Polishing or Not - Chambers?

[Larryjk]

It has been put forth that brightly polished chambers are the way to go; less pressure signs, better accuracy, etc. If you are a professional gunsmith, are the chambers supposed to be highly polished? If so, why?, and if not, why?
(the reason for this thread is due to a disagreement listed in the 7mm-08 Imp. thread in "Reloading".

[Adam Helmer]

Larry,

I am an armorer and hobby gunsmith. Yes, chambers should be smooth because a rough chamber makes for hard extraction; especially with near max loads. Should it be highly polished? I am sure that can be overdone to not much good purpose. More important, in my view, is to have a DRY chamber so the fired case can grasp the chamber walls and reduce thrust on the bolt face.

Adam

[happyscrounger]

i think polishing chambers started from the socalled perfectionist. in the event you end up with an oval chamber your only hope is that you can sleep at night. because you will most likely sell it to some kid with juuuust enough money. in my view the bad will out weigh the good.

[Larryjk]

I have been distracted by a thing called Income Tax. I like to sleep nights and would set the barrel back and try again if I got a "goose egg" chamber by accident. Passing such on to a non-suspecting innocent doesn't say much for a fellows integrity. Incidently some rifles used to have chambers out of round at the rear to facilitate feeding. (I won't mention Savage 99s or Winchester 88s ). A chamber polished in the lathe shouldn't end up as a "goose egg" shape. The chamber can't be turning to create a "goose egg".

A chamber cut utilizing the correct procedures should be very bright without polishing. Clean the chamber and reamer every 1/8 inch or so as to not carry a chip that will scratch the hole. It works for me.

After taxes, I am going to contact a couple of guys who have instructed at gunsmithing schools about this polishing thing.

[Ridge Runner]

Larry,
IIRC Ray Romain swears by a mirror finish on the chamber, his 6.5 Gibbs will outrun a 264 wm, thats why I posted the info that I did.
RR

[Larryjk]

Ridge Runner, There are Cadillacs and Buicks and Chevrolets. Different tastes for different drivers. I won't list the names of people who I have talked to unless I specifically get their permission. I know that the man who makes the reamers I use does not advocate polishing unless it is needed to remove a scratch. His reamers leave a very shiny chamber. Your friend does not need to highly pollish the 6.5 Gibbs chamber to get very high velocity. I shoot a 6.5-06 that is very near to the .264. The only problem to the wildcats is that we don't know what our pressures are running.

[Rapier]

There is another totally different reason to polish a chamber. Polished steel is more difficult to rust than rough steel. The higher the polish, the more resistance to rust steel has. Something to think about next time you drag your cold rifle into a warm truck or warm house. AC in the summer works just like cold in the winter. Polish the chamber and swab the bore / chamber with a lightly oiled patch it will save you a lot of grief.
Best,
Ed

[shooterjon]

Here are some tests run by varmint Al.You may find interesting and informative- http://www.varmintal.com/afric.htm

[Rapier]

I build rifles.

The information in the article is interesting but very unscientific. The information also does not correspond to brass in a firearm's chamber unless you are talking about simple insertion and extraction without firing. Any roughness in a chamber will be found by a fired case and the ability to find that rough area is only enhanced by the increase in pressure. If you increase the viscosity of the lubricant, i.e., use case lube, it does prevent the case from gripping the walls and will allow the case to fully fire form and is a process used for years by wildcatters.

Perhaps had the fellow used a press, hydrolic jack and a gage to exert X pressure on his metals his experiment might have come closer to reality. But, the base of a cartridge is not as pliable as the walls and 50-65K pressure would be, as noted, difficult to duplicate in this experiment.

Get just the slightest amount of rust in a chamber and you will learn quickly about polished or non polished chambers.
Best,
Ed

[Larryjk]

Don't get too many variables into this discussion. It was originally about "highly" polished chambers vs those made with a reamer in good shop procedures. I had proposed that a "reamer run" chamber was the most practical because the case expands in all directions under the pressure of firing (between 55k and 65k lbs./sq. in.) and is held in place by the friction between the chamber walls and the brass case. If there is no friction (as in a highly polished chamber) all of the pressure results in more bolt thrust.
If you look into a good "reamer run" chamber before the barrel is blued you will see how nice and shiny the chamber is. But if your procedure left scratches in the chamber, you will need to polish out the "rings", or set the barrel back a thread or two and recut the chamber using better cleeaning techniques. Yes, all chambers can rust if not attended to, and in my experience some calibers more than others. But that may be due to some calibers being used under more adverse conditions rather than a factor solely of the caliber.

[PJgunner]

Rough chambers? Check out a Ruger Blackhawk, either new or old model in .30Carbine. My buddy has a new Model and I hve the Old Model and the chambers are so rough they look like cross sections of the Rocky mountains.
Even the lighter cast lead plinking loads are hard to eject and full power M-1 carbine factory or milsurp ammo requires removing the cylinder and using a proper sized dowel and a hammer.
Several others of that model gun that I've looked at also have those very rough chambers.
Paul B.

[Larryjk]

PJGUNNER, Very True. I have always had trouble with ejection on my Ruger .30 carbine revolver until the cylinder chambers have become "dirty". Then ejection is okay; but I haven't figured out how to have a clean chambers in the cabinet and then have them dirty when I go shooting. Actually, the chambers on that revolver aren't any apparently rougher than the chambers on the Ruger Bisleys in .44 or .45. It has to be an idiocyncrasy of the .30 carbine case. My S&Ws in .22, .38 Spec.,.357mag, .41 mag, .44 mag, .45AR and .45 Colt have very nice shiny chambers in the clean stage.
Actually, it looks like the chambers of the .30 carbine are bored, rather than reamed. This is because of the finish I can see. I have considered polishing the .30 carbine chambers, but don't want to open them up that much. I am currently trying to have a custom revolver man turn that revolver into a .32-20.

[Ridge Runner]

Larry,
a tapered case under pressure reacts like a wedge, driving it against the bolt face, this is why in those chambers if cut even a tad big like factories do, you see the flattened primers and ejector pin marks. the less taper you have the more likely the case will adhere to a rough chamber and not push as hard against the boltface.
In my Ray Romain built rifle, you see no pressure signs, none, till you lose the pocket.
maybe the guys in the know plan it that way, they build you a rifle you load it up till its insanely fast and your happy, without knowing your pressures.
RR