Can you over polish the bore of a barrel.

[borderghost]

Rub a piece of glass on a piece of glass then rub sandpaper on that glass and see which has less friction. Theres a reason cylinder bores are not mirror smooth

Rub a piece of glass on a piece of glass then rub sandpaper on that glass and see which has less friction. Theres a reason cylinder bores are not mirror smooth

Hey Dusty , great information , what happens if you use coated bullets with some thing like HBN , with a polished barrel , do you think it will it still copper foul bad, seems like this HBN is real slippery and has a very high temperature range , and a lot of guys say they have to add a bit more powder to get the velocity up to where it was with bare bullets

 

[Dusty Stevens]

Hey Dusty , great information , what happens if you use coated bullets with some thing like HBN , with a polished barrel , do you think it will it still copper foul bad, seems like this HBN is real slippery and has a very high temperature range , and a lot of guys say they have to add a bit more powder to get the velocity up to where it was with bare bullets

Not a clue. Havent seen anybody use it in many years

 

[BronzeArcher]

I always had the impression that custom barrels had very good, uniform, smooth bores that reduced fowling to some degree. Is that true?

Custom barrels are much smoother and foul much less than factory barrels, in my experience.

But I expect the custom barrel makers have learned how much polishing is "just right."

 

[dgeesaman]

I always had the impression that custom barrels had very good, uniform, smooth bores that reduced fowling to some degree. Is that true?

There is an ideal amount of roughness: more rough than a mirror, smoother than a cheap factory barrel.
David

 

[Dusty Stevens]

There is an ideal amount of roughness: more rough than a mirror, smoother than a cheap factory barrel.
David

320 grit actually

 

[PigButtons]

In the "old" days of automobile racing we used to "port and polish" the intake and exhaust ports of cylinder heads and intake manifolds. Then some of the rich racing teams started paying Engineers to help build more horsepower. Soon it was "fact" that the 'polish' part of that old technique was counter productive. When two boundary layers are moving at different speeds or directions, the greater the difference in speeds the greater the turbulence zone between the layers. The turbulence is drag and works to slow the boundary layers. If you introduce a properly rough surface between the boundary layers, small eddies (whirlpools), will form relieving some of the drag. That's fluids in a tube, but something similar happens when the boundary layers are metals at high speeds. The surface of the softer metal becomes nearly a fluid and that means that the soft surface slides on the tips of the rough surface of the harder material which reduces overall contact area therefore reducing drag.

Now low speed bearing surfaces in a lubricated environment are very different, like crankshaft bearings in an engine. It this case the two metal surfaces don't actually touch because of the oil pressure that keeps them from each other. And sorry about the cylinder wall example: They are rough for the express purpose of being rough enough to "wear"/ break-in the piston rings so that they from a pressure vessel seal so that compression gases and combustion gases don't get buy and rob power or introduce "fuel" into the crank case where it would likely explode but also wash the oil off of the cylinder walls and cause premature wear of the cylinder, rings and pistons.

 

[dcali]

Every barrel maker I have ever heard has said that there is an optimal surface finish and that if you make it too smooth, bad things happen. I believe them, and I see no reason not to.

 

[338 Mollett]

Looking at a Savage barrel with it's finish and you wonder how does this thing even shoot.

 

[searcher]

Had a barrel maker tell me that if you polish the bore of a barrel to much

The logic is that the bores are polished to remove detrimental irregularities and to take to a uniform diameter. However - the smoother the bore surface is - the higher the level of surface contact with the bullet jacket - and thus more jacket material removed and a higher level of friction. Think of using an electric sander on soft wood. The fine grit paper (like 400 grit, for example) fills and clogs more rapidly than the large grits - like 50 grit.

 

[WIB3]

Been using Flitz for years, not to polish but to remove carbon. Have never had any issues. Only on a nylon brush though. The results speak for them self.

 

[WIB3]

Ultimately, it either shoots or it doesn’t. Can’t shine a turd.

 

[NorCalMikie]

Had an old time smith tell me my Wilson barrel was crap because it wasn't lapped?? One of the better/best bug hole makers I've ever owned.

 

[mikecr]

what happens if you use coated bullets with some thing like HBN , with a polished barrel , do you think it will it still copper foul bad

Coatings won't even help with a polished bore. I did a destructive test for this once. Took a barrel that passed it's accurate barrel life, but never copper fouled. Hit the bore with short cycles of Flitz, confirmed crazy copper fouling right off the bat. Coated the bore with a dry burnishing of Tungsten Disulfide (WS2, ~slipperiest stuff on Earth), and fired WS2 coated bullets. Still, bad copper fouling.
Don't ever use Fritz, or 'Bore Bright' (have a friend who ruined an awesome barrel with that).

Use 'J-B Non-Embedding Bore Cleaning Compound'
Don't get em mixed up.
Or, you can fire lap with Tubb's FinalFinish.

 

[Hal]

Had an old time smith tell me my Wilson barrel was crap because it wasn't lapped?? One of the better/best bug hole makers I've ever owned.

Wilson barrel ARE lapped, by machine, not hand lapped.

Hal

 

[Alex Wheeler]

There is actually more of a "window" of lapping grit that works than you would think. I know what most of the major guys use and have gone both ways. You dont want to polish it with something like jb, that will kill accuracy before coppering. A sharp, concentric throat is probably the most important part of a barrel, smoothing it out will ruin top accuracy and cause other issues.

 

[rwj]

There is actually more of a "window" of lapping grit that works than you would think. I know what most of the major guys use and have gone both ways. You dont want to polish it with something like jb, that will kill accuracy before coppering. A sharp throat is probably the most important part of a barrel, smoothing it out will ruin top accuracy and cause other issues.

Does the term “sharp throat” refer to the beginning of the rifling?

 

[Alex Wheeler]

Yes

 

[BDman]

A few years back, a friend of mine insisted on cleaning with a popular bore polish compound in his very accurate and expensive new barrel. The barrel looked like a mirror but accuracy continued to drop. He sent it back to the barrel maker and the owner called him after they got it. The owner was pretty funny. He said "I'll cut you some slack on a replacement barrel. But do you want a 7mm or a 7.2mm this time." My friend swore off the compounds after that.

 

[fyrewall]

Has anybody actually measured the surface roughness of rifle bores and applied values?

https://en.wikipedia.org/wiki/Surface_roughness

Or when do bad things occur?

I quit using Flitz (pleasant green mixture, has aluminum oxide, moh 9) thinking it is more scratchy than JB (mucky brown/gray mixture, has garnet, moh 7-7.5) which I only use occasionally.

That sharp concentric throat won't last very long under normal use. The lands at 6 o'clock or so on some of my rifles show more erosion than those on the top (not concentric) and as expected accuracy has suffered.

 

[dcali]

Has anybody actually measured the surface roughness of rifle bores and applied values?

https://en.wikipedia.org/wiki/Surface_roughness

Or when do bad things occur?

I quit using Flitz (pleasant green mixture, has aluminum oxide, moh 9) thinking it is more scratchy than JB (mucky brown/gray mixture, has garnet, moh 7-7.5) which I only use occasionally.
...

I don't know the answer to your question, but I can tell you that you could clean all day long for rest of your life and you will die before you remove any metal with JB. Use it freely.