off the barrel, probably was not necessary as it shot the same before and after - excellently (still does). Anyway, if the bore does taper towards the muzzle, it would make sense that the marks only started to show up (were not cleaned up by the electro-polishing) at the very end of the taper.

Incidentally, that Blackstar barrel has only ever had moly-coated bullets through it - never a single bare copper jacket. When I got my Lyman Borecam and looked inside it for the first time, I was astounded by how clean and smooth it is. And the throat is not fire-cracked. I don't own any other custom barrels, so I don't know what those top tier bores looks like, but this Blackstar is unlike any normal factory barrel I've looked inside - there are virtually no artifacts to observe.
-

 

[Ggmac]

A few too many variables to guess at that . If the barrel was tapered and not properly stress relieved . If the bore was tighter at the muzzle ,all marks should have been the same , I'm not sure of the polishing method they used .

I'll try to find some good articles on barrel button Manufact . It'll be from my library and may take a few days , if your interested .
Gary

 

[Brians356]

If the bore was tighter at the muzzle ,all marks should have been the same , I'm not sure of the polishing method they used .

They put an electrode in the bore with an air gap, then used an electrolytic process to etch material away in a controlled fashion. In order to make the bore tighter towards the muzzle, they applied less current there, or withdrew the rod, or whatever. Since it was not a mechanical abrasive process, it did not "follow" the existing bore profile. Given that, toolmarks could have been left intact in the region where less etching was applied.
-

 

[Ggmac]

Black star barrels are button rifled ? Cut ? Hammer forged ?

 

[Brians356]

They haven't been made for decades, cant find old article(s) I used to reference. (I have hard copy at home somewhere). But I think their blanks were Lothar Walthers, so that should tell you. Also, they were an extra hard stainless alloy, I seem to recall "SS700". But maybe L-50.
-

 

[savagedasher]

If they were hammer forged that could be why the marks look indexed. Larry

 

[savagedasher]

They haven't been made for decades, cant find old article(s) I used to reference. (I have hard copy at home somewhere). But I think their blanks were Lothar Walthers, so that should tell you. Also, they were an extra hard stainless alloy, I seem to recall "700". But maybe L-50.
-

I can't remember seeing a stainless barrel in the 70 .
Is the barrel blue ? Larry

 

[Brians356]

Guys, we are mixing barrels here. This thread is about Ruger M77 from 1970s, blued chromoly barrel OEM.

I also mentioned Blackstar (off topic) which is stainless, Walther blank.
-

 

[Brians356]

I don't see how a hammer forged barrel could have these apparent chatter marks. And I have no idea how Ruger made their barrels in the 1970s.
-

 

[savagedasher]

I don't see how a hammer forged barrel could have these apparent chatter marks. And I have no idea how Ruger made their barrels in the 1970s.
-

I never see a reamer chatter like it normally is being turned. But what do I know. Larry

 

[Brians356]

I never see a reamer chatter like it normally is being turned. But what do I know. Larry

I meant button chatter. But something caused those perfectly regular steps.
-

 

[savagedasher]

I meant button chatter. But something caused those perfectly regular steps.
-

That's about the amount a the mandrill is moved when hammer forging is done . The button raise for the rifling.
Like I said what do I know Larry

 

[Ggmac]

Ruger barrels were buttoned in the 70-early 80 s maybe later . Thr marks you see are from the reamer progressing thru the drilled hole .
Your correct Larry as always , have another guess at it .

 

[savagedasher]

Ruger barrels were buttoned in the 70-early 80 s maybe later . Thr marks you see are from the reamer progressing thru the drilled hole .
Your correct Larry as always , have another guess at it .

I think all Ruger barrels were hammered forged And still are. Larry

 

[stansrifles]

Common on OEM barrels. Reamer marks in button barrel. Will have more effect on copper and carbon fouling. It shows the barrel was not pre lapped before buttoning. This is further demonstrated by there obviously are tight and or loose spots in the barrel. Live with it and find out if your gun likes shooting clean or fouled better. If you rebarrel get a premium grade barrel that has been properly, stress relieved multiple times, drilled straight, reamed, prepped, then buttoned or cut, then post stress relieved and post lapped. The barrel should have some choke in it.
Nat Lambeth

What is the choke for..

 

[msinc]

How could there be marks in the grooves, then, since the grooves didn't exist until after the rifling was completed? Only the button or broach could have marked the bottoms of the grooves. In my mind, it almost has to be chattering.
-

This is an excellent question and we have to look at the different methods of rifling to understand...first of all, when a rifled barrel is made there are some common steps that have to take place before the rifling is created. The different methods of creating or putting the rifling into a bore is where I think it gets confusing.
So, if we are going to make a barrel we'll start off with a rod of steel. It gets deep hole drilled and the result is that bar of steel no longer solid, it now has a hole running the entire length. This hole will eventually become the finished bore, but it is undersized. Next we need to smooth out this rough bore and put it on size according to how it will be rifled. In the case of a button rifled barrel it needs to be as smooth as we can get it and be slightly undersized from the finished bore diameter. There is some spring back in the steel and this dictates the size needed. To get it smooth and on size it is reamed with a chucking reamer. This is a straight flute high precision reamer that follows the existing deep hole drilled bore and doesn't take out much. Many things affect the finish of the reamed bore...rpm {speed it was turned when reamed}, feed speed {speed the reamer was advanced}, etc. The coolant/lubricant being used. The object is to get as smooth as possible the finished hole so we can now do the rifling.
In the case of button rifling, the button is basically a carbide bullet on the end of a rod that is pulled thru the bore. It is larger in diameter than the bore and is like a snake swallowing an egg. This will swage or "iron" the rifling into the surface of the bore. Any tool marks left from either the deep hole drill or the chucking reamer will be smoothed over in this process somewhat and may or, if they are "large" or severe enough, may not be swaged out. If they are bad enough then you will see the "ironed in" tool marks, and they will appear on both the lands and grooves.
In the case of broached rifling which I always thought was done in shorter pistol barrels the tool marks could be completely cut out. With single point cut rifling the lands must be on finished size because you are only cutting in the grooves, so you might see some reamer marks or now they use hones too, so you could see a very fine crosshatch pattern {Kimber is one that uses a barrel hone.} You might see the tooling or honing marks on the land surface but you wont see it in the groove because it was cut away.
Again, I was under the impression that Ruger hammer forged their barrels, so it makes sense that you would see the tooling marks on both the lands and grooves {assuming they were there to start with}. It would depend on how much "hammering" took place during this process. I doubt that sliding the mandrel out of the bore would do much to smooth out any resulting marks hammered in.
I hope this explains why you might see some tool marks in the finished bore of button rifled barrels. Custom barrel makers do their best to not have any tool marks, but they also finish the bore very slightly smaller to allow for lapping any marks out. The end goal is to have a bore that is dead straight, dead on size and zero tooling marks. Born out of necessity during WWII, button rifling is the fastest way to get there.