Can you over polish the bore of a barrel.

[borderghost]

Had a barrel maker tell me that if you polish the bore of a barrel to much .( make it nice and smooth ) that it will foul up worse then one with a rougher surface . Have a hard time to believe this statement . As with any type of tube where something flows though it , the ideal way is to have a smooth surface , water , oil , gas, all flows with less restriction then if there is scale, build up on the inside , same with any other material flows over a smooth surface better then a rough surface , would this not hold true for the bullet transition down the barrel, be less friction , restriction , therefore less copper , carbon build up. would like to hear from someone that has more knowledge on this then myself.
Thanks for looking and replying .
Lots of good feed back here , will throw one more curve in here , As Dusty Stevens said about two pieces of glass do not slide well , roughen it up and they move much easier, or put some water between them, you can hardly keep them from moving , So what is everyone's opinion if you add HBN or some other coating to your bullets with a well polished barrel , good or bad , hope the ranges soon open, then we will not be on here .

 

[Downeast]

I'm no expert but I agree with you that a smooth "pipe" will be easier to clean than a rough "pipe". Did he use oak in his barrels?

 

[BradY]

Believe the barrel maker. Or go and get some of that purple JB Bore brite, coat a patch liberally and get it shiny as you want, void any potential warranty you may have, and enjoy high strength ammonia based copper solvents.

 

[NorCalMikie]

Funny how a "seasoned" barrel shoots better than a clean one.
Clean it "real good" and you'll have to season it till it shoots better.

 

[FeMan]

At the speeds bullets are going in a barrel, I am not sure friction acts the way we normally think it does. Even in your tube analogy of fluid mechanics, smooth and a laminar flow is better most of the time. However, it you get things going fast enough the friction actually decreases with a rough wall and turbulent boundary layer. That's why golf balls aren't smooth.

Bullets against steel aren't fluid mechanics though. I have heard and subscribe to the theory that the first couples inches of the bore, where bullets speed is less can benefit from polishing but beyond that, over-polishing can add to copper fouling. I can't remember where I heard that theory but as an engineer, it made sense to me.

 

[rardoin]

Had a barrel maker tell me that if you polish the bore of a barrel to much .( make it nice and smooth ) that it will foul up worse then one with a rougher surface . Have a hard time to believe this statement . As with any type of tube where something flows though it , the ideal way is to have a smooth surface , water , oil , gas, all flows with less restriction then if there is scale, build up on the inside , same with any other material flows over a smooth surface better then a rough surface , would this not hold true for the bullet transition down the barrel, be less friction , restriction , therefore less copper , carbon build up. would like to hear from someone that has more knowledge on this then myself.
Thanks for looking and replying .

Your assumptions on surface drag in fluid dynamics are incorrect. Regardless, their application in jacket interaction with the bore surface would not apply. It has been long established that a highly polished bore will cause more 'smear' of copper than one with a more rough surface. I'll let the mechanical engineers explain why.

 

[Ramblerman]

At the speeds bullets are going in a barrel, I am not sure friction acts the way we normally think it does. Even in your tube analogy of fluid mechanics, smooth and a laminar flow is better most of the time. However, it you get things going fast enough the friction actually decreases with a rough wall and turbulent boundary layer. That's why golf balls aren't smooth.

Bullets against steel aren't fluid mechanics though. I have heard and subscribe to the theory that the first couples inches of the bore, where bullets speed is less can benefit from polishing but beyond that, over-polishing can add to copper fouling. I can't remember where I heard that theory but as an engineer, it made sense to me.

There was some testing done on boat hulls I remember.... specifically on personal watercraft...they were were doing speed trials and the craft were marginally faster with that super smooth gel coat "broken" or scuffed with a light abrasive... Scotch brite if i remember correctly...not necessarily apples to apples...but interesting.

 

[Mark W]

The way I picture this is that surface with some texture will have less surface contact than a super smooth surface. It makes perfect sense to me that a polished smooth surface will have more friction and fouling.

 

[BoydAllen]

I run into this from time to time. With no more than their imaginings to go on, fellows will discount information that comes from experience. Believe the barrel maker. Next time someone who has a lot of experience in a field tells you something, based on a lot of experience, that is not consistent with your imaginings, realize that experience trumps imaginings every time. A friend has learned how to lap finished barrels that have issues. Back in the beginning, he had had some success with a fine grit on a .22 rimfire barrel. When he tried doing one for centerfire with jacketed bullets he was struggling until I told him what your barrel maker told you. At first he had a lot of trouble believing what I had told him, and went back and forth with coarser and smoother finishes until he finally believed what I had passed on from my reading and conversations.

 

[dgeesaman]

Forgive me for speaking in generalities but as with many engineering subjects, the optimal surface profile “depends”.

Reynolds number drives the optimal choice in fluids passing around solid objects. For a golf ball or swimming suit, Reynolds number is in a range that dimples or roughness reduce the overall drag compared to a smooth one. At different speeds, sizes, and fluids, it will not be true. Race cars and airplanes are mostly very smooth surfaces.

Surfaces dragging directly against each other is a wildly complicated subject. In almost every case, the reality is you try stuff first and try to explain it later. Rifle barrels can be left in this category. It would seem that an over polished bore may behave like gauge block surfaces, where they are so smooth there is no air left in between and they literally stick together.

 

[Dusty Stevens]

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

 

[borderghost]

Well this has been a very informative subject , thanks for all the reply's on the subject , nice to hear from the people that has the knowledge, once again thanks

 

[wkdickinson]

There was some testing done on boat hulls I remember.... specifically on personal watercraft...they were were doing speed trials and the craft were marginally faster with that super smooth gel coat "broken" or scuffed with a light abrasive... Scotch brite if i remember correctly...not necessarily apples to apples...but interesting.

It seems to me that about 30 or 40 years ago, America's Cup hull designers figured out that a hull that had a uniformly "rough" (relatively speaking) surface, caused less drag in the water, than one polished smooth.

 

[Ranger188]

As others have mentioned, but don't know if it applies to rifle barrels
is the race boats on the water have ruffed up hulls. They will "sand" the
bottoms length wise to break up the flow of water, less contact.

 

[dgeesaman]

As others have mentioned, but don't know if it applies to rifle barrels
is the race boats on the water have ruffed up hulls. They will "sand" the
bottoms length wise to break up the flow of water, less contact.

It might help optimize the performance of a squirt gun barrel, but the reasoning has nothing to do with bullets passing through a dry barrel.

 

[Ackman]

The barrelmaker is correct. I've experienced it with one of my own barrels. A like new/old Apex barrel originally .222, rechambered to .221 in '90. For many years and many-many thousands of rounds, even after shooting a couple 100 rounds the thing fouled very little and never coppered, not even a trace of blue. It was like this for a long long time. Then a few years ago I started seeing blue when cleaning it. And run ning a patch through this thing the bore has become the smoothest I've ever felt. Even on a very smooth lapped new custom bore, the bullet rides on microscopic ridges. When it finally becomes super smooth, there's more bore to bullet surface. This barrel still shoots fine, but it fouls and coppers more now and takes longer to clean than it used to.

 

[Downeast]

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

 

[AckleymanII]

I was given a barrel once from a top barrel maker that was "Over polished". The barrel was chambered in 223.

IN 40 shots, the barrel's bore looked gold plated...solid copper. The barrel was very accurate, however. Lots of work to get all that copper out.

 

[NorCalMikie]

IN 40 shots, the barrel's bore looked gold plated...solid copper. The barrel was very accurate, however. Lots of work to get all that copper out.

That's what you get for looking with a bore scope.
The old saying "don't fix it if it ain't broke".

 

[AckleymanII]

No bore scope was used on the over polished barrel, just looked into the muzzle. Accuracy of course started to get very bad, and actually saw pressure increase from so much copper in the barrel.

I got the barrel free because it was an experimental 9 Groove with shallow lands, barrel maker was playing with a new rifling button design.