Pattern In Bore - What Is It?

[Brians356]

I see a regular checking pattern in a 1970s Ruger M77 barrel (270 Win).

The photos are from a Lyman Borecam, taken approximately 10%, 40%, and 90% down the bore from the chamber. Notice how much worse it is at 40%, especially atop the lands, which are nearly smooth at either end of the bore.

What causes this? It's so regular it must be machining marks or button chatter or something, no?
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[ireload2]

It looks like tool marks from a poor reaming job.
A premium barrel will not have much of that to begin with and what it left will be lapped out.

How many rounds have been fired? I have several rifles that look like that and shoot ok but it took about 75 to 200 rounds to iron some of that out.
I generally clean a rifle every 5 rounds as I shoot groups if it looks like that or if it is fouling for any reason.

 

[Brians356]

ireload2,

This is the original 1970s factory barrel. I bought the gun fairly well used around 1980, but never bore scoped it. Lord only knows how many rounds have been through it, but I've probably put about 100 through it myself. I wasn't particularly easy to coax accuracy out of, but I could get about 3/4 MOA out to 200 yards with 140-gr BTs.

At this point I'm inclined to run Tubb fire lapping pills through it, something I've done to two other rifles. But I'm open to suggestions. I'm not keen on rebarreling it, really.
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[Ggmac]

Barrel was drilled , reamed , button rifled , chamber and threaded . Those are reamer marks . Normal ! If your getting that grouping ,I'd not touch it .

 

[hpshooter]

I second what Ggmac says.

The bore scope tells me how well I am cleaning and how the throat is wearing, the target tells me how well the barrel shoots. What you are seeing is very common in factory button rifled barrels.

Leave the Ruger original, 3/4MOA at 200, on what is most likely a nice old hunting rifle, will bring down a lot of meat for the freezer IMO.

 

[Rustystud]

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

 

[Brians356]

Thanks, guys. I am learning one thing, the bore scope exaggerates everything. Tiny artifacts you couldn't feel with a dental pick look like the Grand Canyon.

One question: Does the stretch showing the deepest marks indicate a more open (less tight) bore diameter? (I.e. the tighter areas have the marks worn off the lands.)
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[clowdis]

You cannot get reamer marks in the grooves of a barrel, only on the lands. That's the only place a reamer ever touches the bore. What you see in the grooves is probably chatter marks from passing the button through the bore. I'd think that 3/4 minute accuracy out of this barrel is pretty darn good. Don't think I'd touch it.

 

[Brians356]

When folks mention "reamer" I don't associate that term the barrel's bore. I thought the basic bore was drilled, not reamed. Or is there a smaller pilot bore drilled first, which is then enlarged to land diameter by reaming?
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[savagedasher]

I can't think of any barrel making process that would put marks like that. It looks like they are indexed . Larry

 

[Brians356]

I can't think of any barrel making process that would put marks like that. It looks like they are indexed.

Seems like a button chattering could do it.
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[clowdis]

When folks mention "reamer" I don't associate that term the barrel's bore. I thought the basic bore was drilled, not reamed. Or is there a smaller pilot bore drilled first, which is then enlarged to land diameter by reaming?
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The barrel is drilled and then reamed to the proper diameter. Then they push the button through it or cut the grooves with a "broach" type cutter. Sometimes the button is just pushed through the barrel and you get whatever twist is on the button. That's the easier way to do it. Others turn the barrel at the proper twist rate while pushing the button (which is attached to a rod) through, which I believe gives a more consistent finish and twist rate with less chatter.

 

[savagedasher]

Seems like a button chattering could do it.
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How a button would chatter that deep is beyond me. Larry

 

[Ggmac]

Button didn't do it ! Reamer after drilling .

 

[msinc]

It was my understanding that Ruger hammer forged their barrels...but this may not be correct. Either way, those marks are from reaming to the proper size prior to rifling, no matter how it is rifled. Barrels have to be on size and as smooth as possible before the rifling is done.
What we are really seeing here is two things...the way gun manufacturers were free to operate BEFORE every SOB and his brother had a borescope {unfortunately way too many manufacturers still do operate this way} and the reason there are several custom barrel makers in existence today.

 

[savagedasher]

Button didn't do it ! Reamer after drilling .

Why would a reamer stop and move.?
Larry

 

[Brians356]

Either way, those marks are from reaming to the proper size prior to rifling,

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.
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[Ggmac]

Clowdish the bore is drilled , reamed , chambered threaded or threaded and chambered . Not the CHAMBERING REAMER !
Brian the button irons in the reamer marks !

 

[Brians356]

Anyone have an answer for my question about tight vs loose sections of the bore? I my "40%" section looser than the rest, so toolmarks remain on the lands (and worn away elsewhere)?
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[Ggmac]

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