Polish Chamber In New Barrel
- Thread starter Edd
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J E Custom
Well-Known Member
A very good question that is often ask Edd !
The reamed finish Is going away the best for many reasons.
First = The chamber dimensions are the truest as cut. Polishing will/can alter these dimension from the reamer. ( I have had to set back chambers that were polished because of ejection problems).
Next = The polished chamber will not grip the cartridge as well and can cause excessive bolt thrust/loading. (This can sometimes cause pressure signs early that Indicate excessive pressure that Is non existent by allowing the case head to be forced against the bolt face harder than normal).
In My opinion, A chamber that needs polishing, was ether a dull reamer or a poorly cut one by the smith. (Wrong spindle speed, dull reamer, feeding the reamer to fast, Not cleaning the reamer often enough, ETC.
If your chamber does not leave any marks on the fired brass and extracts well the reamer finish is fine.
J E CUSTOM
CatShooter
Well-Known Member
I polish all chambers with oiled #2000 Silicone Wet-n-dry.
1 - "First = The chamber dimensions are the truest as cut. Polishing will/can alter these dimension from the reamer. ( I have had to set back chambers that were polished because of ejection problems)."
I fine polish will not change the chamber dimensions, and even if it did - no two reamers are the same, so there is no set of dimensions to worry about - the amount removed by polishing is on the order of <0.0001"
2 - "Next = The polished chamber will not grip the cartridge as well and can cause excessive bolt thrust/loading. (This can sometimes cause pressure signs early that Indicate excessive pressure that Is non existent by allowing the case head to be forced against the bolt face harder than normal)."
The Blish Effect (that causes brass to stick to steel under pressure) operates on the molecular level, NOT the macro level - the case will stick to the chamber, no matter what the polish level is - plus, I do NOT want my case to stick to the chamber.
If the case sticks to the chamber on the first firing, it leaves the head unsupported, so the case stretches in front of the web... it is what causes the case to stretch. I oil the case on the first firing, so it slips back against the bolt, and does not stretch.
The case head will always wind up against the bolt face, either by stretching, or by neck sizing for following shots.
The bolt is designed to hold the pressure of case thrust (there is no such thing as bolt thrust, bolts are passive devices - it is the case that thrusts).
The idea that a ring of brass less than 0.4" in diameter, and less than 1mm thick, can somehow protect an ordnance steel bolt with lugs 1/2" wide, 1/2" thick, and 1/2" deep, and 200+ times as hard, is pure silliness.
If you neck size, the brass case head is held against the bolt face for every shot. I have one Rem 700 bought in 1975, that is on it's 6th barrel, and all of the 14,000+ 0.473" cases were neck sized - that is 14,000+ poundings with 55,000 psi cases, and the bolt lugs look new.
J E Custom
Well-Known Member
I will not be drawn into a P!$$!ng match over this but It is simple. Do It the way you want and keep believing that polishing makes the chamber
better.
I look at this like, If a chamber needs to be polished The smith didn't do his job. Also when you polish, you remove material. It Doesn't matter how much.
Sizing of ant kind doesn't keep the brass from loading the bolt any more or less. Pressure and chamber finish does. Just like lapped barrels, the finish can effect the performance and the fouling characteristics. Engine builders know that a honed finish in the cylinder is the best and that the last thing they will do is polish a cylinder because it also can change the dimensions and the straightness of the surface of the cylinder.
The comment about There being no such thing as bolt thrust is almost comical. If it does not exist, why do people have bolt lug set back that can/does increase headspace over time ? I have seen people that thought if they lubed the cases before they shot them, it would make extraction easier And all it did was wreck there action with "Excessive
bolt loading and in many instances, trash there brass. Lubing the cases is just like polishing the chamber, it increases the bolt loading.
So, polishing a chamber serves no purpose except to make a rough chamber look better. All other effects of polishing are negative In my opinion.
Again, do it like you want and live with the effects.
J E CUSTOM
Thanks for the engine cylinder analogy. I have many years of experience with them. I used the wrong term, when I said polish, in my original question. The actual finish I was asking about was that similar to a cylinder. A process where you would lightly buff a chamber with 320-400 grit emery.
J E Custom
Well-Known Member
No problem Edd. The only thing I would avoid is Buffing Because Of the risk Of changing the function Of the finish. I guess you could lightly buff with emery paper as long as you were careful and got the finish uniform/consistent throughout the chamber.
A good, sharp reamer used correctly leaves a perfect finish/surface much like a cylinder hone So I recommend leaving it alone to avoid any degradation of the chamber. Just Me.
I can appreciate the desire to make things look better (I am afflicted with this Ailment) But in this case polishing is not necessary, and risky. We tend to push the limits for long range and with higher pressures
and if things are not optimum , we can get into trouble quick.
J E CUSTOM
bigngreen
Well-Known Member
You can change surface finish without changing dimensions, many, many top smiths just make a pass with 320, many just go as reamed, I don't like that course though there is a benefit in real wet weather and I don't like as reamed because the finish look is never even so I go in between but stay to the fine side.
J E Custom
Well-Known Member
The trick is just like you said "Make a pass with 320) One pass would not change the dimensions but many people just keep polishing and polishing and that where the problem starts. While chambering I try different spindle speeds to find out what the reamer likes best and use that speed when finishing the chamber to get the proper finish.
I wish I was better at posting pictures on this site so I could show what they look like when they are right in my mind. I will try again to post some chamber pictures for reference.
Some reamers just don't leave a good finish, so I don't use them. your suggestion several years ago about JGS reamers was a good one and now I only buy JGS or Manson.
J E CUSTOM
specweldtom
Well-Known Member
specweldtom
Well-Known Member
Polish or don't polish, whatever suits you, but it suits me to NEVER fire a cartridge in an oiled chamber.
Good hunting, Tom
Good hunting, Tom
